Fast peak detector requires special amplifier features. The output stage must have high slew rate to keep up with the intermediate stages of the amplifier. This condition causes either a long overload or DC accuracy errors. The amplifier must deliver large currents into the capacitive load of the detector to maintain a high slew rate of at the output. Other problems that should be resolved includes preservation of output voltage accuracy and instability with large capacitive loads.
With 50mA output current, 70° phase margin, and 450V/ms slew rate, LT1190 is suitable for this application. A 20W resistor (RO) isolates the 10nF load and prevents oscillation. Good accuracy is obtained using closed-loop peak detector circuit that employs a Schottky diode inside the feedback loop. The amplitude error of this circuit would be under 10% for the frequency up to 300 kHz of input signal, and under 20% for up to 3 MHz. [Schematic diagram source: Linear Technology Application Notes]