ECE 342 Solve problem 3 and 4

ECE 342 Problem Set #9

Due: 5 P.M. Wednesday, October 28, 2015

Fall Semester 2015 Prof. E. Rosenbaum Prof. T. Trick

Reading Assignment: Sections 6.6.3, 6.6.4, 6.6.6, 5.6.6

1. Consider the circuit shown below,

(a) Find Gv (vout/vsig) for IBIAS values of 0.1, 0.2, 0.5, 1 and 1.25 mA.

(b) Why isn’t Gv a linear function of IBIAS?

(c) For IBIAS = 1mA, what is the maximum allowed value of Vsig, where vsig = Vsig*sin( t)? The circuit must provide linear amplification.

vsig ∞

VCC

vout ∞

IBIA S

RB=480kΩ

-VEE

RL=100kΩ

∞

Rsig=10kΩ

RC=10kΩ

ß = 100

VA=25V

2. Consider the circuit shown below,

(a) Choose the value of Re such that Gv is maximized, subject to the constraint that vbe ≤ 10mV and the transistor stays in the active mode. What is the value of Gv?

(b) If β drops by 10%, what is the new value of Gv? All other design variables are unchanged.

vsig=0.05sin(ωt) ∞

+5V

vout ∞

0.2mA

100kΩ

20kΩ

∞

20kΩ

20kΩ

ß = 100

VA=∞

Re

-5V

10V

-10V

3. Find Rin, Rout, Gv, and the overall current gain io/isig (“Gi”). You are given that β=100 and VA=∞. VBE,ON = 0.7V.

100kΩ

vsig ∞

5V

-5V

3.3kΩ 2kΩ

vo

io

ii

4. Choose the value of IBIAS such that vout is a sinusoidal signal with amplitude 200 mV or larger.

5V

10kΩ

vout

75Ω

∞ vsig=0.5sin(ωt)

VIN=3V IBIAS

ß = 100

VA=∞

5. Consider the circuit shown below,

(a) Find the dc bias point and small-signal model parameters. Assume λ = 0.

(b) Find Rin, Rout, Avo and Gv.

(c) Repeat part (b) for the case that λ = 0.03. You will have to recalculate ro.

(d) Finally, you will consider the body effect; i.e., you will no longer assume that V B = VS but, instead, that VB = -VSS, which is -5V in this circuit. You are given γ = 0.4V

1/2 and 2ϕF = 0.6V. You may

assume λ = 0 for simplicity. First, you need to recalculate the dc bias point. You may iteratively

solve for VS and Vt, using

( )

and (√ √ ).

Do not iterate more than 2 or 3 times, as this should be sufficient to obtain the value of V t with less than 10mV error. Then, redraw the small-signal model, now including the gmb current source shown in Fig. 5.62 of the textbook. The value of gmb can be found using equations (5.110) and (5.111). You are to calculate the value of Gv.

1MΩ

vsig

∞

5V

5kΩ

vout 4.7MΩ

-5V

∞

0.5mA

Vto=0.75V

k=2mA/V 2