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

2. Amplifier Biasing for Linear Operation
VI = dc value of vI,
vi = time-varying component
For linear amplification - vI must be biased in desired region of output characteristic by VI.
If slope of output characteristic is positive, input and output are in phase (amplifier is non-inverting).
If slope of output characteristic is negative, input and output signals are 1800 out of phase (amplifier is inverting).
Microelectronic Circuit Design, 3E
McGraw-Hill

3. Amplifier Biasing for Linear Operation (cont.)
Voltage gain depends on the choice of bias point.
Eg: if amplifier is biased at VI = 0.5 V, voltage gain will be +40 for input signals satisfying
If input exceeds this value, output is distorted due to change in amplifier slope.
Microelectronic Circuit Design, 3E
McGraw-Hill

4. Amplifier Biasing for Linear Operation (cont.)
Output signals for 1 kHz sinusoidal input signal of amplitude 50 mV biased at VI = 0.3 V and VI = 0.5V:
For VI = 0.3V:
Gain is 20; output varies about dc level of 4 V.
For VI = 0.5V:
Gain is 40; output varies about dc level of 10 V.
Microelectronic Circuit Design, 3E
McGraw-Hill

5. Distortion in Amplifiers
Different gains for positive and negative values of input cause distortion in output.
Total Harmonic Distortion (THD) is a measure of signal distortion that compares undesired harmonic content of a signal to the desired component.
Microelectronic Circuit Design, 3E
McGraw-Hill

6. Total Harmonic Distortiondc
desired output
2nd harmonic distortion
3rd harmonic distortion
Numerator = rms amplitude of distortion terms,
Denominator = desired component
Microelectronic Circuit Design, 3E
McGraw-Hill

7. Amplifier Transfer Functions
Av(s) = Frequency-dependent voltage gain
Vo(s) and Vs(s) = Laplace Transforms of input and output voltages of amplifier,
(In factorized form)
(-z1, -z2,…-zm) = zeros (frequencies for which transfer function is zero)
(-p1, -p2,…-pm) = poles (frequencies for which transfer function is infinite)
(In polar form)
Bode plots display magnitude of the transfer function in dB and the phase in degrees (or radians) on a logarithmic frequency scale..
Microelectronic Circuit Design, 3E
McGraw-Hill

8. Low-Pass Amplifier: Description
Amplifies signals over a range of frequencies including dc.
Most operational amplifiers are designed as low pass amplifiers.
Simplest (single-pole) low-pass amplifier is described by
Ao = low-frequency gain or mid-band gain
wH = upper cutoff frequency or upper half-power point of amplifier.
Microelectronic Circuit Design, 3E
McGraw-Hill

9. Low-pass Amplifier: Magnitude Response
Low-pass filter symbol
Gain is unity (0 dB) at w = AowH = wT called gain-bandwidth product
Bandwidth (frequency range with constant amplification ) = wH (rad/s)
Microelectronic Circuit Design, 3E
McGraw-Hill

10. Low-pass Amplifier: Phase Response
If Ao positive: phase angle = 00
If Ao negative: phase angle = 1800
At wC: phase = 450
One decade below wC: phase = 5.70
One decade above wC: phase = 84.30
Two decades below wC: phase = 00
Two decades above wC: phase = 900
Microelectronic Circuit Design, 3E
McGraw-Hill

11. Microelectronic Circuit Design, 3E
RC Low-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