AD108 frequency multiplier capable of inputting asymmetric square wave

As shown in the figure, this is a frequency multiplication circuit that can input an asymmetric square wave. The characteristics of this circuit are: wide frequency range, not affected by power supply voltage changes, and can accept asymmetric input signals. When the input is a symmetrical square wave, the input signal is converted into a bipolar square wave after passing through a high-gain comparator and added to the integrator. The output of the integrator is a triangular wave. The triangular wave intersects with the zero line at T/4 and 3T/4 (T is the period of the input signal), and then the triangular wave is sent to the zero-crossing detector to obtain a square wave with a phase lag of 90o. The input signal and the output of the zero-crossing detector are sent to the two input terminals of the XOR gate to generate a frequency multiplication output. If the input signal is not a square wave or the input signal amplitude is greater than or less than the reference voltage VR, the output waveform of the comparator is an asymmetric square wave. In this case, if there is no feedback channel, the integrator will be saturated in one direction. Obviously, this cannot constitute a frequency multiplication output. However, after adding the feedback channel, since the average value of the output signal of the integrator is amplified by the feedback amplifier and sent to the " " input terminal of the integrator, the integrator will not be saturated, and its output is a symmetrical triangular wave. The integration time constant of the integrator can be determined according to the required operating frequency range. The output of the integrator should reach the power supply voltage value in 1/2 cycle of the lowest input signal frequency. Therefore, when the lowest frequency is 100Hz, the integration time constant is:

τ=RC=1/2×1/100=5ms

If the resistance R=10kΩ, the capacitor C should be 0.5μF.