| 摘要 |
A wide-band, voltage controlled oscillator is described which has a frequency range of six decades. The voltage controlled oscillator (VCO), which uses complementary metal oxide, semiconductor field effect transistor elements (C-MOS-FET's), is basically an astable multivibrator which is operated from a voltage controlled, variable amplitude, constant current source. The constant current source includes a p-channel MOS-FET operated in a saturated mode to provide a constant current which may be selectively varied as a function of the gate to source voltage. The current source is coupled to a capacitor storage element through a pair of C-MOS-FET's which selectively establish a conducting path between the capacitor and the constant current source to charge and discharge the capacitor. The C-MOS-FET elements through which the capacitor charges and discharges are controlled by a C-MOS-FET switch means which is actuated in response to the voltage level on the capacitor. By utilizing a constant current source to charge the capacitor, linear charging is easily achieved. Furthermore, the rate at which the capacitor is charged, and hence, the oscillator frequency, may be readily varied over a wide range of values by varying the current level as a function of the input voltage applied to the gate of the constant current p-channel MOS-FET. In one example, a VCO is described which is capable of operating over a frequency range from 5 Hz to 5.5 MHz, and may, in one application described herein, form part of a Phase Locked Loop which is capable of operating over a dynamic frequency range of five decades, i.e., 50 Hz to 5 MHz.
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