US20090027124A1 - Level-Shifting Buffer - Google Patents
Level-Shifting Buffer Download PDFInfo
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- US20090027124A1 US20090027124A1 US12/241,935 US24193508A US2009027124A1 US 20090027124 A1 US20090027124 A1 US 20090027124A1 US 24193508 A US24193508 A US 24193508A US 2009027124 A1 US2009027124 A1 US 2009027124A1
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/45475—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using IC blocks as the active amplifying circuit
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/45179—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using MOSFET transistors as the active amplifying circuit
- H03F3/45183—Long tailed pairs
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45101—Control of the DC level being present
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45134—Indexing scheme relating to differential amplifiers the whole differential amplifier together with other coupled stages being fully differential realised
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45138—Two or more differential amplifiers in IC-block form are combined, e.g. measuring amplifiers
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45511—Indexing scheme relating to differential amplifiers the feedback circuit [FBC] comprising one or more transistor stages, e.g. cascaded stages of the dif amp, and being coupled between the loading circuit [LC] and the input circuit [IC]
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45641—Indexing scheme relating to differential amplifiers the LC being controlled, e.g. by a signal derived from a non specified place in the dif amp circuit
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45652—Indexing scheme relating to differential amplifiers the LC comprising one or more further dif amp stages, either identical to the dif amp or not, in cascade
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45668—Indexing scheme relating to differential amplifiers the LC comprising a level shifter circuit, which does not comprise diodes
Definitions
- the present disclosure generally relates to the field of input/output circuitry in integrated circuits.
- the present disclosure is directed to a level-shifting buffer for providing signal amplitude and/or common mode adjustment in an integrated circuit receiver.
- a typical differential analog receiver in an integrated circuit contains a first stage that is powered by a first power supply, such as a VDDIO supply.
- the first stage is followed by a second stage that is powered by a core power supply, such as a VDD supply.
- VDDIO may be, for example, be 3.3 volts, 2.5 volts, 1.8 volts, or 1.5 volts.
- the core power supply voltage is decreasing.
- the VDD supply may be about 1.0 volts.
- a nominal VDD supply of about 1.0 volts may be as low as 0.7 volts.
- the output common mode of the first stage of the differential analog receiver may be higher than the input common mode of the second stage because, in one example, the output common mode of the first stage may be higher than the VDD supply voltage.
- the output common mode of the first stage falls within the input common mode range of the second stage, but in other cases it may fall outside the range and, thus, the second stage will not be able to amplify the signal from the first stage.
- the differential output of the first stage may have a very large amplitude variation as a result of both the wide VDDIO range and wide input dynamic range. This can cause a reliability problem because the second stage uses native oxide devices and the maximum voltage that the gate-oxide of the second stage may withstand may be much less than the signal levels of the first stage. In some cases, the signal levels of the first stage drive a voltage of more than the maximum voltage that is allowed across the gate-oxide of the second stage, which may cause gate-oxide damage that may cause reliability problems.
- a PFET level shifting differential amplifier includes a first power supply; a second power supply; a pair of differential inputs; a first PFET having a first gate in electrical communication with a first one of the pair of differential inputs, a first terminal in electrical communication with the first power supply, and a second terminal; a second PFET in parallel with the first PFET, the second PFET having a second gate in electrical communication with a second one of the pair of differential inputs, a third terminal in electrical communication with the first power supply, and a fourth terminal; a first adjustable impedance element electrically connected between the second terminal and the second power supply; a second adjustable impedance element in parallel with the first adjustable impedance element, the second adjustable impedance element being electrically connected between the fourth terminal and the second power supply; a first output node electrically connected between the second terminal and the first adjustable impedance element; a second output node electrically connected between the fourth terminal and the second adjustable impedance element; and a third adjustable
- a PFET level shifting differential amplifier in another embodiment, includes a first power supply; a second power supply; a pair of differential inputs; a first PFET having a first gate in electrical communication with a first one of the pair of differential inputs, a first terminal in electrical communication with the first power supply, and a second terminal; a second PFET in parallel with the first PFET, the second PFET having a second gate in electrical communication with a second one of the pair of differential inputs, a third terminal in electrical communication with the first power supply, and a fourth terminal; a first adjustable impedance element electrically connected between the second terminal and the second power supply; a second adjustable impedance element in parallel with the first adjustable impedance element, the second adjustable impedance element being electrically connected between the fourth terminal and the second power supply, wherein the first and second adjustable impedance elements each include a first pass gate; a first output node electrically connected between the second terminal and the first adjustable impedance element; a second output node electrically
- FIG. 2 illustrates a schematic diagram of an example of a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver
- FIG. 3 illustrates a schematic diagram of another example of a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver
- FIG. 4 illustrates a schematic diagram of yet another example of a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver
- FIG. 5 illustrates a schematic diagram of another example of a receiver system that includes yet another example of a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver.
- Embodiments of the present disclosure include an analog level-shifting buffer for providing signal amplitude and common mode adjustment in an integrated circuit receiver.
- a receiver system may include a first amplification stage that is powered, for example, via an I/O power supply (e.g., VDDIO) and a second amplification stage that is powered, for example, via a core logic power supply (e.g., VDD).
- I/O power supply e.g., VDDIO
- VDD core logic power supply
- Arranged between the first and second amplification stages may be the analog level-shifting buffer.
