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I am trying to design the following schematics:

There are two kOhms resistance which are connected serially. One is load and another is device resistance. I need to apply the voltage in a the following way using IC switch

  • When voltage on the IC switch is non zero the voltage is applied only on the device

  • When it is zero the both R_load and R_device connected serially

Schematics

Since the signal through the resistance is a pulse with duration less than 100 ns I am using a couple of op-Amps for impedance matching (the measurements are carrying out on 1 MOhm oscilloscope channel). So I have to use fast IC switch.

For the first experiment I used constant voltage (~500 mV) applied on both resistance. I see the oscillations at the moment when switch is on or off. How can I remove these oscilltaions? I tried these schematics without op-Amps, and saw the same behaviour.

enter image description here

I tried on the several switches

  • ADG712
  • SN74LVC1G3157
  • SN74LVC1G66
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  • \$\begingroup\$ Show how you measure, that is, with a gnd antenna or properly low inductance \$\endgroup\$ – PlasmaHH Oct 11 '18 at 12:02
  • \$\begingroup\$ Sorry, I didn't get your question. I simply connected PCB to the oscilloscope, generator and power supply with coaxial cables and soldered wires respectively. \$\endgroup\$ – anatoly Oct 11 '18 at 12:40
  • \$\begingroup\$ Do these glitches also occur at the output of the buffer amplifier? You're switching its load, so it needs to react to that; unless it's very carefully compensated, you'd expect to see some sort of transient there. \$\endgroup\$ – Dave Tweed Oct 11 '18 at 12:45
  • \$\begingroup\$ I also tried these schematics without op-Amps, and saw the same behaviour. \$\endgroup\$ – anatoly Oct 11 '18 at 12:46
  • \$\begingroup\$ Do you have a 50-ohm termination on your oscilloscope? Many oscilloscopes have a switchable 50 ohm input mode. Otherwise you can use a feed through terminator. \$\endgroup\$ – τεκ Oct 11 '18 at 14:09

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