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I'm trying to design a circuit that "multiplies" two signals.

I have an electrical unit with two separate circuits. One circuit drives the other one with a square signal. The width of the square signal is on the order of milliseconds. The amplitude can be set anywhere between 0 V and 10 V. The input resistance of the second circuit is 10 kΩ.

I would like to "multiply"/chop this signal with an LVTTL control signal. The width of the LVTTL can be as low as 50 ns. The amplitude is ~2 V. I want to pass the original signal if the control signal is high (2 V) and set it to zero if the control signal is low (0 V).

So far, I have tried to use a two-stage n-type MOSFET but the output dips to -0.5 V for a short time at the rising edge of the LVTTL signal. I tried different loads and stuff but did not get any good output.

  1. Do you know any circuit that does what I need?
  2. I have a buffer circuit, do I need it?
  3. How to avoid the negative potentials on the rising edge of the LVTTL signal?

I can upload my LTSplice circuit if you want, or you can direct me to the right discussion group.

Here are images from LTSpice: The 1st graph outlines my circuit, the 2nd, and the 3rd graphs show my input signal and my LVTTL control signal. The 4th and 5th graphs show output signals vs different input amplitudes. The 6th graph shows the signal at the output of the first MOSFET. The last two images show the outputs vs the stage 1 signal (output of the first MOSFET) This is my cirucit Original Signal from 1st box Thisis my control signal-LVTTL

Control Signal vs Output1 Control Signal Vs Output2 Control vs STage1 1stSTage Vs Output1 1St stage vs Output2

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    \$\begingroup\$ The negative dips might be artefacts of ineffective scope probing after all, what would cause negative voltages. Also, draw a block diagram and or picture of the output waveforms. \$\endgroup\$
    – Andy aka
    Jan 25, 2020 at 19:15
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    \$\begingroup\$ hi, this sounds interesting. A schematic really can't hurt. By the way, this sounds like a classical chopper mixer – an architecture that is proven to work, well above the 20 MHz square wave that your 50 ns implies :) Thinking about your -0.5 V, those might be probing artifacts (as Andy says), but also actual inductive effects on your board itself, so a photo to go with the schematic would be most helpful. \$\endgroup\$
    – Marcus Müller
    Jan 26, 2020 at 0:30
  • \$\begingroup\$ Hello, I have screenshots showing of my circuit and signals at multiple places. I donot know how to upload images to this site. When I find it out, I will post them. \$\endgroup\$
    – u c coskun
    Jan 26, 2020 at 23:49

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