Complementary Folded Cascode OpAmps for Low Voltage ...

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Complementary Folded Cascode
OpAmps for Low Voltage Applications
U. Kleine and F. Roewer
Otto von Guericke University
Magdeburg

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Motivation
Introduction
Example MOS Folded-Cascode
Folded Cascode OpAmp
- Output Swing
- Poles and Zeros
Complementary Folded-Cascode
Folded Cascode OpAmps
- 3 Novel Structures
- Measurement Results
Conclusion

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One Stage
OpAmp
Unity gain frequency
DC-Gain DC
Motivation
gm
f 0 =
2 C
Gain A 0 = gm r01
1

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Output Resistance
MOS Folded-Cascode OpAmp
Vout = Vdd – |VTp VTp|
- 2 Vov
Vout = -Vss Vss
+ 2 Vov
Output Resistance R out = { (ro2
|| ro12
) + ro2A
[ 1+
( g m2A + g mb2A )( ro2
|| ro12
) ] } || { ro4
+ ro4A
[ 1+
( g m4A + g mb4A )( ro4
) ] }

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A
0
= g
= g
= g
DC-Gain DC Gain
m2
m2
m2
ω
= C
1
R
out
Poles and Zeros
{ (ro2
|| ro12
) + ro2A
[ 1+
( g m2A + g mb2A )( ro2
|| ro12
) ] } || { ro4
+ ro4A
[ 1+
( g m4A + g mb4A )( ro4
) ] }
{ r ( g + g )( r || r ) } || { r ( g + g )( r ) }
o2A
m2A
First Pole
1
≈ C
1
R
out
mb2A
o2
o12
o4A
m4A
mb4A
{ r ( g + g )( r || r ) } || { r ( g + g )( r ) }
o2A
m2A
mb2A
o2
o12
o4A
m4A
mb4A
o4
o4

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U -
I
B1
U
Common Mode Voltage Range
(J.H. Huijsing und D. Linebarger)
UDD
U
a
R R
U
SGp
1 2
dsat
U
+
U
U
U
dsat
SGp
CM
U
U
U
CM
GSn
dsat
U
U
R R
3 4
U
U - U +
dsat
GSn
a
USS
I
B2
U
U
DD
SS

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Rail-to-Rail-Difference Stage

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First Novel Structure with Rail-to-Rail Input Stage

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Small Signal Quantities of the First Amplifier
Asymmetric Current Mirrors
I
I
D, M7
D, M8
DC Gain
i
out, a
=
v
WM6
WM6
I bias I bias I bias WM6
= I D, M6 − I D, M4 = I D, M3/5 − I D, M4 = ⋅ − = ⋅ −1
W
W 2 2 2 W
M5
WM9
WM9
I bias I bias I bias WM9
= I D, M9 − I D, M2 = I D, M1/10 − I D, M2 = ⋅ − = ⋅ −1
W
W 2 2 2 W
diff
2
⋅
© ©
g
m, M1/M2
⋅
A
M10
V0
1+
g
=
m, M10
v
v
out
diff
g
+ g
=
i
m, M9
out
ds, M10
v
⋅ r
diff
+ g
out
ds, M1
M5
M10
+ g
m, M3/M4
⋅
1+
g
£ ¤ £
m, M5
¥
£ ¤ £
¥
M5
g
+ g
M10
m, M6
ds, M5
+ g
¢
¡
¢
¡
ds, M3
¦ § ¦
¨

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Small Signal Quantities of the First Amplifier (2)
Simplified DC Gain
A
V0, a
1
2
1+
Poles and Zeros
A
V, a
=
⋅
(p) =
C
P =
g
1
2
⋅
2
m7
W
W
1+
⋅ C
⋅ g
M6
M5
4
W
W
m8
⋅
(g
⋅ p
M6
M5
2
ds, M6
g
C
+
+ g
m, M7
⋅
P ⋅ C
§ ¨ §
©
2
l
⋅ g
g
¤¢¥
ds, M4
+ g
g
g
) ⋅ g
mb, M7
p ⋅ C
(g
⋅ p +
m7
¦
m7
+ C
⋅ g
m8
m, M1/M2
2
4
m8
ds, M7
+ 1
ds, M6
⋅ g
+ g
m8
©
+ g
g
+
⋅ g
§ ¨ §
g
ds, M4
m7
m, M3/M4
ds, M8
⋅ p + 1
g
m, M1/M2
) ⋅ g
⋅ ( g
m, M8
+
ds, M7
ds, M9
+ g
p ⋅ C
g
m7
+ g
mb, M8
4
g
+
ds, M2
+ 1
ds, M8
©
)
⋅ g
§ ¨ §
⋅ ( g
m, M3/M4
ds, M9
g
m8
+ g
£
¢¡
ds, M2
)