- a level-shifting buffer may ensure, via a set of variable impedance elements, that the output common mode of the analog level-shifting buffer is within the range of the input common mode of the second amplification stage and/or that the output signal amplitude of the analog level-shifting buffer is not sufficiently large to cause gate-oxide damage within the second amplification stage.
- the resistance of the variable impedance elements may vary as a function of a power supply voltage, such as the VDDIO voltage, and the input signal swing and, thus, the output common mode and signal amplitude may be adjusted as a function of the power supply voltage and/or the input signal swing.
- FIG. 1 illustrates a high level block diagram of a receiver system 100 , which is an example of a receiver system that includes a level shifter circuit for providing signal amplitude and/or common mode adjustment in an integrated circuit receiver.
- Receiver system 100 may include a first amplification stage 110 that is fed by differential input signals 112 and 114 and provides differential output signals 116 and 118 .
- First amplification stage 110 may be the input/output (I/O) interface of an integrated circuit (IC) for receiving a differential signal pair from outside of the IC chip.
- First amplification stage 110 may be electrically connected between a first power rail 140 and a second power rail 142 .
- first power rail 140 may be a dedicated power supply, such as a dedicated power supply for input/output circuits (e.g., VDDIO).
- first power rail 140 may have a voltage range of about 1.5 volts to about 3.3 volts.
- second power rail 142 may be a ground rail (e.g., about 0 volts) of an integrated circuit.
- receiver system 100 may include a second amplification stage 120 that is fed by differential input signals 122 and 124 and provides differential output signals 126 and 128 .
- Second amplification stage 120 may be the stage of the IC receiver system that passes the I/O signal to the core logic of the IC chip.
- Second amplification stage 120 may be electrically connected between a third power rail 144 and second power rail 142 .
- third power rail 144 may be a dedicated power supply (e.g., VDD or VCC) for the core logic of an integrated circuit that may have a voltage range of, for example, but not limited to, about 0.9 volts to about 1.1 volts.
- receiver system 100 may include a level shifting stage 130 that is fed by differential input signals 132 and 134 and provides differential output signals 136 and 138 .
- Level shifting stage 120 may be electrically connected between first power rail 140 and second power rail 142 .
- Level shifting stage 130 may be a buffer stage that is provided between first amplification stage 110 and second amplification stage 120 of an integrated circuit receiver for receiving an input from first amplification stage 110 that has a certain signal amplitude and common mode and providing an output of another certain signal amplitude and common mode that is compatible with second amplification stage 120 .
- the common mode of differential output signals 136 and 138 of level shifting stage 130 may be within the range of the input common mode of second amplification stage 120 and the signal amplitude is not sufficiently large to cause gate-oxide damage within second amplification stage 120 .
- the shift in amplitude and common mode within level shifting stage 130 may be a function of the voltage level of first power rail 140 .
- level shifting stage 130 may minimize the variation of the output common mode voltage such that it is maintained always within the input common mode range of second amplification stage 120 .
- level shifting stage 130 may amplify or attenuate the signal amplitude of first amplification stage 110 . In such and example, when the output signal amplitude of first amplification stage 110 is large, no amplification or attenuation may be provided. By contrast, when the output signal amplitude of first amplification stage 110 is small, amplification may be provided.
- first power rail 140 may be about 2.5 volts
- second power rail 142 may be about 0 volts (ground)
- third power rail 144 may be about 1 volts
- the amplitude of output signals 116 and 118 of first amplification stage 110 may be about 1 volts
- the output common mode of first amplification stage 110 may be about 1.25 volts
- the amplitude of output signals 136 and 138 of level shifting stage 130 may be about 0.5 volts
- the output common mode of level shifting stage 130 may be about 0.5 volts, in order to be compatible with the input signal amplitude and the input common mode of second amplification stage 120 .
- FIG. 2 illustrates a schematic diagram of one embodiment of a level shifter circuit 200 .
- Level shifter circuit 200 may be an level-shifting buffer that is connected between first power rail 140 and second power rail 142 .
- level shifter circuit 200 may include a pair of p-type field-effect transistors (PFETS) 212 and 214 whose sources are connected at a node 216 .
- PFETS p-type field-effect transistors
- Constant current source element 218 may regulate (i.e., limit) the circuit of level shifter circuit 200 to a certain constant current flow, regardless of variations in first power rail 140 and second power rail 142 .
- constant current source element 218 may be a FET device that is controlled to provide a constant current.
- the gate of transistor 212 may be in electrical communication with an input signal node 220 , which may be the first of two differential input signals, and the gate of transistor 214 may be in electrical communication with an input signal node 222 , which may be the second of two differential input signals of level shifter circuit 200 .
- a first impedance element 224 may be connected between a first terminal (e.g., a drain) of transistor 212 and second power rail 142 .
- a second impedance element 226 may be connected between a first terminal (e.g., a drain) of transistor 214 and second power rail 142 .
- An output signal node 230 is electrically positioned between transistor 212 and impedance element 224 .
- An output signal node 232 is electrically positioned between transistor 214 and impedance element 226 .
- Output signal nodes 230 , 232 may be differential output nodes.
- a third impedance element 228 may be connected between output signal node 230 and output signal node 232 .
- First impedance element 224 , second impedance element 226 , and third impedance element 228 may be variable resistance elements.
- the resistance of first impedance element 224 , second impedance element 226 , and third impedance element 228 may be inversely proportional to the voltage value at first power rail 140 , i.e., as the voltage value at first power rail 140 increases the resistance of first impedance element 224 , second impedance element 226 , and third impedance element 228 decreases.
