Lect. 17: Two-Stage Amplifier
Qualitative analysis of two-stage transconductance amplifier
Current Mirrors
Differential Amp
Frequency Compensation
CS Amp
GND
Electronic Circuits 2 (17/1)
W.-Y. Choi
Lect. 17: Two-Stage Amplifier
Input Common-Mode Range
For VCM,min, Q1, Q2 should be in saturation
VSD1 > VSG1 - |VTH,p|
VS1 – VD1 > VS1-VCM - |VTH,p|
VCM > VD1- |VTH,p|
VCM,min = VGS3 - |VTH,p|
For VCM,max, Q5 should be in saturation
VSD5 > VSG5 - |VTH,p|
VS5 – VD5 > VS5-VG5 - |VTH,p|
VD5 < VG5 + |VTH,p| = VDD – VSG5 + |VTH,p|
Large I  Large VSG5, VSG1, VGS3
 Small input CM range
Electronic Circuits 2 (17/1)
VCM+VSG1 < VDD – VSG5 + |VTH,p|
VCM,max= VDD – VSG5 –VSG1 + |VTH,p|
W.-Y. Choi
Lect. 17: Two-Stage Amplifier
Voltage Gain (DC)
Two CS amps in cascade
Gm1=
R1=
Av1 =
Gm2=
R2 =
Equivalent Circuit
Av2 =
Av=
Rin:
Rout:
Electronic Circuits 2 (17/1)
W.-Y. Choi
Lect. 17: Two-Stage Amplifier
Frequency Response
For simplicity, assume all the capacitive elements
are lumped together as C1 and C2.
Electronic Circuits 2 (17/1)
W.-Y. Choi
Lect. 17: Two-Stage Amplifier
Vo ( s )
?
Vid ( s )
 P ,in ~
P 2 ~
1
1
~
R1 C1  (1  Gm 2 R2 )CC 
R1Gm 2 R2CC
1


1 
R2  1 
 CC  C 2 
G
R
m2 2 


~
1
R2  CC  C 2 
Reduce CC for bandwidth enhancement
Why do we need CC?
Electronic Circuits 2 (17/1)
W.-Y. Choi
Lect. 17: Two-Stage Amplifier
Design Project #1 (Due May 4. Details available in tera.yonsei.ac.kr)
Two-stage OTA (Operational Transconductance Amplifier)
Electronic Circuits 2 (17/1)
W.-Y. Choi