40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  PSL  Not logged in ELOG logo
Entry  Thu Apr 25 20:24:27 2019, anchal, Summary, Electronics Equipment, Adjustable TTL Trigger Generator Box Adjustable_TTL_Trigger_Generator_Box.pdf
    Reply  Sun Apr 28 22:29:18 2019, rana, Summary, Electronics Equipment, should I use an OpAmp as a Comparator? 
       Reply  Tue Apr 30 18:55:06 2019, anchal, Summary, Electronics Equipment, Follow up on TTL Trigger generator box 
Message ID: 2332     Entry time: Tue Apr 30 18:55:06 2019     In reply to: 2329
Author: anchal 
Type: Summary 
Category: Electronics Equipment 
Subject: Follow up on TTL Trigger generator box 

But I used AD620 which is an instrumentation amplifier, not opamp. I thought comparators are made with differential amplifiers (from Horowitz & Hill Sec 4.23) and since AD620 was a nice available instrumentation amplifier, I thought it would work (and it does work).

But this particular circuit that I made seems to be less general than I thought. 100 kOhm potentiometer makes it hard to fine tune the threshold. Also, I think I should have buffered the threshold voltage divider circuit because I see the threshold level changing with the incoming signal when the signal is more than the threshold. It doesn't affect my particular application, but I think that makes this a crappy TTL generator. But since my purpose has been served, I'll push optimizing and generalizing this box to some other day. Maybe my new SMD prototype boards would be handy.

Quote:

not all amps are good for use as a comparator

https://www.analogictips.com/faq-use-op-amp-comparator/

 

ELOG V3.1.3-