precision diode using OPA277

Akhilesh,

Two minor changes will make a dramatic change in your simulation:

Change the diode to 1N4148. The 1N1183 is a slow rectifier diode that does not recover fast enough when reverse biased.

Change the op amp to OPA132. The OPA277 is a bipolar op amp with clamp diodes between the two inputs. This diodes conduct when the input is negative and feed a signal to the output.

Regards, Bruce.

Sir I have done it. For some range of output resistance this circuit is working satisfactorily. But i have tested this circuit under condition" input : voltage 50milivolt sinusoidal signal with 50Hz frequency. the output of such a input signal is as follows :

Sir why this circuit is not showing rectification behavior ?

Akhilesh,

The differential input capacitance of the op amp is coupling the input signal directly to the output on negative half-cycles. Make R1=10k and this effect is minimized.

Regards, Bruce.

for R1=10k the performance is good. But if I increase the value of value of R1 in range of mega ohm, it is not working properly. Sir why the value of R1 is going to affect the rectification behavior of the circuit ?

Akhilesh,

For negative inputs the diode is reverse-biased. The output of the op amp is essentially disconnected from the output node that you are measuring. In fact, the output of the op amp swings to the V- power supply while the input is negative. R1 is required to hold the measured output at 0V as this output node could otherwise be influenced through the differential input capacitance of the op amp. R1 serves to "pull down" the output node to 0V. If this resistance too high, it cannot hold the output to 0V.

Regards, Bruce.