The present invention teaches a system for selectably oscillating at a first or a second oscillating frequency. The system comprises an oscillator for providing an oscillating output. Moreover, the system comprises a switching device for selecting a first or a second impedance in response to a select...http://www.google.es/patents/US6225873?utm_source=gb-gplus-sharePatente US6225873 - Frequency shift key modulating oscillator