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Second New Amplifier

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Small Signal Quantities
Proper Operation Point with 0 < ID,M21 ID,M21
= ID,M22 ID,M22
< 0.5 IBIAS
A
V0, b
V, b
=
g
ds, M7
⋅ ( g
l
ds, M6
g
m, M7
Poles and Zeros
A
(p) =
g
P ⋅ C ⋅ p +
P =
i out, b ≈ v diff ⋅ ( g m, M1/M2 + g m, M3/M4 )
+ g
+ g
ds, M7
g
ds, M4
C
mb, M7
p ⋅ C
g m8
⋅ (g
2
m7
⋅ C
⋅ g
g
+ g
2
ds, M6
4
m8
m, M1/M2
ds, M21
+ 1
+ g
g
⋅ p
m7
2
©
+ g
) g
+
⋅ g
§ ¨ §
ds, M4
C
+
m, M3/M4
ds, M8
m, M1/M2
2
+ g
⋅ g
g
+
⋅ ( g
ds, M21
m7
m7
+ C
⋅ g
ds, M9
g
m, M8
+ g
+ g
ds, M2
mb, M8
p ⋅ C 4
+ 1 ⋅ g
g m7
) g ds, M8 ⋅ ( g
+
4
m8
⋅ g
m8
©
§ ¨ §
⋅ p + 1
+ g
m, M3/M4
ds, M9
ds, M22
+ g
g
m8
)
ds, M2
+ g
ds, M22
)

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Third New Amplifier

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Proper Operation Point Current
i
out, c
Poles and Zeros
A
=
V, c
v
diff
2
Small Signal Quantities
⋅
¤ ¤ ¤ ¤ ¥ ¤
¦
g
m, M1/M2
+ g
l
⋅
m, M3/M4
m8
⋅
p ⋅ C
g
(p) =
g
P ⋅ C ⋅ p +
P =
g
C
2
m7
£ ¤ £
¥
⋅ C
⋅ g
4
m8
1+
g
2
ds, M7
⋅ p
1+
g
+ 1
2
m, M10
⋅ (g
m, M5
⋅ g
ds, M6
g
C
+
¢
¡
2
m7
+ g
+ g
m, M1/M2
⋅ g
g
ds, M10
+ g
g
m7
m7
ds, M5
+
m, M9
g
£ ¤ £
ds, M4
+ C
⋅ g
+ g
m8
m, M6
+ g
ds, M1
ds, M3
+ g
+ g
ds, M21
ds, M22
p ⋅ C 4
+ 1 ⋅ g
g m7
) g ds, M8 ⋅ ( g
+
g
4
¥
⋅ g
m8
⋅ p + 1
¢
¡
m8
§ ¨ §
ds, M9
©
§ ¨ §
m, M3/M4
©
£
¡
+ g
ds, M2
)

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First Pole
Gain Bandwidth
Product
Gain Bandwidth Product
GBW
f
=
1
=
A
2
V0
1
⋅ r
⋅ f
1
out
≈
⋅ C
g
L
m, M1/M2
2
+ g
⋅ C
m, M3/M4
L

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Chip Microphotograph of the Third Folded-Cascode
Amplifier

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Chip Microphotograph of the First Folded-Cascode
Amplifier

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Chip Microphotograph of the Second Folded-
Cascode Amplifier

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Gain (dB)
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
Frequency Response of the OpAmps
1,E+02 1,E+03 1,E+04 1,E+05 1,E+06 1,E+07 1,E+08
Frequency (Hz)
0
-15
-30
-45
-60
-75
-90
-105
-120
-135
-150
-165
-180
Phase (°)
Gain a (dB)
Gain b (db)
Gain c (db)
Phase a (°)
Phase b (°)
Phase c (°)

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Gain (dB)
Frequency Response of the OpAmp for Different
Bias Current
80
70
60
50
40
30
20
10
0
-10
1,E+02 1,E+03 1,E+04 1,E+05 1,E+06 1,E+07 1,E+08
Frequency (Hz)
0
-20
-40
-60
-80
-100
-120
-140
-160
-180
Phase (°)
Gain@100µA (dB)
Gain@200µA (dB)
Gain@300µA (dB)
Phase@100µA (°)
Phase@200µA (°)
Phase@300µA (°)

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VDD DD = 5V,
C1 = 5pF
Differential
gain AV0
Differential
GBW
Phase Margin
ϕ
Power
dissipation
Input offset
voltage
Slew rate
(rise/fall)
Input noise @
10kHz
CMRR
Ibias bias = 150µA
(V/V)
(MHz)
(°)
(mW)
(mV)
(V/µs)
(nV/√ (nV/ Hz)
(V/V)
Performance Table
Opamp a)
81,5 dB
20,5
68,5
3,9
-1.5 1.5 .. 5.6
-5,8/6,6 5,8/6,6
18,0
>60dB
Opamp b)
69,5 dB
21,5
77,5
3,8
-4.9 4.9 .. 3.5
-4,9/3.5 4,9/3.5
17,3
>51dB
Opamp c)
70,5 dB
21,8
78,2
4,1
-4.7 4.7 .. 1.8
-4,8/1.8 4,8/1.8
17,0
>51dB

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VDD DD = 5V,
C1 = 5pF
Input voltage
range
Output
voltage range
Size (length *
width)
Ibias bias = 150µA
(V)
(V)
(µm²)
Performance Table (2)
Opamp a)
0.0 .. 5.0
0.7 .. 4.3
143 * 103
Opamp b)
0.0 .. 5.0
0.6 .. 4.4
149 * 103
Opamp c)
0.0 .. 5.0
0.6 .. 4.4
148 * 103

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Conclusions
➤Three Three Different Folded-Cascode
Folded Cascode Amplifiers
➤Rail Rail-to to-rail rail input range
➤Power Power supply voltage range: 2.5V-5V 2.5V 5V
➤Bandwidth Bandwidth 100MHz@1pF Load, 20MHz@5pF
➤Compact Compact layout by use of module generator
➤Applications: Applications: SC circuits, DA / AD converter ...
➤Published Published in J. SSC August 2002