| 摘要 |
<p>An oscillator 30 comprises a current supply 36 which supplies current to an inductive element and a capacitive element in a tank circuit 31, and to transistors 34 and 35. The capacitive element 33 has a variable capacitance for coarsely tuning the output signal frequency. Fine tuning is accomplished by varying the current supply 36. This is possible because of parasitic capacitances in the circuit. It is disclosed that a change in operating current causes a change in average bias voltage across the transistors 34 and 35, which leads to a change in parasitic capacitance. This is a combination of junction capacitance, which increases as average voltage decreases, and gate capacitance, which decreases as voltage decreases. It can be well defined for device geometry. Thus, a change in operating current can be used to vary the frequency of the LC tank 31. It is stated that tuning in this way can avoid the low Q that can result when a bank of capacitors is used, due to the circuitry required by the bank, which is not required in the present invention.</p> |
