ECE3110 Homework #9 Fall 2011

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1. Label the circuits below as Class A, Class B, or Class AB.

ECE3110 Homework #9 Fall 2011

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2. For Vsig=Vin=1+6sin(ωt)V and VDD=VSS=5V. Assume V1 (1a) is biased for correct operation. Assume

(1b) is biased at = 1. Sketch the output waveforms for all the circuits in Problem 1.

3. Calculate the efficiency for circuit 1b. Use = 1 and =10kΩ, VDD=VSS=5V.

=

= 14

= 14 4.8

110 4.85 = 11.5%

This is assuming a symmetric output and symmetric power supplies of equal value.

ECE3110 Homework #9 Fall 2011

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The output is not symmetric in this case. One way of getting the average is to take the rms value.

= ∗ = !"

∗

=#$ − #&'

√2 *

!"=

4.8 − 0.2√2

*

10 = 1.06,

Only one power supply of +5V:

- = ∗ = 1 ∗ 5 = 5

= -

= 1.065 = 21.2%

4. The datasheet of a bipolar transistor contains the following information:

Maximum allowable junction temperature TJmax = 100°C

Maximum power dissipation PDmax = 2 W at case temperature TC = 45°C

Junction-to-case thermal resistance θJC = 60 °C/W

Junction-to-ambient thermal resistance θJA = 100 °C/W

(a) What is the maximum case temperature to ensure safe operation at 0.2W?

(b) What is the case temperature when the transistor dissipates 500mW and the room is at 25oC.

ECE3110 Homework

For Problems 5-8. The above design uses

µpCox=60µA/V2, |VA|=40V. Neglect the effect of V

5. Fill in the empty spaces in the table above if A1=10V/V and the overall gain is A=200V/V.

6. (a) If C2=0.2pF, find the frequency of the second pole,

(b) Find the value of CC that results in

(c) Find the phase margin. Is the system stable

./*

.0 = 1 2#*3

PM=90 − tan89 :;:<=

− tan89 1:;:>

? where

PM=90 − tan89 1 @AAB9C9*B? − tan89 1@AA

C9D

Q (W/L) µCox (µA/V2) I(mA)

Q1 20 60 480E

Q2 20 60 480E

Q3 11 180 480E

Q4 11 180 480E

Q5 40 60 960E

Q6 10 180 960E

Q7 40 60 960E

Q8 40 60 960E

Homework #9 Fall 2011

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The above design uses ±5V power supplies. Let |Vt|=0.5V, µnCox=180

|=40V. Neglect the effect of VA on the bias currents. Use the following table:

Fill in the empty spaces in the table above if A1=10V/V and the overall gain is A=200V/V.

ind the frequency of the second pole, fp2.

that results in ft =300MHz.

Find the phase margin. Is the system stable?

* = F*2GH*

= 1.92G0.2I = 1,512KLM

1 #N3O

? H = 12#N*3:;

? = 9#*3@AAB = .53IQ

? where .R = 1 2B=*3O

? = 1 9.S#*3A.C@/? = 571KLM

1@AABC9DB? = 90 − 11 − 30 = 49 (STABLE!)

Vov(V) VGS(V) gm(mA/V) ro(kΩ)

0.9 1.4 1 83.3

0.9 1.4 1 83.3

0.7 1.5 1.4 83.3

0.7 1.5 1.4 83.3

0.9 1.4 2.2 41.7

1.03 1.5 1.9 41.7

0.9 1.4 2.2 41.7

0.9 1.4 2.2 41.7

=180µA/V2,

on the bias currents. Use the following table:

Fill in the empty spaces in the table above if A1=10V/V and the overall gain is A=200V/V.

IQ

ECE3110 Homework

The above design uses ±1.5V power supplies. Let

µpCox=60µA/V2, |VA|=15V. Neglect the effect of V

7. (a) Find the input common mode range and the range allowed for

(b) Fill in the empty spaces in the table above.

Homework #9 Fall 2011

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1.5V power supplies. Let IREF=300µA, |Vt|=0.7V, µnCox=180

|=15V. Neglect the effect of VA on the bias currents. Use the following table:

Find the input common mode range and the range allowed for vo.

Fill in the empty spaces in the table above.

=180µA/V2,

on the bias currents. Use the following table:

ECE3110 Homework #9 Fall 2011

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8. Find the overall gain of the op amp. Find A1, A2, and the dc open loop voltage gain.

ECE3110 Homework #9 Fall 2011

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9. What is the overall voltage gain if a load resistor is placed on the output, RL=2k.

10. (a) If C2=1pF, find the frequency of the second pole, fp2.

(b) Find the value of CC that results in ft =200MHz.

(c) Find the phase margin. Is this system stable? If not, how can it be made stable?