1. 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.

2. Frequency response of a linear amplifier
Amplifier Transmission or
Transfer Function

3. Amplifier Bandwidth
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)

4. 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

5. Evaluating the Frequency Response
of Amplifier
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

6. Frequency Response of DC Amplifier
Figure 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.

7. A resistively loaded MOS differential pair
sedr42021_0736a.jpg
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.

8. Differential Half-circuit. Frequency Response: Differential Gain
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Frequency Response is the same as studied earlier
for common source amplifier.

9. Microelectronic Circuits - Fifth Edition Sedra/Smith
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Figure 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

10. Microelectronic Circuits - Fifth Edition Sedra/Smith
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Figure Analysis of the CS high-frequency equivalent circuit.
Microelectronic Circuits - Fifth Edition Sedra/Smith

11. Microelectronic Circuits - Fifth Edition Sedra/Smith
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Figure The CS circuit at s 5 sZ. The output voltage Vo 5 0, enabling us to determine sZ from a node equation at D.
Microelectronic Circuits - Fifth Edition Sedra/Smith

12. Quiz # 3 (Syn A)
Determine the short circuit transconductance (Gm) of the given circuit.

13. Quiz # 3 (Syn B)
Determine the short circuit transconductance (Gm) of the given circuit.

14. Common-mode half-circuit.
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15. Common-mode half-circuit.
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Acm has a zero on the negative real-axis
of the s-plan with frequency ωz

16. Figure Variation of (a) common-mode gain, (b) differential gain, and (c) common-mode rejection ratio with frequency.
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17. Figure Variation of (a) common-mode gain, (b) differential gain, and (c) common-mode rejection ratio with frequency.
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18. Figure 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.
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19. Exercise 7.15

20. Microelectronic Circuits - Fifth Edition Sedra/Smith
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Figure Application of the open-circuit time-constants method to the CS equivalent circuit of Fig
Microelectronic Circuits - Fifth Edition Sedra/Smith

21. Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier.
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22. Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier.
sedr42021_0739a.jpg

23. Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier.
sedr42021_0739a.jpg

24. Figure 7.39 (a) Frequency-response analysis of the active-loaded MOS differential amplifier.
sedr42021_0739a.jpg

25. Figure (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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26. Figure (a) Frequency-response analysis of the active-loaded MOS differential amplifier. (b) The overall transconductance Gm as a function of frequency.
sedr42021_0739a.jpg

27. The zero frequency (fz) is twice that of the pole (fp2)
Figure (a) Frequency-response analysis of the active-loaded MOS differential amplifier. (b) The overall transconductance Gm as a function of frequency.
sedr42021_0739a.jpg
The zero frequency (fz) is twice that of the pole (fp2)

28. Figure (a) Frequency-response analysis of the active-loaded MOS differential amplifier. (b) The overall transconductance Gm as a function of frequency.
sedr42021_0739a.jpg

29. Assignment # 4
Carry out detailed frequency response analysis of the current-mirror-loaded MOS differential pair circuit.
Due date: 2 Dec 2011