Does anyone know a good op-amp implementation of a "Valley Detector", which I assume would be what one calls the opposite of a peak detector? I need to find the baseline of a signal so I can reject it. I want to do an op-amp circuit instead of with a DAQ so I can do it in real time.
I'm dealing with DC signals, if that makes a difference. The "valley" is a positive nonzero voltage.
Probably, it's same with peak detector, only negative peaks instead of positive. Schem shown here, you need reverse diodes to make it register negative peaks.
Magician:
Probably, it's same with peak detector, only negative peaks instead of positive. Schem shown here, you need reverse diodes to make it register negative peaks.
Precision rectifier - Wikipedia
That won't work. There are no negative peaks. The minimum of the signal is nonzero and positive.
.. and the capacitor wired against Vcc..
There are no negative peaks.
Your "valley" is negative against your "hills" 
Can't find anything better:
http://s.eeweb.com/members/eugene_lisovy/answers/1357674786-AN1353.pdf
That won't work. There are no negative peaks. The minimum of the signal is nonzero and positive.
Negative compare to "virtual ground", which is 1/2 of power line for single power OPA circuitry in most cases.
What is the nature of the signal? Have you defined a time constants of detector?
Magician:
Can't find anything better:
http://s.eeweb.com/members/eugene_lisovy/answers/1357674786-AN1353.pdfThat won't work. There are no negative peaks. The minimum of the signal is nonzero and positive.
Negative compare to "virtual ground", which is 1/2 of power line for single power OPA circuitry in most cases.
What is the nature of the signal? Have you defined a time constants of detector?
I'm forced to use dual-supply on this circuit.
The nature of the signal is a photodiode, driven by a modulated laser on top of thermal IR.