- Example impedance elements may include, but are not limited to, a n-type field-effect transistor (NFET) device, a PFET device, a diode-connected FET device, and any combinations thereof. More details of example impedance elements are found with reference to FIGS. 3 , 4 , and 5 .
- differential input signals of a certain signal amplitude and input common mode are provided at input signal nodes 220 and 222 .
- the signal amplitude at output signal nodes 230 and 232 may be a fraction or multiple of the amplitude of input signal nodes 220 and 222 depending on the resistance value of third impedance element 228 , which varies as a function of, for example, first power rail 140 .
- the impedance of third impedance element 228 is smaller and, thus, level shifter circuit 200 provides less amplification to a large input swing. As a result, the output swing of level shifter circuit 200 tends not to depend on the input swing.
- the resistance of third impedance element 228 decreases and, thus, the amplitude of output signal nodes 230 and 232 tends to decrease because the voltage drop across third impedance element 228 decreases and, thus, the overall variation of the output swing with respect to variations in first power rail 140 is small.
- the output common mode at output signal nodes 230 and 232 depends on the resistance value of first impedance element 224 and second impedance element 226 , which varies as a function of, for example, first power rail 140 .
- first impedance element 224 and second impedance element 226 decreases and, thus, the signals at output signal nodes 230 and 232 are pulled closer to the voltage at, for example, second power rail 142 (e.g., ground) because the voltage drop across first impedance element 224 and second impedance element 226 decreases.
- the resistance of first impedance element 224 and second impedance element 226 determines the output common node at output signal nodes 230 and 232 .
- the signal amplitude and input common mode at input signal nodes 220 and 222 may be shifted as a function of, for example, the value of first power rail 140 , which causes a change (e.g., inversely proportional change) in the resistance of first impedance element 224 , second impedance element 226 , and third impedance element 228 .
- the signal amplitude and/or common mode at output signal nodes 230 and 232 may be adjusted as compared with the signal amplitude and common mode at input signal nodes 220 and 222 .
- level shifter circuit 200 may provide signal amplitude and/or common mode translation between, for example, first amplification stage 110 and second amplification stage 120 of FIG. 1 , in order to ensure that the common mode of output signal nodes 230 and 232 is within the range of the input common mode of second amplification stage 120 and that the signal amplitude is not sufficiently large to cause gate-oxide damage within second amplification stage 120 .
- FIG. 3 illustrates a schematic diagram of another embodiment of a level shifter circuit 300 .
- FIG. 3 shows an example embodiment of the impedance elements within a level shifter circuit, such as level shifter circuit 300 .
- level shifter circuit 300 may include a first impedance element 324 , a second impedance element 326 , and a third impedance element 328 that are each formed by a pair of parallel-connected transistors.
- each is formed by an NFET device and a PFET device that are electrically connected in parallel as shown in FIG. 3 .
- the gate of each NFET device may be electrically connected to first power rail 140 and the gate of each PFET device may be electrically connected to second power rail 142 (e.g., ground).
- the resistance of each parallel-connected transistor may vary inversely proportional to the voltage value at first power rail 140 .
- the impedance of the PFETs of first impedance element 324 and second impedance element 326 may be determined by the voltage of nodes 330 and 332 minus the voltage of second power rail 142 . In such an example, when the output common mode is high that means the voltage of nodes 330 and 332 is high, which leads to smaller resistance of the PFETs of first impedance element 324 and second impedance element 326 and, thus, the voltage of nodes 330 and 332 is dragged down (i.e., toward the voltage of second power rail 142 ).
- the PFETs of first impedance element 324 and second impedance element 326 try to prevent the output common mode from going high.
- the impedance of the PFET of third impedance element 328 may be determined by the voltage of nodes 330 and 332 minus the voltage of second power rail 142 .
- the PFET of third impedance element 328 may prevent the output swing from going high.
- first impedance element 324 , second impedance element 326 , and third impedance element 328 may be variable resistance impedance elements for adjusting the signal amplitude and/or common mode at output signal nodes 330 and 332 as compared with the signal amplitude and common mode at input signal nodes 320 and 322 .
- the NFET of third impedance element 328 may have a characteristic that is similar to the PFET of third impedance element 328 . More specifically, the impedance of the NFET of third impedance element 328 may be determined by the difference between first power rail 140 and the minimum voltage of nodes 330 and 332 . Therefore, when the output swing is larger, the minimum voltage of nodes 330 and 332 is smaller, and the impedance of the NFET of third impedance element 328 is small. This may prevent the output swing from going high. In such an example, level shifter circuit 300 may provide signal amplitude and/or common mode translation between, for example, first amplification stage 110 and second amplification stage 120 of FIG.
- FIG. 4 illustrates a schematic diagram of yet another embodiment of a level shifter circuit 400 .
- FIG. 4 shows an example embodiment of the impedance elements within a level shifter circuit, such as level shifter circuit 400 .
- level shifter circuit 400 may include a first impedance element 424 , a second impedance element 426 , and a third impedance element 428 .
- first impedance element 424 and second impedance element 426 may each be formed by a pair of parallel-connected transistors as shown in FIG. 4 and may be substantially identical in form and function to first impedance element 324 and second impedance element 326 of level shifter circuit 300 , as described in FIG. 3 .
- the third impedance element such as third impedance element 428
- the third impedance element 428 may be formed of a pair of diode-connected transistors, such as a pair of diode-connected NFET devices.
