Hughes Papers: Sample Questions 4 - 5 of 19

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Question number: 4

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Considering the analog signal 3cos200t, determine the minimum sampling rate required to avoid aliasing.

Explanation

  • Nyquist criteria says that if we want to transmit any signal through the channel without any type of distortion, then sampling frequency should be at least twice or greater then signal frequency.
  • If signal frequency is fc and sampling frequency is fm then,
  • If this criteria is not fulfilled then aliasing effect will take place where, signal will not be received as it was transmitted from the transmitter side and lower frequency components will be irretrievably lost.
  • Here, the given signal is 3cos200πt,
  • Comparing it with the general sinusoidal signal,

s (t) = Acos2πft

A = 3 and 2f = 200

So, f = 100 Hz

  • So, to avoid aliasing Nyquist criteria should be fulfilled.

Question number: 5

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What is CMRR regarding Op-Amp?

Explanation

  • CMRR stands for Common Mode Rejection Ratio. It is a measure of ability of op-amp or any instrument to reject interference which is common to both input terminals. It can be defined as ratio of differential mode gain to the common mode gain.
  • Ideally common mode gain of the amplifier is 0 if both the inputs are identical and differential gain is infinity. So, CMRR has to be infinite ideally. It is expressed in decibels.
  • CMRR =
  • CMRR (dB) = 20 log