Chapter 10 Analog Systems

1. Chapter 10Analog 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 • Bandwidth(frequency range with constant amplification ) is infinite • Phase response is given by High-pass filter symbol Microelectronic Circuit Design, 3E McGraw-Hill

4. 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 wHand wL, assumingwL<<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 wHand wL. • Bandwidth defined aswH - wL, is a small fraction ofwowith 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. 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. 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