- the diode-connected transistors of third impedance element 428 are always turned on, but the higher the voltage swing at output signal nodes 430 and 432 , the more strongly the diode-connected transistors are turned on and, thus, the more the resistance of third impedance element 428 decreases, which minimizes the variation of the output swing with respect to input swing.
- first impedance element 424 , second impedance element 426 , and the diode-connected transistor arrangement of third impedance element 428 each may be a variable resistance impedance element for adjusting the signal amplitude and/or common mode at output signal nodes 430 and 432 as compared with the signal amplitude and common mode at input signal nodes 420 and 422 .
- level shifter circuit 400 may provide signal amplitude and/or common mode translation between first amplification stage 110 and second amplification stage 120 of FIG.
- FIG. 5 illustrates a schematic diagram of a receiver system 500 , which is another example of a receiver system that includes a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver.
- Receiver system 500 may include a level shifter circuit 504 , which may be another example embodiment of level shifting stage 130 of FIG. 1 , that may be arranged between first power rail 140 and second power rail 142 (e.g., ground).
- receiver system 500 may include a second amplification stage 506 , which may be an example embodiment of second amplification stage 120 of FIG. 1 , that may be arranged between third power rail 144 and second power rail 142 (e.g., ground).
- the signal amplitude and common mode at output signal nodes 530 and 532 are adjusted as compared with the signal amplitude and common mode at input signal nodes 520 and 522 .
- Output signal nodes 530 and 532 drive the gates of a pair of transistors 540 and 544 , respectively, of second amplification stage 506 .
- a load 548 may be connected between signal output nodes 542 and 546 , respectively, and a third power rail 144 .
- An opposite side of transistors 540 and 544 is connected to a voltage node 550 .
- a transistor 552 which may be a constant current source element, may be connected between voltage node 550 and second power rail 142 (e.g., ground).
- the common mode may be optimized with regard to third power rail 144 and the current through optional transistor 552 .
- feedback circuit 508 optionally includes a mechanism for providing a common mode adjustment that is a function of third power rail 144 .
- feedback circuit 508 may include a diode-connected transistor 570 between third power rail 144 and second power rail 142 (e.g., ground), as shown in FIG. 5 .
- circuit 500 may include a resistor 522 .
- a voltage node 574 at diode-connected transistor 570 may be connected to the gate of transistor 552 of second amplification stage 506 .
- diode-connected transistor 570 may provide dependence on third power rail 144 to the common mode of output signal nodes 530 and 532 of level shifter circuit 504 .
- third power rail 144 increases the current through transistor 552 may increase (and voltage node 550 may decrease), which may result in larger common mode of output signal nodes 530 and 532 of level shifter circuit 504 and transistors 540 and 544 have sufficient overdrive voltage.
- receiver system 500 may provide a common mode that tracks to third power rail 144 and counter tracks to first power rail 140 . In such an example, it may be ensured that the voltage at output signal nodes 530 and 532 of level shifter circuit 504 may not be sufficiently large to damage transistors 540 and 544 of second amplification stage 506 .
Abstract
Description
- This application is a continuation of U.S. patent application Ser. No. 11/623,185, filed Jan. 15, 2007, entitled “Level-Shifting Buffer,” which is incorporated herein by reference in its entirety.
- The present disclosure generally relates to the field of input/output circuitry in integrated circuits. In particular, the present disclosure is directed to a level-shifting buffer for providing signal amplitude and/or common mode adjustment in an integrated circuit receiver.
- A typical differential analog receiver in an integrated circuit contains a first stage that is powered by a first power supply, such as a VDDIO supply. The first stage is followed by a second stage that is powered by a core power supply, such as a VDD supply. VDDIO may be, for example, be 3.3 volts, 2.5 volts, 1.8 volts, or 1.5 volts. However, as integrated circuit technology scales the core power supply voltage is decreasing. For example, the VDD supply may be about 1.0 volts. Problems arise as technology scales and the voltage difference between VDDIO and VDD increases.
- When power supply variations and chip IR drop in an integrated circuit are considered, a nominal VDD supply of about 1.0 volts may be as low as 0.7 volts. The output common mode of the first stage of the differential analog receiver may be higher than the input common mode of the second stage because, in one example, the output common mode of the first stage may be higher than the VDD supply voltage. In some cases, the output common mode of the first stage falls within the input common mode range of the second stage, but in other cases it may fall outside the range and, thus, the second stage will not be able to amplify the signal from the first stage.
- Additionally, the differential output of the first stage may have a very large amplitude variation as a result of both the wide VDDIO range and wide input dynamic range. This can cause a reliability problem because the second stage uses native oxide devices and the maximum voltage that the gate-oxide of the second stage may withstand may be much less than the signal levels of the first stage. In some cases, the signal levels of the first stage drive a voltage of more than the maximum voltage that is allowed across the gate-oxide of the second stage, which may cause gate-oxide damage that may cause reliability problems.
- A need exists for a level-shifting buffer for providing signal amplitude and/or common mode adjustment in an integrated circuit receiver.
