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I'm currently working on a project to build a portable logic analyzer. There will be 4 input channels to the design, however I was highly recommended to redesign this using a differential input to isolate noise.

So far, each input channel gets scaled for the ADC max. voltage of 3.3V and has a zener diode for current limiting.

Can anyone recommend a specific differential input IC or circuit to apply to my current schematic layout?

enter image description here

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    \$\begingroup\$ Why are you using an analog to digital converter for a LOGIC analyzer? You should be using a comparator to convert from analog to digital, unless you are sampling really slow inputs. \$\endgroup\$
    – crj11
    Nov 7, 2019 at 2:51
  • \$\begingroup\$ We plan on implementing the comparator through the adc essentially. \$\endgroup\$ Nov 7, 2019 at 3:23

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The esp32 is capable of 27.2 ksps or 27kHz, so just about any instrumentation amplifier or operational amplifier would be fine for the purpose of subtracting channels, especially since the gain will probably be reduced to the 3.3V scale.

The best thing to do would be to use a comparator stage after the instrumentation amplifier with a low noise DAC to set the reference for the comparator.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ I think yours is the better advice -- most especially the instrumentation opamp configuration. Personally, I think the OP should perhaps learn some skills applying cheap devices like this, which is under $25 and can provide about 100 MHz sampling rates after the comparator you show. (Well, some thought to the front end beyond what you write is obviously needed.) Cheap and very, very powerful, then. \$\endgroup\$
    – jonk
    Nov 7, 2019 at 3:22
  • \$\begingroup\$ @jonk Thanks, I agree an ESP32 is probably not the device to build an logic analyzer around, building it with an FPGA would be a very fun project. You could probably feed the data into the ESP32 and transmit it wirelessly if it supported the bandwidth. A lot of cheap logic analyzers also use cirrus logic SOC devices \$\endgroup\$
    – Voltage Spike
    Nov 7, 2019 at 4:16

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