1. Chapter 10 Analog Systems
Microelectronic Circuit Design
Richard C. Jaeger
Travis N. Blalock
Microelectronic Circuit Design, 3E
McGraw-Hill

2. High-pass Amplifier: Description
True high-pass characteristic impossible to obtain as it requires infinite bandwidth.
Combines a single pole with a zero at origin.
Simplest high-pass amplifier is described by
wH = lower cutoff frequency or lower half-power point of amplifier.
Microelectronic Circuit Design, 3E
McGraw-Hill

3. High-pass Amplifier: Magnitude and Phase Response
High-pass filter symbol
Bandwidth (frequency range with constant amplification ) is infinite
Phase response is given by
Microelectronic Circuit Design, 3E
McGraw-Hill

4. Microelectronic Circuit Design, 3E
RC High-pass Filter
Problem: Find voltage transfer
function
Approach: Impedance of the where
capacitor is 1/sC, use voltage
division
Microelectronic Circuit Design, 3E
McGraw-Hill

5. Band-pass Amplifier: Description
Band-pass characteristic obtained by combining high-pass and low-pass characteristics.
Transfer function of a band-pass amplifier is given by
ac-coupled amplifier has a band-pass characteristic:
Capacitors added to circuit cause low frequency roll-off
Inherent frequency limitations of solid-state devices cause high-frequency roll-off.
Microelectronic Circuit Design, 3E
McGraw-Hill

6. Band-pass Amplifier: Magnitude and Phase Response
The frequency response shows a wide band of operation.
Mid-band range of frequencies given by
Transfer characteristic is
Microelectronic Circuit Design, 3E
McGraw-Hill

7. Band-pass Amplifier: Magnitude and Phase Response (cont.)
At both wH and wL, assuming wL<<wH,
Bandwidth = wH - wL.
The phase response is given by
Microelectronic Circuit Design, 3E
McGraw-Hill

8. Narrow-band or High-Q Band-pass Amplifiers
Gain maximum at center frequency wo and decreases rapidly by 3 dB at wH and wL.
Bandwidth defined as wH - wL, is a small fraction of wo with width determined by:
For high Q, poles will be complex and
Phase response is given by:
Band-pass filter symbol
Microelectronic Circuit Design, 3E
McGraw-Hill

9. Band-Rejection Amplifier or Notch Filter
Gain maximum at frequencies far from wo and exhibits a sharp null at wo.
To achieve sharp null, transfer function has a pair of zeros on jw axis at notch frequency wo , and poles are complex.
Phase response is given by:
Band-reject filter symbol
Microelectronic Circuit Design, 3E
McGraw-Hill

10. Microelectronic Circuit Design, 3E
All-pass Function
Uniform magnitude response at all frequencies.
Can be used to tailor phase characteristics of a signal
Transfer function is given by:
For positive Ao,
Microelectronic Circuit Design, 3E
McGraw-Hill

11. Complex Transfer Functions
Amplifier has 2 frequency ranges with constant gain. The mid-band region is always defined as region of highest gain and cutoff frequencies are defined in terms of midband gain.
Since wH  w4 and wL  w3,
Microelectronic Circuit Design, 3E
McGraw-Hill

12. Microelectronic Circuit Design, 3E
Bandwidth Shrinkage
If critical frequencies aren’t widely spaced, the poles and zeros interact and cutoff frequency determination becomes complicated.
Example : for which Av(0) = Ao
Upper cutoff frequency is defined by
Solving for wH yields wH = 0.644w1. The cutoff frequency of two-pole function is only 64% that of a single-pole function. This is known as bandwidth shrinkage.
Microelectronic Circuit Design, 3E
McGraw-Hill