2
\$\begingroup\$

I'm designing a radar receiver, whose block diagram is below:

Radar receive path

When I compute power received from radar range equation, it varies between -90 dBm to -40 dBm depending on the object's location (60 to 6 meter).

After I downconvert frequency to 1-10 kHz range, the signal is still too weak so I'll need to amplify it once more so here's my question:

How much do I need to amplify the signal so that the input at ADC (say, 16-bit, Vref=1V) is 1 Vpp, not clipping and not too low so it's always properly detected?

I've used ADIsimRF and it looks like if I assume that I receive -90 dBm, I need to amplify the signal by 70 dB to get 200 mVpp, which means that if I receive -40 dBm, it will give me 54 Vpp.

Is there a way to anticipate how much power will I really be getting (say, 6 dBi patch antennas, radiated power is 12 dBm) or is there a way to know how much to amplify the signal?

\$\endgroup\$
2
\$\begingroup\$

The dynamic range of the signal is what it is and you cannot know beforehand if that signal is going to suddenly rise. You amplifiers and ADC have to cope with that dynamic range but often I've seen non-linear gain amplifiers used to reduce the dynamic range. ADI make a log amp that may be useful: -

enter image description here

\$\endgroup\$
  • \$\begingroup\$ Ok, it looks like I need to build Automatic Gain Control block, which is not as trivial as I thought. Thank you. \$\endgroup\$ – user1078719 Apr 2 '15 at 9:32
  • \$\begingroup\$ No, AGC is not what you want. AGC is driven by signal amplitude and it plays catch-up - it's fine for an AM receiver where the carrier doesn't change quickly but for radar the signal is there then gone in milliseconds. \$\endgroup\$ – Andy aka Apr 2 '15 at 10:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.