Hi all,

I have a difficulty to have an expected output of my comparator opamp. It was very strange, because I used same circuit structure before, and it worked perfectly fine, but after changing some parameters, I keep getting a zero output. I don't know what happened to my schematics. I was guessing that it is because LM324 characterlistic...? I looked up the datasheet, but couldn't find anything.

here is basic information of my design. Please find an attached file for the reference.

Im using opamp LM324
highpass filter is set to be 23kHz
Vinput: Voff = 0V; Vamp = 300mV; Freq = 50kHz Green scope
Vbias = 1.14V (input bias after filter) Red scope
Vreference = 1.2V (comparing voltage) Yellow scope
Vdd = 3.7V
output of opamp Blue scope

Thank you in advance!

Best Regard

Justin

 

Look up the Gain Bandwidth Product and Slew Rate for an LM324. You need an opamp with a GBP of at least 10Mhz (or a real comparator) to do what you are attempting to do...

Also the LM324 may not even operate on only 3.7V.