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Step of 6 2.065P Refer Figure P2.62 in the The expression for the common mode gain, of the differential amplifier is, = The worst case common-mode gain obtained when has maximum value Simplify the expression further Consider that all the resistors are The range is 100- 100+x 100-x R, Similarly, the range R, 100 100 100-x Step The maximum value of is obtained when the values of and are minimum. Select minimum R, values and to get worst-case common-mode gain. Substitute these values in the equation of to find the value of 1 100-x 100 100+x Rearrange the equation to find the value of 1 100- 100 = 200 100+ = 200 (100+x) Simplify the expression further 400x 200 2x = 100- 2x 100 50 Step of 6 Consider that the value of x=0.1 Calculate the worst case common-mode gain 50 0.1 - 50 =0.002 Consider that the value x=1 Calculate the worst case common-mode gain 50 - = 50 =0.02 Consider that the value x=5 Calculate the worst case mode gain 50 5 - 50 =0.1 Thus the values of worst case common-mode gain, for values of 1. and are 0.002 0.02 and Step The expression for the common mode rejection ratio, CMRR is, CMRR 20log Find the differential gain, assuming all the resistances are equal R The output voltage of differential amplifier using super position principle is, Substitute R for all resistance values. R R R Step 5 of 6 Therefore, the differential mode gain, is =1 Substitute for and in the expression for 50 1 CMRR M 50 50 Consider that the value 0.1 Calculate the common mode rejection 50 CMRR 20log 50 20log 0.1 =54 dB Step Consider that the value x=1 Calculate the worst-case common mode gain 50 CMRR 20log 50 1 =34 dB Consider that the value x=5 Calculate the worst case common-mode gain. 50 CMRR 20log 50 20log 5 =20(1) Thus, the values of common mode rejection ratio for values of and 5 are and