UWEE538-Homework 2 Common-emitter Amplifier and Emitter Follower Solved

Problem 1: Common-emitter amplifier
 

For the following, use the figure and the simplified NPN model from Section 2.1.1 in AoE. VCC = 5V, C =

1µF, and  = 100. Use the npn Ltspice component for your simulations.

             

a)      Select values for RB1 and RB2 to achieve VB = 1V and a high-pass corner frequency (f3dB) of 10Hz. You may ignore base current for this step.

b)     Choose RC and RE for a gain of −10V/V (at 10kHz) and a collector current of 1mA. What is the DC value of VCE?

c)      Derive the transfer function for Vout/Vin and plot the frequency response (magnitude and phase) in MATLAB/Python.

d)     Perform an AC simulation of the circuit in Ltspice. Export the frequency response data for comparison to the ideal response from Part c (plot them together). Provide reasons for any discrepancies between the two.

 

 

 

Problem 2: Emitter follower 
 

 

 

                       Figure 2a. Emitter follower                       Figure 2b. Small-signal equivalent circuit
 

 

Use the Ebers-Moll model of the BJT and the figures to answer the following questions. VCC = 5V, IS = 10−16, and  = 100. When determining input/output resistances, connect a test voltage to the smallsignal circuit and determine the resistance as r = vtest/itest. Use the npn Ltspice component for your simulations.

 

a)      Design the biasing of the emitter follower (i.e. determine VB and RE) such that the collector current is 1mA and the DC level of Vout is 1V. You can do this by hand or use a MATLAB/Python script.

b)     Use the small-signal model (Fig. 2b) to determine the input resistance of the circuit. 

c)      Use the small-signal model (Fig. 2b) to determine the output resistance of the circuit. 

d)     Verify your design in Ltspice and include all relevant SPICE schematics and results in your submission.