Rich D.
Active Member
Hi smart guys!
I am trying to breadboard a precision rectifier. It's end use is in an audio circuit, to drive a bar graph level meter. I have all the audio working fine, but for some reason I am continued to be stalled on this $%^&* rectifier circuit. See attached schematic.
What is puzzling is me is: I am using a Schottky diode in an op-amp feedback path. I am driving it with a 12-volt pk-pk sine wave signal at 2KHz, so I see both + and - 6 volt peaks on the input relative to ground. When I connect the first diode D1 only (cathode on output) I get a clean output signal - both + and - sides with no gain or level shift or rectification showing. But when I connect the other diode D2 only, the op-amp output goes to the negative rail and just refuses to budge. With both diodes in I get a clean signal with both polarities showing up on the output again. It appears to need D1 in there to prevent going negative rail, and it appears D2 has no effect whatsoever. Either way I am not seeing any rectified signal.
This is an over-simplified circuit I made to try to figure out what is going on with the op-amp and diodes. Eventually I expect to have a 10K resistor in series with the feedback diodes so they effectively sum their currents to the negative input. I will then tap the outputs thru the diodes to sum in the next op-amp stage. The negative peak is summed inverted but the positive peak is summed straight up, resulting in an output that is the desired "mmm" signal. When I do add those resistors and look for a 1/2 wave rectified signal, I don't see anything useful at all.
I hope to make a rectifier similar to one of the two diagrams I found on the inter-webs, also attached. That is of course if I can figure out why my rectifiers are not working.
What I did verify: Power is clean, stable +/-15V. 1uF decoupling at chip package. Note: not 0.1 uF, but 1.0 uF ceramics. Diodes test OK, about 350mV drop forward biased, open when reversed biased. Diodes rated for 40 volts. This particular Op amp works fine as a voltage follower, and I have several more of the same type in the circuit running audio from 20Hz to 100KHz. The other op-amp in the package is grounded as a voltage follower to reduce weird noise.
What could I be missing here?
I am trying to breadboard a precision rectifier. It's end use is in an audio circuit, to drive a bar graph level meter. I have all the audio working fine, but for some reason I am continued to be stalled on this $%^&* rectifier circuit. See attached schematic.
What is puzzling is me is: I am using a Schottky diode in an op-amp feedback path. I am driving it with a 12-volt pk-pk sine wave signal at 2KHz, so I see both + and - 6 volt peaks on the input relative to ground. When I connect the first diode D1 only (cathode on output) I get a clean output signal - both + and - sides with no gain or level shift or rectification showing. But when I connect the other diode D2 only, the op-amp output goes to the negative rail and just refuses to budge. With both diodes in I get a clean signal with both polarities showing up on the output again. It appears to need D1 in there to prevent going negative rail, and it appears D2 has no effect whatsoever. Either way I am not seeing any rectified signal.
This is an over-simplified circuit I made to try to figure out what is going on with the op-amp and diodes. Eventually I expect to have a 10K resistor in series with the feedback diodes so they effectively sum their currents to the negative input. I will then tap the outputs thru the diodes to sum in the next op-amp stage. The negative peak is summed inverted but the positive peak is summed straight up, resulting in an output that is the desired "mmm" signal. When I do add those resistors and look for a 1/2 wave rectified signal, I don't see anything useful at all.
I hope to make a rectifier similar to one of the two diagrams I found on the inter-webs, also attached. That is of course if I can figure out why my rectifiers are not working.
What I did verify: Power is clean, stable +/-15V. 1uF decoupling at chip package. Note: not 0.1 uF, but 1.0 uF ceramics. Diodes test OK, about 350mV drop forward biased, open when reversed biased. Diodes rated for 40 volts. This particular Op amp works fine as a voltage follower, and I have several more of the same type in the circuit running audio from 20Hz to 100KHz. The other op-amp in the package is grounded as a voltage follower to reduce weird noise.
What could I be missing here?