Ele591I E-Testing II
Final Exam

5/9/2000

Question 5
  1. Bipolar Parameters
     
    npn
    pnp
    Units
    Is
    6E-17
    7E-16
    Amps
    VAF
    325
    90
    Volts
    beta
    100
    75
     
    MOS Parameters
     
    NMOS
    PMOS
    Units
    KP
    30E-6
    10E-6
    Amps/V2
    Vth
    2
    -1.25
    Volts
    Lambda
    0.02
    0.02
    V-1
    Vt = KT/q = 0.0257 Volts at room temperature.

    Table I

      Design a 10uA Widlar current source using the transistors described in Table I.

    What is the output impedance?
Answer
Use bipolar transistors.

Pick an Iref and R that satisfies the equation.

Vt ln[Iref/Io] = R*Io

R = (Vt/Io) ln[Iref/Io]

Also,

Rout = ro[1+gmRe]

Re = R

Rout = (VAF/Io)[1+(Io/Vt)R]

Possible answers
Iref
R
Rout
20 uA
1.78K
55MEG
27.2 uA
2.57K
65MEG
50 uA
4.14K
84MEG
100 uA
5.9K
107MEG
200 uA
7.7K
130MEG
500 uA
10K
160MEG
1 mA
11.9K
182MEG