frequency response of amplifier
DESCRIPTION
Frequency Response of Amplifier. Input signal of an amplifier can always be expressed as the sum of sinusoidal signals. The amplifier performance can be characterized by its frequency response. Frequency response of a linear amplifier. Amplifier Transmission or Transfer Function. - PowerPoint PPT PresentationTRANSCRIPT
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Frequency Response of Amplifier
• Input signal of an amplifier can always be expressed as the sum of sinusoidal signals.
• The amplifier performance can be characterized by its frequency response.
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Amplifier Transmission or Transfer Function
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• The figure indicates that the gain is almost constant over a wide range of frequency range ω1 to ω2 .
• The band of frequencies over which the gain of the amplifier is within 3dB is called the amplifier bandwidth.
• The amplifier is always designed so that its bandwidth coincides with spectrum of the input signal (Distortion less amplification)
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Amplifier Transfer Function• Amplifier Types
– Direct Coupled or dc amplifier– Capacitively Coupled or ac amplifier
• Difference– Gain of the ac amplifier falls off at low frequencies
• Amplifier gain is constant over a wide range of frequencies, called Mid-band
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• Evaluate the circuit in Frequency Domain by carrying out the circuit analysis in the usual way but with inductance and capacitance represented by their reactances– An inductance L has a reactance or impedance jωL and Capacitance C
has a reactance or impedance 1/jωC
• The circuit analysis to determine the frequency response can be in complex frequency domain by using complex frequency variable ‘s’– An inductance L has a reactance or impedance sL and Capacitance C
has a reactance or impedance 1/sC
Frequency Response of DC Amplifier
Figure 6.12 Frequency response of a direct-coupled (dc) amplifier. Observe that the gain does not fall off at low frequencies, and the midband gain AM extends down to zero frequency.
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A resistively loaded MOS differential pair
It is assumed that the total impedance between node S and ground is ZSS,
consisting of a resistance RSS in parallel with a capacitance CSS.
CSS includes Cbd & Cgd of QS as well as Csb1 & Csb2.
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Differential Half-circuit.
Frequency Response: Differential Gain
Frequency Response is the same as studied earlier for common source amplifier.
Microelectronic Circuits - Fifth Edition Sedra/Smith
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Figure 6.20 High-frequency equivalent-circuit model of the common-source amplifier. For the common-emitter amplifier, the values of Vsig and Rsig are modified to include the effects of rp and rx; Cgs is replaced by Cp, Vgs by Vp, and Cgd by Cm.
Microelectronic Circuits - Fifth Edition Sedra/Smith
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Figure 6.23 Analysis of the CS high-frequency equivalent circuit.
Microelectronic Circuits - Fifth Edition Sedra/Smith
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Figure 6.24 The CS circuit at s 5 sZ. The output voltage Vo 5 0, enabling us to determine sZ from a node equation at D.
Quiz # 3 (Syn A)Determine the short circuit transconductance (Gm) of the given circuit.
Quiz # 3 (Syn B)Determine the short circuit transconductance (Gm) of the given circuit.
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Common-mode half-circuit.
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Common-mode half-circuit.
D
D
SS
Dcm R
RRRA
2
SSSSD
D
SS
D
D
D
SS
Dcm RsC
RR
RR
RR
ZRA
1
22
SSSS
SSSSSSSS RsC
RCRZ1
||
Acm has a zero on the negative real-axis of the s-plan with frequency ωz
SSSSz
SSSSz CR
fCR p
2
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Figure 7.37 Variation of (a) common-mode gain, (b) differential gain, and (c) common-mode rejection ratio with frequency.
SSSSSS
D
SS
Dcm RsC
RR
ZRA 1
22
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Figure 7.37 Variation of (a) common-mode gain, (b) differential gain, and (c) common-mode rejection ratio with frequency.
SSSSSS
D
SS
Dcm RsC
RR
ZRA 1
22
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Figure 7.38 The second stage in a differential amplifier is relied on to suppress high-frequency noise injected by the power supply of the first stage, and therefore
must maintain a high CMRR at higher frequencies.
Exercise 7.15
Microelectronic Circuits - Fifth Edition Sedra/Smith
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Figure 6.22 Application of the open-circuit time-constants method to the CS equivalent circuit of Fig. 6.20.
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Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier.
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Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier.
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Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier.
mm
idm
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2
3
3
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1
22
m
m
idm
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gmd
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2
3
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m
m
m
idm
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Lo
o
Lout
Lout CsR
RsC
RRsC
rrR
1
1||1|||| 00402
Lo
m
m
idom CsR
gCs
vRgV
11
1
12
3
0
3
3
1
21
11
m
m
m
m
Loomd
gCs
gCs
CsRRgA
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Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier. (b) The overall transconductance Gm as a function of frequency.
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0201 & rrNeglect
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idm
g sCg
vgV
33
2
3
3
4344
1
22
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m
idm
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idmm
gmd
gCs
vg
sCg
vggVgI
21
2
3
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m
m
idm
ddvg
gCs
vgIII
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Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier. (b) The overall transconductance Gm as a function of frequency.
Lo
o
Lout
Lout CsR
RsC
RRsC
rrR
1
1||1|||| 00402
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2
3
0id
m
m
m
idm vg
gCs
vgI
Lo
m
m
idom CsR
gCs
vRgV
11
1
12
3
0
3
3
1
21
11
m
m
m
m
Loomd
gCs
gCs
CsRRgA
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Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier. (b) The overall transconductance Gm as a function of frequency.
3
3
1
21
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m
m
m
m
Loomd
gCs
gCs
CsRRgA
L1 C of valuelarge todue poleDominanat 2
1
Lop CRf
p
omRgGainMidband
m
mp C
gfp2
32
m
mz C
gfp2
2 3
The zero frequency (fz) is twice that of the pole (fp2)
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Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier. (b) The overall transconductance Gm as a function of frequency.
Lop CRf
p21
1
omRgGainMidband
m
mp C
gfp2
32
m
mz C
gfp2
2 3
Assignment # 4
• Carry out detailed frequency response analysis of the current-mirror-loaded MOS differential pair circuit.
• Due date: 2 Dec 2011