Half-wave synchronous detection circuit composed of switching circuit

An analog switch is used to alternately turn the input signal on and off, and a low-pass filter smoothes the pulsating current
(pulsation is removed and becomes DC). The OP amplifier Ai is a buffer amplifier , which is opposite to the input resistance of the low-pass filter
behind it , and the output resistance must be very small.     If the DC blocking capacitor C is not added, the error or drift caused by the DC offset of the front stage will affect the performance of the circuit. The selection of the capacity should ensure that the impedance is small enough for the signal frequency. 6     OP amplifier A2 is a zero-crossing comparator, so it should be selected Ic with fast conversion speed, otherwise phase lag will occur. When the reference input contains noise, a certain hysteresis (positive feedback) should be added. The port signal waveform is based on a sinusoidal transition. If the TTL level can be used, a C-MOS analog switch can be used to simplify the switching circuit composed of Trlz .