UWEE538-Common-emitter Amplifier and Opamp Nonidealities Midterm Solved

Problem 1: Common-emitter amplifier
 

For the following, VCC = 5V, VS = 1V, RS = 1k, Ibias = 100µA, RC = 10k, CL = 10pF,  = 100, VA = 100V, VT = 25mV, and IS = 10-16A. 

 

a)       Calculate the input impedance of the amplifier, Zin. Note: This does not include RS.

b)      Find an expression for the transfer function, Vout/VS. Be sure to account for attenuation due to Zin. 

c)       Calculate the DC gain and transit frequency fT.

                

Problem 2: Opamp nonidealities  
 



 

 

Assume the opamp has infinite gain and bandwidth. VOS = 1mV, and IB  = −1nA. Rf = 10Ri.

 

a)      Determine an expression for the output offset voltage, including the contributions from both VOS and IB.

b)      Assuming RS = 0, calculate values for Ri and Rf that result in zero output offset.

c)       Assuming RS = 1k and VOS = 0, calculate values for Ri and Rf  that result in zero output offset.

 

                


Problem 3. Opamp AC and transient analysis
 

 

             Figure 3a. Non-inverting amplifier   Figure 3b. Opamp open-loop frequency response
 



 

Figure 3. Input waveform for c) and d)

 

Assume ideal input/output resistances (Rin and Ro) for the opamp. Let Rf = 10Rin.

 

a)       Determine the DC gain and the 3dB frequency of the closed loop transfer function

(Vout/Vin).

b)      Provide an expression for the transient response of the amplifier for a voltage step input of 0 to 100mV. Sketch the response and label all relevant times/voltages.

c)       Assume the amplifier is driven by the input waveform shown in Fig 3c. Determine the minimum period T for which 0.1% settling is achieved during each half-period (integer multiples of T/2). Sketch the output waveform.

d)   Calculate the total worst-case error in the output voltage (at the end of each halfperiod) if the resistors have a tolerance of 0.1%.