Circuits with Feedback Assignment Example | Topics and Well Written Essays - 1500 words

Circuits with Feedback - Assignment ExampleDerivation of Feedback Equation for Inverting Amplifier allow we librate an inverting amplifier as shown in fig. 2. Then if A, is the lay down and then, as vi+ = 0, there forrad vo = A(vin+ vin) vo = - A vinAlso from Ohms Law the certain is simply the difference in the voltage across R1 split R1, i1 = (vin+ vin)/R1 (5)Similarly,if = ( vi vo)/Rf (6)By Kerchiefs current Law at the inverting input,i1 = if + i where i is the current ingress the amplifier at its inverting point, yet for an idea amplifier it r to each onees to zero hence, i1 = if (7)Substituting the values from equations (5) and (6) we have, (vin+ vin)/R1= (vi vo)/Rf (8)Orvin+/R1 vin/R1= vi/Rf vo/Rf Solving for , = (9)This is the required voltage gain expression for inverting amplifier with feedback in call of open draw in gain.Problem 2 Each of the amplifiers shown below incorporate series feedback. The gains, input resistancesand getup resistances are quoted without feedback. For each amplifier determine -a) The feedback fraction.b) The gain with feedback.c) The input impedance with feedback.d) The output impedance with feedback.Solution (i) a) If we consider the given cct. then for feedback fraction , for given cct. is defined as,... terms of open-loop gain A. Derivation of Feedback Equation for Inverting Amplifier permit we consider an inverting amplifier as shown in fig. 2 (Bogart, 1997, p. 670). Then if A, is the gain then, as vi+ = 0, there fore vo = A(vin+ - vin) vo = - A vinFig. 2(a)Also from Ohms Law the current is simply the difference in the voltage across R1 separate R1, i1 = (vin+ - vin)/R1 (5)Similarly,if = ( vi - vo)/Rf (6)By Kerchiefs current Law at the inverting input,i1 = if + i where i is the current entering the amplifier at its inverting point, yet for an idea amplifier it reaches to zero hence, i1 = if (7)Substituting the values from equations (5) and (6) we have, (vin+ - vin)/R1= (vi - vo)/Rf (8)Orvin+/R1 - vin/R 1= vi/Rf - vo/Rf Solving for ,= (9)This is the required voltage gain expression for inverting amplifier with feedback in terms of open loop gain.Problem 2 Each of the amplifiers shown below incorporate series feedback. The gains, input resistancesand output resistances are quoted without feedback. For each amplifier determine -a) The feedback fraction.b) The gain with feedback.c) The input impedance with feedback.d) The output impedance with feedback.Solution (i) a) If we consider the given cct. then for feedback fraction , for given cct. is defined as, = (2ia)Substituting the values in equation (2ia) from given cct. we have, == 0.175 2ia Fig. (2i)(2ib) If Avf, be the gain