EECS 105 Spring 2002 Lecture 26
R. T. Howe
Lecture 26
• Last time:
– Finish methods for finding two-port model
parameters
– Start common-source amplifier
• Today :
– Current-source supplies
– Common-gate amplifier
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
Non-Ideal Current Sources
We want to have both RD and a very large gm at the same
time … how to do it?
The gain depends on the small-signal resistance; the DC
current can be set by a supply ! modify load line
ISUP
resistor
VSUP
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
Current Source Supply
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
Common-Source Amplifier with
Current Source Supply
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
Load Line for DC Biasing
Both the I-source and the transistor are idealized for DC bias analysis
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
Two-Port Parameters
From current
source supply
Rin =
Gm =
Rout =
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
P-Channel CS Amplifier
DC bias: VSG = VDD – VBIAS sets drain current –IDp = ISUP
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
Two-Port Model Parameters
Small-signal model for PMOS and for rest of circuit
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
Common Gate Amplifier
DC bias:
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
CG as a Current Amplifier: Find Ai
iout = id = - ig – is= -it
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
CG Input Resistance
At input:
Output voltage:
Dept. of EECS
University of California at Berkeley
EECS 105 Spring 2002 Lecture 26
R. T. Howe
CG Output Resistance
Dept. of EECS
University of California at Berkeley