Comparator unexpected output in pspice

Discussion in 'Homework Help' started by justinjunghkim, Feb 17, 2015.

  1. justinjunghkim

    Thread Starter New Member

    Dec 23, 2014
    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

  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    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.
    Last edited: Feb 18, 2015