WO2001015327A1

WO2001015327A1 - Transmitter equipment

Info

Publication number: WO2001015327A1
Application number: PCT/FI2000/000711
Authority: WO
Inventors: Arto Haapakoski
Original assignee: Nokia Networks Oy
Priority date: 1999-08-23
Filing date: 2000-08-22
Publication date: 2001-03-01
Also published as: AU6705500A; FI19991786A

Abstract

The invention relates to a method and equipment for increasing voltage in radio equipment employing the TDMA principle. The invention comprises a capacitive element (C) and two electronic switching elements (SW1), (SW2) controlling the charging and discharging of the capacitive element (C), the capacitive element (C) being connected in parallel with a direct current source (BATTERY) during the charging of the capacitive element (C), whereas when the capacitive element (C) is to be discharged, it is connected in series with the direct voltage source (BATTERY) to allow a substantially double voltage to be generated.

Description

TRANSMITTER EQUIPMENT

BACKGROUND OF THE INVENTION

The invention relates to the increasing of voltage in radio equipment, particularly in radio equipment employing the TDMA principle. Almost all GSM radio equipment (Global System for Mobile

Communication) use a single-cell 3.6V battery. The use of a 3.6V (lower voltage) battery and radio accessories would be the most economical choice also for other radio equipment employing the time division technique (TDMA, Time Division Multiple Access), such as radios of the new European open digital TETRA radio network (TErrestrial Trunked RAdio), because it would allow integrated high-volume GSM equipment circuits and additional high- volume GSM devices to be used.

The 3.6V voltage is not, however, sufficient for an RF transmitter (Radio Frequency) in the TETRA where the transmitter is required to offer both good linear properties and high output power at the same time. With current technology, TETRA radio equipment therefore has to be operated using a 7.2V battery with antenna powers of 1 and 3 watts.

In prior art solutions, voltage is increased by using charge pumps or choppers. Charge pumps are commonly used for generating the supply voltage for very low-power devices where the maximum load current may be about 200mA. The oscillator of the charge pump remains switched on all the time the output voltage is to be fed to the device using the voltage. A typical feature in charge pumps is that as the load increases, the output voltage decreases strongly, because it does not include stabilisation. The efficiency of a charge pump is usually 85%. Charge pumps used at high frequencies have smaller components, the filtering of disturbances being then easier than at low frequencies. However, a problem that arises when a continuously operating, high-power charge pump is used for increasing voltage in devices employing the TDMA principle is that during a TDMA transmission period, ripple emerges in the output voltage.

Choppers can be used for generating high voltages and currents, Choppers need an inductive component proportional to the output power, the component being the greater the higher the desired power. In addition, a capacitor and possibly a serial coil are needed for filtering the output voltage. The output voltage ripple mainly depends on the frequency of the chopper, the capacitance of the capacitor and the load current. As the load current increases, ripple increases, unless the chopper frequency or the capacitance of the capacitor is increased simultaneously. The ripple frequency components in the supply voltage of RF transmitters move to both sides of the transmission spectrum, thereby forming spurious emissions at the nearby area, i.e. within a distance of about 100 to 200 kHz and more from the carrier. The filtering of false transmissions is difficult, sometimes even impossible, and requires narrow-band, large and expensive RF filters, the use of which is generally avoided, if possible. For this reason, any ripple in the supply voltage is filtered, to the extent possible, before the RF transmitter. Due to internal series resistance in the battery, connector losses and pulse-like power consumption of the chopper, the chopper forms ripple and a spurious spectrum dependent on the chopper frequency also into the battery voltage. Ripple in battery voltage is harmful to all devices using battery voltage. To remove the ripple from the battery voltage, large, low-loss capacitors are needed, although otherwise their use is avoided, if possible.

In an optimum situation the chopper should be able to feed at least the power needed by an external device. Choppers usually have an efficiency of the order of 80-95%. Because of the inductive components they contain, choppers always cause electromagnetic disturbance to near-by devices and components. The disturbances are difficult to filter because choppers usually operate within a frequency range of 100 to 200 kHz. The filtering of low frequencies requires large filtering components and it is all the more difficult, the closer the devices affected by disturbance are to the chopper. Furthermore, if the operation of the chopper is based on pulse width modulation (PWM), false frequencies produced by the chopper have a wide spectrum.