- In one embodiment, a PFET level shifting differential amplifier is provided. The amplifier includes a first power supply; a second power supply; a pair of differential inputs; a first PFET having a first gate in electrical communication with a first one of the pair of differential inputs, a first terminal in electrical communication with the first power supply, and a second terminal; a second PFET in parallel with the first PFET, the second PFET having a second gate in electrical communication with a second one of the pair of differential inputs, a third terminal in electrical communication with the first power supply, and a fourth terminal; a first adjustable impedance element electrically connected between the second terminal and the second power supply; a second adjustable impedance element in parallel with the first adjustable impedance element, the second adjustable impedance element being electrically connected between the fourth terminal and the second power supply; a first output node electrically connected between the second terminal and the first adjustable impedance element; a second output node electrically connected between the fourth terminal and the second adjustable impedance element; and a third adjustable impedance element electrically connected between the first and second output nodes, the third adjustable impedance element includes a first diode connected FET.
- In another embodiment, a PFET level shifting differential amplifier is provided. The amplifier includes a first power supply; a second power supply; a pair of differential inputs; a first PFET having a first gate in electrical communication with a first one of the pair of differential inputs, a first terminal in electrical communication with the first power supply, and a second terminal; a second PFET in parallel with the first PFET, the second PFET having a second gate in electrical communication with a second one of the pair of differential inputs, a third terminal in electrical communication with the first power supply, and a fourth terminal; a first adjustable impedance element electrically connected between the second terminal and the second power supply; a second adjustable impedance element in parallel with the first adjustable impedance element, the second adjustable impedance element being electrically connected between the fourth terminal and the second power supply, wherein the first and second adjustable impedance elements each include a first pass gate; a first output node electrically connected between the second terminal and the first adjustable impedance element; a second output node electrically connected between the fourth terminal and the second adjustable impedance element; and a third adjustable impedance element electrically connected between the first and second output nodes, the third adjustable impedance element includes a first diode connected FET, wherein a differential swing between the first and second output nodes is a function of a differential swing between the pair of differential inputs and an output common mode at the first and second output nodes is a function of the first power supply.
- For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:
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FIG. 1 illustrates a high level block diagram of an example of a receiver system that includes a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver; -
FIG. 2 illustrates a schematic diagram of an example of a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver; -
FIG. 3 illustrates a schematic diagram of another example of a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver; -
FIG. 4 illustrates a schematic diagram of yet another example of a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver; and -
FIG. 5 illustrates a schematic diagram of another example of a receiver system that includes yet another example of a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver. - Embodiments of the present disclosure include an analog level-shifting buffer for providing signal amplitude and common mode adjustment in an integrated circuit receiver. In one example, a receiver system may include a first amplification stage that is powered, for example, via an I/O power supply (e.g., VDDIO) and a second amplification stage that is powered, for example, via a core logic power supply (e.g., VDD). Arranged between the first and second amplification stages may be the analog level-shifting buffer. In one exemplary aspect, a level-shifting buffer may ensure, via a set of variable impedance elements, that the output common mode of the analog level-shifting buffer is within the range of the input common mode of the second amplification stage and/or that the output signal amplitude of the analog level-shifting buffer is not sufficiently large to cause gate-oxide damage within the second amplification stage. The resistance of the variable impedance elements may vary as a function of a power supply voltage, such as the VDDIO voltage, and the input signal swing and, thus, the output common mode and signal amplitude may be adjusted as a function of the power supply voltage and/or the input signal swing.
-
FIG. 1 illustrates a high level block diagram of areceiver system 100, which is an example of a receiver system that includes a level shifter circuit for providing signal amplitude and/or common mode adjustment in an integrated circuit receiver.Receiver system 100 may include afirst amplification stage 110 that is fed bydifferential input signals differential output signals First amplification stage 110 may be the input/output (I/O) interface of an integrated circuit (IC) for receiving a differential signal pair from outside of the IC chip.First amplification stage 110 may be electrically connected between afirst power rail 140 and asecond power rail 142. In one example,first power rail 140 may be a dedicated power supply, such as a dedicated power supply for input/output circuits (e.g., VDDIO). In another example,first power rail 140 may have a voltage range of about 1.5 volts to about 3.3 volts. In yet another example,second power rail 142 may be a ground rail (e.g., about 0 volts) of an integrated circuit. - Additionally,
receiver system 100 may include asecond amplification stage 120 that is fed bydifferential input signals differential output signals Second amplification stage 120 may be the stage of the IC receiver system that passes the I/O signal to the core logic of the IC chip.Second amplification stage 120 may be electrically connected between athird power rail 144 andsecond power rail 142. In one example,third power rail 144 may be a dedicated power supply (e.g., VDD or VCC) for the core logic of an integrated circuit that may have a voltage range of, for example, but not limited to, about 0.9 volts to about 1.1 volts. - Additionally,
receiver system 100 may include alevel shifting stage 130 that is fed bydifferential input signals differential output signals Level shifting stage 120 may be electrically connected betweenfirst power rail 140 andsecond power rail 142.Level shifting stage 130 may be a buffer stage that is provided betweenfirst amplification stage 110 andsecond amplification stage 120 of an integrated circuit receiver for receiving an input fromfirst amplification stage 110 that has a certain signal amplitude and common mode and providing an output of another certain signal amplitude and common mode that is compatible withsecond amplification stage 120. In one example, the common mode ofdifferential output signals level shifting stage 130 may be within the range of the input common mode ofsecond amplification stage 120 and the signal amplitude is not sufficiently large to cause gate-oxide damage withinsecond amplification stage 120. - The shift in amplitude and common mode within
