UNIVERSITY OF CALIFORNIA AT BERKELEY College of Engineering Department of Electrical Engineering and Computer Sciences EE105 Lab Experiments Prelab 7 Frequency Response Name Lab Section i t C v1 t v2 t A Figure 1 Amplifier with a Miller capacitor The Miller effect plays an important role in determining the poles of an amplifier If there is a gain A across the capacitor C as shown in Figure 1 the current across C can be written as d d v1 t v2 t C dt v1 t Av1 t i t C dt By distributing the derivative this simplifies to d i t C 1 A dt v1 t Therefore the equivalent capacitance looking into v1 t is the capacitance C multiplied by 1 A If the gain A is large enough this Miller effect can make the capacitor dominate and contribute to the dominant pole of the amplifier Using this same method you can derive the equivalent capacitance looking into v2 t which is C 1 1 A 1 For the common emitter amplifier shown in Figure 2 use the Miller approximation to derive the expressions for the two poles of vout vin in terms of C C gm RS r and ro These expressions will help you predict and understand the results of the lab 1 2 VCC 5 V RC 0 25 mA vOUT VBIAS vin RS Figure 2 Common emitter amplifier p1 p2 2 If RS 51 RC 10 k C 11 pF C 25 pF gm 3 mS r 10 k and ro 100 k what are the poles of this amplifier p1 p2 3 What will happen to the poles if a capacitor CM is added across the base collector junction 4 SPICE Construct the common emitter amplifier circuit shown in Figure 2 in SPICE Use VBIAS 0 58 V RS 51 and RC 10 k Use the 2N4401 SPICE model provided on the course website Perform an AC analysis of the circuit from 100 Hz to 10 GHz in HSPICE 3 Use Awaves to generate Bode plots both magnitude and phase for the circuit for vout vin Attach the Bode plots to this prelab worksheet Do the results agree with your hand calculations check the pole frequencies
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