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OPA615: use peak detector as positive valley detector

Part Number: OPA615
Other Parts Discussed in Thread: BUF602


I my application, I would like to detect the moment when a cutting tool touches a grounded part. This during cutting so depending on the cutting speed, the signal is very short. My first try was to use a NAND RS-latch with Schmidt triggers. The tool is connected with 1k pull-up resistor to 5V.

But tests show this is not fast enough Then I came accross the datasheet of OPA615. Figure 48 shows something which I think comes close to what I need, but I'm not sure. This circuit  should detect positive and negative pulses, but I assume negative here means lower then zero. I need the lowest positive value.

So, could somebody tell me if this circuit could be used to hold a 'positive valley', and if not how it can be adapted please?

Thanks in advance,

Best regards,


edit: picture added

  • Hi Marc,

    You should be able to use the above circuit for detecting the positive valley, especially the negative peak detection circuit through the BUF602 or -Vout path. The positive peak detection circuit or +Vout path can be configured instead in unity gain configuration by removing only the diode as shown below. Also, I believe the 27pF would need to be biased up to 1V or higher depending upon the diode drop needed to turn on and discharge the 27pF cap.

    Best Regards,


  • Thanks Rohit,

    I will try your suggestion and see what comes out.

    Best regards,