level shifting stage 130 may be a function of the voltage level offirst power rail 140. In particular, when the voltage level offirst power rail 140 varies,level shifting stage 130 may minimize the variation of the output common mode voltage such that it is maintained always within the input common mode range ofsecond amplification stage 120. Additionally,level shifting stage 130 may amplify or attenuate the signal amplitude offirst amplification stage 110. In such and example, when the output signal amplitude offirst amplification stage 110 is large, no amplification or attenuation may be provided. By contrast, when the output signal amplitude offirst amplification stage 110 is small, amplification may be provided. - In one example,
first power rail 140 may be about 2.5 volts,second power rail 142 may be about 0 volts (ground),third power rail 144 may be about 1 volts, the amplitude ofoutput signals first amplification stage 110 may be about 1 volts, the output common mode offirst amplification stage 110 may be about 1.25 volts, the amplitude ofoutput signals level shifting stage 130 may be about 0.5 volts, and the output common mode oflevel shifting stage 130 may be about 0.5 volts, in order to be compatible with the input signal amplitude and the input common mode ofsecond amplification stage 120. -
FIG. 2 illustrates a schematic diagram of one embodiment of alevel shifter circuit 200.Level shifter circuit 200 may be an level-shifting buffer that is connected betweenfirst power rail 140 andsecond power rail 142. In particular,level shifter circuit 200 may include a pair of p-type field-effect transistors (PFETS) 212 and 214 whose sources are connected at anode 216. Optionally connected betweennode 216 andfirst power rail 140 may be a constantcurrent source element 218, which may be an ideal constant current source. Constantcurrent source element 218 may regulate (i.e., limit) the circuit oflevel shifter circuit 200 to a certain constant current flow, regardless of variations infirst power rail 140 andsecond power rail 142. In one example, constantcurrent source element 218 may be a FET device that is controlled to provide a constant current. - The gate of
transistor 212 may be in electrical communication with aninput signal node 220, which may be the first of two differential input signals, and the gate oftransistor 214 may be in electrical communication with aninput signal node 222, which may be the second of two differential input signals oflevel shifter circuit 200. Afirst impedance element 224 may be connected between a first terminal (e.g., a drain) oftransistor 212 andsecond power rail 142. Asecond impedance element 226 may be connected between a first terminal (e.g., a drain) oftransistor 214 andsecond power rail 142. Anoutput signal node 230 is electrically positioned betweentransistor 212 andimpedance element 224. Anoutput signal node 232 is electrically positioned betweentransistor 214 andimpedance element 226.Output signal nodes third impedance element 228 may be connected betweenoutput signal node 230 andoutput signal node 232. -
First impedance element 224,second impedance element 226, andthird impedance element 228 may be variable resistance elements. In one example, the resistance offirst impedance element 224,second impedance element 226, andthird impedance element 228 may be inversely proportional to the voltage value atfirst power rail 140, i.e., as the voltage value atfirst power rail 140 increases the resistance offirst impedance element 224,second impedance element 226, andthird impedance element 228 decreases. Example impedance elements may include, but are not limited to, a n-type field-effect transistor (NFET) device, a PFET device, a diode-connected FET device, and any combinations thereof. More details of example impedance elements are found with reference toFIGS. 3 , 4, and 5. - In operation, differential input signals of a certain signal amplitude and input common mode are provided at
input signal nodes output signal nodes input signal nodes third impedance element 228, which varies as a function of, for example,first power rail 140. Also when the input swing is large, the impedance ofthird impedance element 228 is smaller and, thus,level shifter circuit 200 provides less amplification to a large input swing. As a result, the output swing oflevel shifter circuit 200 tends not to depend on the input swing. In one example, as the voltage value atfirst power rail 140 increases the resistance ofthird impedance element 228 decreases and, thus, the amplitude ofoutput signal nodes third impedance element 228 decreases and, thus, the overall variation of the output swing with respect to variations infirst power rail 140 is small. Additionally, the output common mode atoutput signal nodes first impedance element 224 andsecond impedance element 226, which varies as a function of, for example,first power rail 140. In one example, as the voltage value atfirst power rail 140 increases the resistance offirst impedance element 224 andsecond impedance element 226 decreases and, thus, the signals atoutput signal nodes first impedance element 224 andsecond impedance element 226 decreases. In one example, the resistance offirst impedance element 224 andsecond impedance element 226 determines the output common node atoutput signal nodes level shifter circuit 200, the signal amplitude and input common mode atinput signal nodes first power rail 140, which causes a change (e.g., inversely proportional change) in the resistance offirst impedance element 224,second impedance element 226, andthird impedance element 228. In such an example, the signal amplitude and/or common mode atoutput signal nodes input signal nodes level shifter circuit 200 may provide signal amplitude and/or common mode translation between, for example,first amplification stage 110 andsecond amplification stage 120 ofFIG. 1 , in order to ensure that the common mode ofoutput signal nodes second amplification stage 120 and that the signal amplitude is not sufficiently large to cause gate-oxide damage withinsecond amplification stage 120. -
FIG. 3 illustrates a schematic diagram of another embodiment of alevel shifter circuit 300.FIG. 3 shows an example embodiment of the impedance elements within a level shifter circuit, such aslevel shifter circuit 300. In particular,level shifter circuit 300 may include afirst impedance element 324, asecond impedance element 326, and athird impedance element 328 that are each formed by a pair of parallel-connected transistors. In one example, each is formed by an NFET device and a PFET device that are electrically connected in parallel as shown inFIG. 