Question

2. Consider the amplifier to the right. This is a common base amplifier Assume that the values of r ro, B, and gm, are known, or have bee found from the DC analysis. For the following questions, you have t show all steps of the circuit analysis. cC (a) Draw the small-signal version of this amplifier Include th Early effect resistance in the pi-model. In other words, the pi model should be: be To (b) Use the circuit of part (a) to derive an expression for the input resistance R, of this amplifier (at the (c) Derive an expression for the output resistance Ro of this amplifier (at the right arrow). Do not (d) Derive an expression for the voltage gain of this amplifier (Av -vo/vi). Do not ignore the Early Effect (e) Derive an expression for the following current gain: A e/i, where i, is the current at Ri flowing left arrow). Ignore the Early effect resistance ro for this part. ignore the Early effect resistance for this. resistance for this. from left to right, and ie is the current at Rg flowing downwards. Do not ignore the Early Effect resistance for this. Derive an expression for the acceptable signal (voltage) range of this amplifier for Vi (f)

Answer 1

COMMON BASE AMPLIFIER Input is applies to Emitter Output is served at the collector (a) Small - Signal version of the amplifier (b) Calculation of input resistance For calculation of output resistance we need to apply a voltage v_x at the input signal terminal and calculate the current i_x by the input Therefore R_in > v_x/i_x NOTE: Output port is kept open \r\n Circuit diagram for calculation of small signal input resistance Neglecting r_0 As we know that at E KCL must be satisfied And also see one terminal of r_pi is connected to ground and other terminal to E, an also for R_2 one terminal is connected to ground and other terminal to E. Therefore r_0 and R_2 are in parallel \r\n Therefore R_2/R_1 + R_2 middot v_x = (-v_pi) ----(1) At node (P) in the above figure KCL should be satisfied Therefore v_p = (-v_pi) Therefore i_x = -v_pi/R_2 parallel r_pi - 9m v_pi But -v_pi = (R_2 parallel r_pi)/R_1 + (R_2 parallel r_pi) v_x Therefore v_c = v_x (R_2 parallel r_pi)/R_1 + (R_2 parallel r_pi) [+ 1/R_2 parallel r_pi + 9m]

You can find io/iin using the following relationship vo = io*Ro and vin=iin*rin so by dividing all terms you can find the part e

I dont have any knowledge on part f

m so sorry

thanks for the question