I have a radar motion sensor, IPM-170.

The output of the sensor is as follows: The AC motion signal is -+300uv and there is a DC bias around 150mv.

I am applying the following circuit so I can run my sensor in the pulse mode.

When T2 goes to the saturation, the IF signal (DC bias + AC motion signal) goes to the amplifier. However, that high value of DC bias (150mv) enters my amplifier as a step input (a lot of frequencies) so it passes the DC blocking capacitor and it takes a long time to decay throughout the output of the two stages op-amps. Also, my AC signal would not be, of course, recognized during my limited ON period of the transistor.

How can I completely block that DC bias signal from the sensor?

Two stage amplifier for Radar motion sensor running in pulse mode enter image description here

  • \$\begingroup\$ T2's emitter has no DC connection so what is the intention of that part of the circuit and where did the idea for T2's role come from? \$\endgroup\$
    – Andy aka
    Oct 1, 2019 at 11:59
  • \$\begingroup\$ I have got this circuit from the application note. As I understand the role of T2 is to pass/band the signal of IF through the ON/OFF periods. \$\endgroup\$
    – mmyname
    Oct 1, 2019 at 12:03
  • \$\begingroup\$ BTW, this isn't "pulsed radar". It's CW radar that you happen to be turning on and off at regular intervals. \$\endgroup\$
    – Dave Tweed
    Oct 1, 2019 at 12:12
  • \$\begingroup\$ It's OK to be CW because I am running two radar motion sensor next to each other and I want them to run alternatively in order not to have an interference in the received path. I am just using the concept of pulsing the power supply. \$\endgroup\$
    – mmyname
    Oct 1, 2019 at 13:03


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