3 . The gate of each NFET device may be electrically connected tofirst power rail 140 and the gate of each PFET device may be electrically connected to second power rail 142 (e.g., ground). The resistance of each parallel-connected transistor may vary inversely proportional to the voltage value atfirst power rail 140. The impedance of the PFETs offirst impedance element 324 andsecond impedance element 326 may be determined by the voltage ofnodes second power rail 142. In such an example, when the output common mode is high that means the voltage ofnodes first impedance element 324 andsecond impedance element 326 and, thus, the voltage ofnodes first impedance element 324 andsecond impedance element 326 try to prevent the output common mode from going high. The impedance of the PFET ofthird impedance element 328 may be determined by the voltage ofnodes second power rail 142. When output swing is larger, the maximum voltage ofnodes third impedance element 328, which brings down the output swing. The PFET ofthird impedance element 328 may prevent the output swing from going high. Additionally, because the gates of each NFET device offirst impedance element 324,second impedance element 326, andthird impedance element 328 are connected tofirst power rail 140, which may vary, the strength at which each NFET device is turned on may vary and, thus, the resistance of each NFET device may vary inversely proportional to the voltage value atfirst power rail 140. In one example,first impedance element 324,second impedance element 326, andthird impedance element 328 may be variable resistance impedance elements for adjusting the signal amplitude and/or common mode atoutput signal nodes input signal nodes third impedance element 328 may have a characteristic that is similar to the PFET ofthird impedance element 328. More specifically, the impedance of the NFET ofthird impedance element 328 may be determined by the difference betweenfirst power rail 140 and the minimum voltage ofnodes nodes third impedance element 328 is small. This may prevent the output swing from going high. In such an example,level shifter circuit 300 may provide signal amplitude and/or common mode translation between, for example,first amplification stage 110 andsecond amplification stage 120 ofFIG. 1 , in order to ensure that the common mode ofoutput signal nodes second amplification stage 120 and/or that the signal amplitude is not sufficiently large to cause gate-oxide damage withinsecond amplification stage 120. -
FIG. 4 illustrates a schematic diagram of yet another embodiment of alevel shifter circuit 400.FIG. 4 shows an example embodiment of the impedance elements within a level shifter circuit, such aslevel shifter circuit 400. In particular,level shifter circuit 400 may include afirst impedance element 424, asecond impedance element 426, and athird impedance element 428. In one example,first impedance element 424 andsecond impedance element 426 may each be formed by a pair of parallel-connected transistors as shown inFIG. 4 and may be substantially identical in form and function tofirst impedance element 324 andsecond impedance element 326 oflevel shifter circuit 300, as described inFIG. 3 . However,level shifter circuit 400 ofFIG. 4 shows that the third impedance element, such asthird impedance element 428, may be formed of a pair of diode-connected transistors, such as a pair of diode-connected NFET devices. The diode-connected transistors ofthird impedance element 428 are always turned on, but the higher the voltage swing atoutput signal nodes third impedance element 428 decreases, which minimizes the variation of the output swing with respect to input swing. - In one example,
first impedance element 424,second impedance element 426, and the diode-connected transistor arrangement ofthird impedance element 428, each may be a variable resistance impedance element for adjusting the signal amplitude and/or common mode atoutput signal nodes input signal nodes level shifter circuit 400 may provide signal amplitude and/or common mode translation betweenfirst amplification stage 110 andsecond amplification stage 120 ofFIG. 1 , in order to ensure that the common mode ofoutput signal nodes second amplification stage 120 and/or that the signal amplitude is not sufficiently large to cause gate-oxide damage withinsecond amplification stage 120. -
FIG. 5 illustrates a schematic diagram of areceiver system 500, which is another example of a receiver system that includes a level shifter circuit for providing signal amplitude and common mode adjustment in an integrated circuit receiver.Receiver system 500 may include alevel shifter circuit 504, which may be another example embodiment oflevel shifting stage 130 ofFIG. 1 , that may be arranged betweenfirst power rail 140 and second power rail 142 (e.g., ground). Additionally,receiver system 500 may include a second amplification stage 506, which may be an example embodiment ofsecond amplification stage 120 ofFIG. 1 , that may be arranged betweenthird power rail 144 and second power rail 142 (e.g., ground). Additionally,receiver system 500 may include afeedback circuit 508, which is a negative feedback loop for providing fine control of the variable resistances of the first, second, and third impedance elements oflevel shifter circuit 504.Feedback circuit 508 may be connected tofirst power rail 140,third power rail 144, and second power rail 142 (e.g., ground). -
Level shifter circuit 504 may include a first, second, and third impedance element, such as described inFIGS. 2 , 3, and 4. In one example,level shifter circuit 504 may include afirst impedance element 524 and asecond impedance element 526 that may be formed of an NFET device and athird impedance element 528 that may be formed of a pair of diode-connected transistors, such as described with reference tothird impedance element 428 ofFIG. 4 .Input signal nodes first amplification stage 110 ofFIG. 1 . The signal amplitude and common mode atoutput signal nodes input signal nodes Output signal nodes transistors load 548 may be connected betweensignal output nodes third power rail 144. An opposite side oftransistors voltage node 550. Atransistor 552, which may be a constant current source element, may be connected betweenvoltage node 550 and second power rail 142 (e.g., ground). -
Voltage node 550 of second amplification stage 506 may be connected to the gate of atransistor 560 offeedback circuit 508. In one example,transistor 560 may include a PFET.Transistor 560 is electrically connected betweenfirst power supply 140 andsecond power supply 142. In an optional arrangement, a constantcurrent source element 562 may be connected betweenfirst power rail 140 and second power rail 142 (e.g., ground). Avoltage node 564 betweentransistor 560 andfirst power supply 140 drivesadjustable impedance elements 524 and 526 (e.g., by electrical connection with the gates oftransistors level shifter circuit 504 may be adjusted as a function offirst power rail 140. In another example, whenfirst power rail 140 is increased, the feedback loop pulls down the common mode ofoutput signal nodes - The common mode may be optimized with regard to
third power rail 144 and the current throughoptional transistor 552. More specifically,feedback circuit 508 optionally includes a mechanism for providing a common mode adjustment that is a function ofthird power rail 144. In particular,feedback circuit 508 may include a diode-connectedtransistor 570 betweenthird power rail 144 and second power rail 142 (e.g., ground), as shown inFIG. 5 . Optionally,circuit 500 may include aresistor 522. Avoltage node 574 at diode-connectedtransistor 570 may be connected to the gate oftransistor 552 of second amplification stage 506. In one example, diode-connectedtransistor 570 may provide dependence onthird power rail 144 to the common mode ofoutput signal nodes level shifter circuit 504. In such an example, whenthird power rail 144 increases the current throughtransistor 552 may increase (andvoltage node 550 may decrease), which may result in larger common mode ofoutput signal nodes level shifter circuit 504 andtransistors receiver system 500 may provide a common mode that tracks tothird power rail 144 and counter tracks tofirst power rail 140. In such an example, it may be ensured that the voltage atoutput signal nodes level shifter circuit 504 may not be sufficiently large todamage transistors - Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.
