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I'm using sensitivity time controlled (STC) pin diodes of PN:MPP 4201A-206 for our applications. Our operating frequency from 1300 MHz to 1400 MHz.

See the schematic diagram below. As device functionality suggested for below cases:

  1. If we apply the voltage at 0.84 V from DAC output (all bits are high) to attenuate 42 dB but we measured incorrectly at 10 dB attenuation.
  2. If we apply the voltage at 0 V from DAC output (all bits are low) to attenuate 0 dB but we measured correctly at 0 dB attenuation.

We are not getting the expected results for full attenuation when DAC output at 0.84 V so nearly 32 dB difference is noticed.

Can anyone please suggest if this circuit implementation is correct? Is there anything we missed?

Kindly give your suggestion. Let us know if you have any questions.

schematic diagram

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  • \$\begingroup\$ Are you sure you're using these PIN diodes the right way? These are basically current controlled resistors. If you're trying to use them as a switch, they have to be driven with relatively high currents, 100 mA. \$\endgroup\$
    – SteveSh
    May 12, 2022 at 11:35
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    \$\begingroup\$ 0.84 volts won't drive very much current into those shunt diodes, especially with R24 in the way. 10 dB attenuation sounds entirely reasonable. Why do you think it should be 42 dB? Link to the app note that says it should, or the data sheet for the device. Why are two diodes grounded via 100 ohm resistors and the rest taken directly to ground? Have you got lambda/4 length of track between the diodes (practical given your very narrow bandwidth)? This improves the attenuation of an all-shunt attenuator significantly. \$\endgroup\$
    – Neil_UK
    May 12, 2022 at 12:44

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