BRIEF DESCRIPTION OF THE INVENTION It is an object of the present invention to provide equipment for increasing voltage in radio devices employing the TDMA principle. This object is achieved with a transmitter device comprising a direct voltage source, a radio transmitter for cyclic transmission, the transmitter requiring a supply voltage which is higher than said direct voltage, and means for generating said supply voltage from the direct voltage. The means are characterized in that they comprise a capacitive component; switching means which connect the capacitive component in parallel with the direct voltage source to charge the capacitive component between the transmitter's transmission periods and which connect the capacitive component in series with the direct voltage source during transmission periods, the voltage obtained as the sum of the direct voltage and the voltage of the capacitive component providing the supply voltage for the radio transmitter.

The invention also relates to a method for increasing voltage in equipment which employs the TDMA principle and in which the supply voltage required during active time slots is higher than the voltage of a direct current source, the method being characterized by comprising the steps of charging a capacitive component connected in parallel with the direct current source during inactive time slots; connecting the capacitive component in series with the direct voltage source during active time slots to generate a substantially double direct voltage for the supply voltage of the equipment. According to the basic idea of the invention, the direct voltage source is connected in parallel with the capacitive component during unused time slots (such as receive time slots) to charge the capacitive component, whereas during an active time slots (such as transmit time slots) it is connected in series with the capacitive component to obtain a substantially double voltage.

An advantage of the invention is that it allows a sufficiently high voltage with low disturbance to be generated for a device utilizing the TDMA. Another advantage is that the charging of the capacitive element takes place at an extremely high efficiency, almost 100%. In the invention, the charging of the capacitive component is controlled using the same control lines that are used for connecting the biasing of the output stage of a transmitter in a device employing the TDMA principle. This provides the advantage that the charging of the capacitive component coincides precisely with frame timing, which allows the effect of any coupling interference on the operation of a receiver or a frequency synthesizer, for example, to be automatically minimized. A further advantage of the invention is it reduces the costs of radio equipment and additional devices for radio equipment utilizing the TDMA principle because it allows lower battery voltages to be used. This also reduces the amount of power loss because the performance of modern signal processors and other baseband elements increases continuously, thereby requiring increasingly lower supply voltages to be generated in any case.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail in connection with preferred embodiments and with reference to the accompanying Figure 1 which is block diagram of transmitter equipment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Before a high-frequency, modulated signal RFIN that carries information and is to be inputted to an output stage is supplied to a filter FILTER and an antenna ANTENNA, the signal has to be amplified. As shown in Figure 1 , this power amplification takes place at a driver DRIVER and a power amplifier PA. However, since the RF output stage power amplifier PA employs the TDMA principle, the supply voltage VCC of 3.6V used in other parts of the transmitter is not sufficient for obtaining the required signal linearity and output power. For this reason the supply voltage must be increased to at least about 6 to 7 volts, the increased voltage being then supplied to the power amplifier PA as the supply voltage.

The voltage is increased using a charge pump VP of Figure 1 comprising two electronic switches SW1 , SW2 and a capacitive element C. The first electronic switch SW1 comprises a first and a second terminal and a control member, the second terminal of the switch SW1 being coupled to the direct voltage source VCC. The second electronic switch SW2 comprises a first and a second terminal and a control member, the first terminal of the switch SW2 being coupled to the first terminal of the first electronic switch SW1 , the second terminal of the switch SW2 being connected to substantially constant potential. The capacitive component C is arranged between the first terminal of the first electronic switch SW1 , the first terminal of the second electronic switch SW2 and the output of the charge pump.

The operation of the switches SW1 and SW2 is controlled using a line BIAS meant for controlling transmitter biasing so that when one switch is in position I, the other switch is in position II. The control of the switches SW1 and SW2 can also be implemented using a separate line.

The charge pump VP of the invention is operated by charging the capacitive component of the charge pump VP, such as the capacitor C, outside transmission time slots and by discharging it during transmission time slots by means of the switches SW1 , SW2. During the charging periods in a TDMA receive time slot, a switching signal from the control member guides the first switch SW1 to position I and the second switch SW2 to position II, the capacitive component being thereby connected in parallel with a direct voltage source BATTERY to charge the capacitive component to reach a direct voltage VCC. Also in a standby mode STBY, the capacitive component is connected parallel with the actual direct voltage VCC.

