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Saturday, October 10, 2009

Open Loop Fast Peak Detector Circuit

This is a design schematic for fast peak detector similar but faster than previous peak detector, can be implemented using open loop configuration. This circuit is based on LT1190 IC for operation. This is the figure of the circuit.

In this circuit, operation is begun from D1 is the detector diode and D2 is a level shifting or compensating diode. A load resistor RL is connected to – 5V and an identical bias resistor, RB, is used to bias the compensating diode. This equal value resistor is RL and RB makes sure that the diode drops are equal. Low values of RB and RL (1k to 10k) yield in fast response, at the expense of poor low frequency accuracy. High values of RB and RL provide good low frequency accuracy but cause the amplifier to slew rate limit, resulting in poor high frequency accuracy. A solution can be made by adding a feedback capacitor CFB, which improve the negative slew rate on the (–) input. We can expect is under 15% amplitude error for 2Vpp-6Vpp input at 20MHz, much faster than closed loop design. [Schematic diagram source: Linear Technology Application Notes].

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