The great gods of the peak detection circuit talk about the purpose of the two diodes, what changes have been made to the respective voltages at both ends, and what is the use of the final voltage fol

The great gods of the peak detection circuit talk about the purpose of the two diodes, what changes have been made to the respective voltages at both ends, and what is the use of the final voltage following? The circuit diagram you posted seems to be wrong. You should reverse the direction of D2, as shown in the figure below.

The function of D 1 is to form a sample-and-hold circuit together with C 1, which charges the peak voltage to C 1 when the input voltage reaches the peak value, and keeps the voltage on C 1 unchanged without being influenced by U 1 when the output voltage of U 1 drops with the input voltage after the peak value.

The function of D2 is to compensate the forward turn-on voltage drop of D 1 and make the voltage on C 1 equal to the peak input voltage of U 1.

U2 forms a voltage follower for impedance transformation. Because the input impedance of OPA37 is very high, the charge leakage on C 1 is greatly reduced, thus keeping the sampling voltage stable. Without this follower, the accuracy of the measurement results may be affected by the low input impedance of the measurement circuit.

The resistance of 1kω seems to be unnecessary, and it will not affect the function of the second-stage follower.