Electronics II
Single-stage IC Amplifiers
Single-Stage IntegratedCircuit Amplifiers
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
1
Single-stage IC Amplifiers
Electronics II
Outline
• Comparison between the MOS and the BJT
• From discrete circuit to integrated circuit
- Philosophy, Biasing, …etc.
• Frequency response
• The Common-Source and Common-Emitter amplifier
with active loads
• The Common-Gate and Common-Base amplifier
with active load
• The Source and Emitter Follower
• The CS and CE amplifier with source degeneration
• Current mirrors with improved performance
• Cascode amplifier and transistor pairings
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
6-1 Comparison between the MOS and the BJT
DC characteristics
• Transconductor (iD - vGS v.s. iC - vBE )
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
• Channel-length modulation (iD - vDS ) v.s. Early effect (iC – vCE)
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Low-frequency operation
• Input resistance
• Transconductance
⎛W ⎞
g m = 2( µ nCox )⎜ ⎟ I D
⎝L⎠
gm =
IC
VT
• Output resistance
• Intrinsic gain
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Single-stage IC Amplifiers
Electronics II
High-frequency operation
• Cutoff frequency
fT =
gm
2π (C gs + C gd )
2
For C gs >> C gd and C gs ≅ WLCox
3
1.5µVOV
fT ≅
2πL2
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
fT =
gm
2π (Cπ + Cµ )
For Cπ >> Cµ and Cπ ≅ Cde
fT ≅
2 µVT
2πW 2
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Trends in IC technology
• Technology speed figure of merit v.s. Time:
• Estimated frequency performance based on scaling
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Single-stage IC Amplifiers
Electronics II
Comparison
From analogue or digital point of view?
BJT
MOS
DC range of operation
>5 decades of
IC ∝ eVBE
2-3 decades of
ID ∝ (VGS –VT )2
Small-signal output resistance ( ro )
Slightly larger
Smaller for short
channel
Cutoff frequency ( fT )
100GHz
50GHz
Switch implementation
Poor
Good
Less 1/f
More 1/f
Voltage dependent
Reasonably good
Noise (thermal about the same)
Capacitor implementation
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
6-2 From Discrete- to Integrated- circuit
Components
(The pictures are copied from http://140.114.23.141/htdocs/course/922_EE226002/Introduction.pdf , S.H. Hsu)
Hsin Chen, 2005
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Electronics II
Single-stage IC Amplifiers
Hardware products
(The pictures are copied from http://140.114.23.141/htdocs/course/922_EE226002/Introduction.pdf , S.H. Hsu)
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Design topologies
• Active load to replace R
R=?
• Current biasing
• Direct-coupled
ÆDifferential architecture to
decouple DC signals (Ch7)
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
IC Biasing – current mirror (amplifier)
• Io / IREF =
• Minimum Vo =
• Effect of ro :
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Current steering
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Single-stage IC Amplifiers
Electronics II
BJT current mirror
• Io / IREF =
• Minimum Vo =
IO
I REF
=
1+
m
m +1
β
• Effect of ro :
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Single-stage IC Amplifiers
Electronics II
6-3 Frequency response
• In analysing the frequency response of circuits,
capacitors Æ 1/sC
inductors Æ sL
T ( s) =
m −1
am s + am −1s + L + a0
s n + bn −1s n −1 + L + b0
m
Vi(s)
T(s)
Vo(s)
Substituting s=jw into T(s) Æ The gain and phase response v.s. w
T ( s ) = am
( s − Z1 )( s − Z 2 ) L ( s − Z m )
( s − P1 )( s − P2 ) L ( s − Pn )
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Zeros :
Poles :
Hsin Chen, 2005
Single-stage IC Amplifiers
Electronics II
Bode plot
| T (s) |
a pole T ( s ) =
∠T (s )
1
s + p0
a zero T ( s ) = s + z0
How about positive-valued poles/zeros?
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Example
T (s) =
10s
(1 + s / 10 2 )(1 + s / 105 )
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Example- continued
T (s) =
10s
(1 + s / 10 2 )(1 + s / 105 )
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Single-stage IC Amplifiers
Electronics II
High-frequency response
• Frequency response of a direct-coupled amplifier
FH ( s ) =
(1 + s / z1 )(1 + s / z 2 ) L (1 + s / z n )
(1 + s / p1 )(1 + s / p2 ) L (1 + s / pn )
We are mostly interested in 3-dB frequency, fH (or f3dB)
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Single-stage IC Amplifiers
Electronics II
Methods to derive fH
• If a dominant pole exists
FH ( s ) ≅
1
1 + s / wP1
• If not, use the cond. |F(wH)| = ½ to derive
wH ≅ 1
⎛ 1
1
1 ⎞ ⎛ 1
1
1 ⎞
⎜⎜ 2 + 2 + L + 2 ⎟⎟ − ⎜⎜ 2 + 2 + L + 2 ⎟⎟
wPn ⎠ ⎝ wZ 1 wZ 2
wZn ⎠
⎝ wP1 wP 2
• Open-circuit time constants
wH ≅
1
∑ Ci Rio
i
Rio : resistance seen by Ci when all other Cs are open-circuit
and all sources equal zeros
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Example 6.6
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Single-stage IC Amplifiers
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Miller’s theorem – one useful technique for analysing freq response
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Example 6.7
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Single-stage IC Amplifiers
Electronics II
6-4 Common-Source and Common-Emitter
amplifers with acitive loads
Common-source amplifier
Ri =
Avo =
Ro =
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Common-source amplifier with active load
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
• Large-signal characteristics
• Small-signal characteristics (in region III)
Rin =
Av =
Rout =
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
• High-frequency response
(i) Analysis by Miller’s Theorem
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
(ii) Analysis by Open-circuit time constants
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
(iii) Exact analysis
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005
Electronics II
Single-stage IC Amplifiers
Formulas for Common-Emitter amplifier with active load
c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith
Hsin Chen, 2005