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I want to measure 20 MHz signal by using microcontroller with 12 bit ADC And 200 Ksps sampling rate. Which circuit should I design in order to measure it accurately?

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    \$\begingroup\$ What aspect of it do you want to measure? How clean is it? What noise or interference do you need to ignore? What is the analog bandwidth of your ADC? Likely you want some kind of down conversion protected by filtering. Look at typical software defined radio designs. In some cases, if the analog bandwidth is sufficient you may be able to filter the RF range to avoid aliasing and then undersample, folding the downconversion right into the sampling itself. Also consider if what you want is more along the lines of a frequency counter than a receiver. \$\endgroup\$ – Chris Stratton Dec 17 '18 at 21:53
  • \$\begingroup\$ What aspect of it do you want to measure? => I want to measure volatge. How clean is it? => precise till uV. What is the analog bandwidth of your ADC? => I want to measure amplitude of fixed 20MHz sine wave. I want to detect the change in voltage in range of 10uV. \$\endgroup\$ – Kirtikumar Sonawane Dec 17 '18 at 21:55
  • \$\begingroup\$ What voltage? Average? Momentary? \$\endgroup\$ – Eugene Sh. Dec 17 '18 at 21:55
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    \$\begingroup\$ Depending on your need you may be able to build a frequency-insensitive RF power meter (basically a diode-type AM detector) and apply the ADC to the low-pass filtered output of that. \$\endgroup\$ – Chris Stratton Dec 17 '18 at 21:58
  • \$\begingroup\$ @EugeneSh. What voltage? Average? Momentary? => I want to measure it's peak value. and changes in peak value in 10uV of range. \$\endgroup\$ – Kirtikumar Sonawane Dec 17 '18 at 22:00
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MCU clocks do not have clean performance, that is they are very jittery. Use an off chip ADC with clean sample-convert clock.

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