Electronic PRINCIPLES

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1 MALVINO & BATES Electronic PRINCIPLES SEVENTH EDITION

2 Chapter 22 Nonlinear Op-Amp Circuits

3 Topics Covered in Chapter 22 Comparators with zero reference Comparators with non-zero references Comparators with hysteresis Window comparator The integrator Waveform conversion

4 Topics Covered in Chapter 22 (Continued) Waveform generation Another triangular generator Active diode circuits The differentiator Class D amplifier

5 Comparators with zero reference Called zero-crossing detectors Diode clamps used to protect comparators against large inputs Usually interface their outputs with digital circuits

6 Inverting comparator A VOL 100,000 +V CC Diode clamps for protection -V EE +V sat -V sat

7 The trip point of a zero-crossing detector should be near zero volts Inverting comparator with input bias compensation +V CC R B R B -V EE

8 Bounded output zero-crossing detector +V CC -V EE +V Z V Z - 07

9 Comparators with non-zero references Sometimes called limit detectors Op amps may be used IC comparators are optimized by removing the internal compensating capacitor which increases switching speed

10 Non-inverting threshold detector +V CC R 2 R 2 V ref = ( V EE ) R 1 +R 2 R 1 -V EE V ref +V sat -V sat

11 IC comparators Op amps have speed limitations due to the internal compensation capacitor Comparator ICs are optimized for nonlinear operation so the capacitor is not needed Comparator ICs often have opencollector outputs to make interfacing more flexible

12 Using a pullup resistor with an open-collector output stage +V pullup resistor IC comparator When the transistor is off, the resistor pulls up to +V

13 Comparators with hysteresis Noise is any unwanted signal not related to the input Noise can cause false triggering Positive feedback creates hysteresis Hysteresis prevents false triggers and speeds up switching

14 The Schmitt trigger uses positive feedback +V CC B = R 1 R 1 +R 2 R 1 -V EE UTP = BV sat LTP = -BV sat UTP LTP R 2 H = 2BV sat +V sat -V sat

15 +V sat -V sat Comparing a zero-crossing detector to a Schmitt trigger when both have noisy input signals UTP LTP +V sat -V sat

16 Window comparator Called a double-ended limit detector Detects when the input voltage is between two limits Uses two comparators with two different trip points

17 Window comparator operation LTP +V CC +V sat D 1 -V EE LTP HTP +V CC HTP D 2 R L Output is low when input is in window -V EE

18 Integrator Useful for converting rectangular pulses into linear ramps Earliest part of exponential charge is used Output ramps are almost perfect Used to create time bases for oscilloscopes

19 Integrator circuit 10R 0 T R C 0 -T V = v RC in V

20 Waveform conversion A Schmitt trigger can be used to convert a sine wave to a rectangular wave An integrator can convert a square wave to a triangular wave The duty cycle of a limit detector can be controlled with an adjuster resistor

21 +V P Rectangular to triangular converter R 10R C -V P (pp) = V P 2fRC

22 Triangle to pulse converter R 2 V ref R 1 +V CC V ref = R 2 R 1 +R 2 V CC

23 Waveform generation Oscillators require no external input and still generate an output signal Oscillators work because of positive feedback A relaxation oscillator uses a charging capacitor A triangular waveform is produced by cascading a relaxation oscillator and an integrator

24 Relaxation oscillator UTP v C R 1 LTP C R R 2 T = 2RCln 1+B 1-B

25 Triangular waveform generator R 5 C 2 C 1 R 3 R 4 R 2 R 1

26 Another triangular waveform generator R 2 R 4 R 1 UTP = R 3 R 1 R 2 V sat C Schmitt trigger and cascaded integrator R 2 H = 2UTP V out(pp) = H f = 4R 1 R 3 C

27 Active half-wave rectifier R L V K(CL) = V K A VOL An op amp with negative feedback allows the rectification of signals with amplitudes less than the diode knee voltage

28 Active peak detector with reset R L C > 10T C R L Reset

29 Active positive clamper 0 R L An op amp with negative feedback allows the clamping of signals with amplitudes less than the diode knee voltage 0

30 Differentiator When a square wave drives an RC differentiator, the output is a series of narrow positive and negative voltage spikes Using an op amp will improve the differentiator and provide a low output impedance

31 Differentiator circuit and operation R 001R to 01R C

32 Class D amplifier Uses output transistors as switches These transistors are alternately driven into saturation and cutoff by the output of a comparator Provides very high circuit efficiencies Popular in portable equipment

Chapter 16: Oscillators

Chapter 16: Oscillators 16.1: The Oscillator Oscillators are widely used in most communications systems as well as in digital systems, including computers, to generate required frequencies and timing signals.