In a discharge period TX a switching signal BIAS from the control member guides the first switch SW1 to position II and the second switch SW2 to position I, the capacitive component C being thereby connected substantially in series with the direct current source BATTERY to generate a substantially double voltage V1=VCC+VC. The capacitance must be sufficiently high to ensure that the load current does not reduce the voltage V1 too much during the TDMA transmit time slot. The capacitive component may alternatively be a battery, provided that it can be used, i.e. charged and discharged, in all conditions, for example in extreme temperatures, and that the battery has sufficiently high capacity.

In Figure 1 the switches SW1 and SW2 are implemented as Metal Oxide Semiconductor transistors MOS, although other electronic structures may also be used. For example, one of the switches (SW1) may be replaced with a diode, provided that a decrease in the maximum output voltage equal to the diode threshold voltage is accepted. Other possible switching components include SOI, HEMT and HBT transistors, microwave tubes and vacuum tubes. The invention can also be implemented by applying bipolar technology alone. The voltage of the invention produced by the charge pump VP is particularly suitable for generating the output stage voltage for RF transmitters employing the TDMA principle, and it allows the voltage to be used as the supply voltage of a power amplifier and for obtaining sufficient dynamics in a cartesian linearization circuit of a TETRA transmitter, for example, and for broadband local oscillators of frequency synthesizers. In addition, switching implemented according to the principle of the invention can also be used for increasing the supply voltage of other radio parts.

The drawing and the related specification are only intended to illustrate the invention. The details of the invention may vary within the scope and spirit of the accompanying claims.

Claims

1. Transmitter equipment comprising a direct voltage source BATTERY; a radio transmitter for pulse-like transmission, the transmitter requiring a supply voltage which is higher than the direct voltage (VCC) of the direct voltage source; means for generating said supply voltage from the direct voltage (VCC), c h a r a c t e r i z e d in that the means comprise a capacitive component (C); switching means (SW1), (SW2) which connect the capacitive component (C) in parallel with the direct voltage source (BATTERY) to charge the capacitive component (C) between the transmitter's transmission periods and which connect the capacitive component (C) in series with the direct voltage source (BATTERY) during transmission periods, the voltage obtained as the sum of the direct voltage (VCC) and the voltage over the capacitive component (C) providing the supply voltage for the radio transmitter.

2. Transmitter equipment according to claim 1 , c h a r a c t e r i z e d in that the radio transmitter is a TDMA transmitter and that the switching means (SW1), (SW2) connect the capacitive component in series with the direct voltage source (BATTERY) during transmission time slots and in parallel side with the direct voltage source (BATTERY) during other time slots.

3. Equipment according to claim 1 or 2, c h a r a c t e r i z e d in that the switching means (SW1) and (SW2) comprise a first change-over switch (SW1), a first terminal of which is coupled to the direct voltage (VCC), a second terminal being coupled to a supply voltage terminal of the radio transmitter and to a first terminal of the capacitive component (C), and a third terminal of which is coupled to a second terminal of the capacitive component (C), the first reversing switch (SW1) being controlled in such a way that the first terminal is coupled to the third terminal during transmissions and to the second terminal during other periods; a second reversing switch (SW2), a first terminal of which is coupled to the second terminal of the capacitive component (C), a second terminal to a second supply voltage potential (GND), and a third terminal being a high-impedance terminal or an uncoupled one, the second reversing switch (SW2) being controlled in such a way that the first terminal is coupled to the third terminal during transmission periods and to the second terminal during other periods.

4. Equipment according to any one of claims 1, 2 or 3, characterized in that the direct voltage source (BATTERY) is a battery.

5. Equipment according to any one of claims 1, 2, 3 or 4, characterized in that the capacitive component (C) is a battery or a capacitor.

6. A method for increasing voltage in equipment which employs the

TDMA principle and in which the supply voltage required during active time slots is higher than the voltage (VCC) of a direct current source (BATTERY), characterized by comprising the steps of charging a capacitive component (C) connected in parallel with the direct current source (BATTERY) during inactive time slots; connecting the capacitive component (C) into series with the direct voltage source (BATTERY) during active time slots to generate a substantially double direct voltage for the supply voltage of the equipment.

7. A method according to claim 6, characterized in that the active time slots are transmission time slots of the TDMA transmitter.