Hawaslsh
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Hello,
I am trying to create a simple difference circuit using an op-amp (X-Y), but the output is not what I expect. The figure above is a simplified block diagram of the circuit. I am feeding two signals into a stand alone phase comparator, and I need to subtract the two output. In this case, R1 and Rf are equal at 1K for a gain of 1.
When I test the difference circuit alone, at DC it works as expected using variable power supplies. However, when I hook up the difference circuit into the circuit above, i get a strange result.
Ignore the yellow trace. The blue trace is the probing the D output directly out of the phase comparator. The Purple trace is probing the U output directly out of the comparator. The red trace is the Oscilloscope's own math function performing D-U. The green trace is the output from the difference circuit following the phase comparator. The math function (when not zero) calculates a value ~.75V. However, the output from the difference circuit is so small, and has such a large DC offset (>3V), that just to see any difference computation happening i had to AC couple the signal and move to 50mV / division. Why do you think my difference circuit is behaving this way?
Just a note on the phase comparator. The part number: MCK12140DG. Perhaps I should be buffering the inputs?
Thanks in advance,
Sami
I am trying to create a simple difference circuit using an op-amp (X-Y), but the output is not what I expect. The figure above is a simplified block diagram of the circuit. I am feeding two signals into a stand alone phase comparator, and I need to subtract the two output. In this case, R1 and Rf are equal at 1K for a gain of 1.
When I test the difference circuit alone, at DC it works as expected using variable power supplies. However, when I hook up the difference circuit into the circuit above, i get a strange result.
Ignore the yellow trace. The blue trace is the probing the D output directly out of the phase comparator. The Purple trace is probing the U output directly out of the comparator. The red trace is the Oscilloscope's own math function performing D-U. The green trace is the output from the difference circuit following the phase comparator. The math function (when not zero) calculates a value ~.75V. However, the output from the difference circuit is so small, and has such a large DC offset (>3V), that just to see any difference computation happening i had to AC couple the signal and move to 50mV / division. Why do you think my difference circuit is behaving this way?
Just a note on the phase comparator. The part number: MCK12140DG. Perhaps I should be buffering the inputs?
Thanks in advance,
Sami