frequency comparator

50 frequency comparator In the circuit described here, a refer- ence voltage level is derived from the comparison of the frequencies of two signals. Basically, the comparator has two input signals, one of which causes a capacitor to partly discharge while the other causes it to charge. The average charge on the capacitor (the desired reference level) will there- fore be a function of the frequencies of the two inputs. The "reference" capacitor is Cl in the circuit diagram. In the quiescent state the capacitor will be charged to half the supply voltage by the voltage divider con- sisting of R3 and R4. One input signal is fed to the base of T1 which switches on and off at the frequency of the input. There then follows what is commonly referred to as a "diode pump"! The action of this aptly named circuit is to produce a series of pulses that correspond to the frequency of the input signal. The pulses are used to control transistor T2 which proceeds to switch on and off thereby discha...