Claims (8)
Priority Applications (1)
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US12/241,935 US20090027124A1 (en) | 2007-01-15 | 2008-09-30 | Level-Shifting Buffer |
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US11/623,185 US7463078B2 (en) | 2007-01-15 | 2007-01-15 | Level-shifting differential amplifier |
US12/241,935 US20090027124A1 (en) | 2007-01-15 | 2008-09-30 | Level-Shifting Buffer |
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US11/623,185 Continuation US7463078B2 (en) | 2007-01-15 | 2007-01-15 | Level-shifting differential amplifier |
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US20090027124A1 true US20090027124A1 (en) | 2009-01-29 |
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US11/623,185 Expired - Fee Related US7463078B2 (en) | 2007-01-15 | 2007-01-15 | Level-shifting differential amplifier |
US12/241,935 Abandoned US20090027124A1 (en) | 2007-01-15 | 2008-09-30 | Level-Shifting Buffer |
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US8620707B1 (en) | 2011-06-29 | 2013-12-31 | Amazon Technologies, Inc. | Systems and methods for allocating inventory in a fulfillment network |
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US7463078B2 (en) * | 2007-01-15 | 2008-12-09 | International Business Machines Corporation | Level-shifting differential amplifier |
TW200913491A (en) * | 2007-09-11 | 2009-03-16 | Richtek Technology Corp | Level shift electric circuit |
US8976981B2 (en) | 2010-10-07 | 2015-03-10 | Blackberry Limited | Circuit, system and method for isolating a transducer from an amplifier in an electronic device |
US9093987B1 (en) * | 2012-09-28 | 2015-07-28 | Xilinx, Inc. | Differential level shifter for improving common mode rejection ratio |
US11114986B2 (en) | 2019-08-12 | 2021-09-07 | Omni Design Technologies Inc. | Constant level-shift buffer amplifier circuits |
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US6054888A (en) * | 1998-10-02 | 2000-04-25 | Advanced Micro Devices, Inc. | Level shifter with protective limit of voltage across terminals of devices within the level shifter |
US6396329B1 (en) * | 1999-10-19 | 2002-05-28 | Rambus, Inc | Method and apparatus for receiving high speed signals with low latency |
US6639427B2 (en) * | 2000-11-29 | 2003-10-28 | Stmicroelectronics Sa | High-voltage switching device and application to a non-volatile memory |
US7046067B2 (en) * | 2004-03-24 | 2006-05-16 | Taiwan Semiconductor Manufacturing Co., Ltd. | Thin-oxide devices for high voltage I/O drivers |
US20080169875A1 (en) * | 2007-01-15 | 2008-07-17 | International Business Machines Corporation | Level-Shifting Buffer |
-
2007
- 2007-01-15 US US11/623,185 patent/US7463078B2/en not_active Expired - Fee Related
-
2008
- 2008-09-30 US US12/241,935 patent/US20090027124A1/en not_active Abandoned
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US6054888A (en) * | 1998-10-02 | 2000-04-25 | Advanced Micro Devices, Inc. | Level shifter with protective limit of voltage across terminals of devices within the level shifter |
US6396329B1 (en) * | 1999-10-19 | 2002-05-28 | Rambus, Inc | Method and apparatus for receiving high speed signals with low latency |
US6639427B2 (en) * | 2000-11-29 | 2003-10-28 | Stmicroelectronics Sa | High-voltage switching device and application to a non-volatile memory |
US7046067B2 (en) * | 2004-03-24 | 2006-05-16 | Taiwan Semiconductor Manufacturing Co., Ltd. | Thin-oxide devices for high voltage I/O drivers |
US20080169875A1 (en) * | 2007-01-15 | 2008-07-17 | International Business Machines Corporation | Level-Shifting Buffer |
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US8620707B1 (en) | 2011-06-29 | 2013-12-31 | Amazon Technologies, Inc. | Systems and methods for allocating inventory in a fulfillment network |
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US20080169875A1 (en) | 2008-07-17 |
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