1	Chapter 31 Applications of Op-Amps
2	Comparators Op-amp as a Comparator No negative feedback Output saturates with very small + or – input
3	Comparators Comparator Non-linear device v_out has two discrete values, ±V_SAT v_out = +V_SAT if + input is greater than – input v_out = –V_SAT if – input is greater than + input
4	Comparators A comparator circuit: Sine wave in, square wave out
5	Comparators Input sine wave Output square wave V_out = ±V_SAT +V_SAT (determined by V_CC) when sinusoid is + –V_SAT (determined by V_EE) when sinusoid is –
6	Comparators Compare input waveform to reference Reference can be ground or dc source Can compare two waveforms Specialized comparator IC’s also available Detects when waveform reaches given level
7	Comparators Zero-Crossing Detector
8	Voltage Summing Amplifier Circuit
9	Voltage Summing Amplifier Inverse sum
10	Voltage Summing Amplifier Multiplies each input by
11	Integrators and Differentiators In general Using resistors and capacitors Integrators Differentiators
12	Integrators and Differentiators Voltage across capacitor Current through capacitor
13	Integrators and Differentiators Op-amp Integrator
14	Integrators and Differentiators Op-amp differentiator Circuit inherently unstable
15	Integrators and Differentiators Stable op-amp differentiator
16	Instrumentation Amplifiers Op-amp in differential amplifier configuration Noise suppression High CMRR Reasonable gain IC instrumentation amps
17	Instrumentation Amplifiers An op-amp instrumentation amp circuit
18	Instrumentation Amplifiers Measurement of very small voltages Transducer Converts a physical change into an electrical change
19	Instrumentation Amplifiers Strain gage Converts force into ∆R ∆R is milliohms Use bridge circuit
20	Instrumentation Amplifiers Strain gage example Thin metal foil (resistor) on plastic backing Glued to metal bar Bar subjected to tension and compression
21	Instrumentation Amplifiers Strain gage example Tension Resistance of strain gage is R + ∆R Compression Resistance of strain gage is R – ∆R
22	Active Filters Basic filter types Passive elements, gain < 1 Low-pass High-pass Bandpass Band reject
23	Active Filters With op-amps/active filters Gain can be ≥ 1 Filter response closer to ideal
24	Active Filters Low-pass (R_F = R₁) Add resistor for gain > 1
25	Active Filters High-pass (R_F = R₁) Add resistor for gain > 1
26	Active Filters dc gain Easily achieved Not used much due to gain-bandwidth product Example GBWP = 10⁶, Gain = 10 Cutoff for filter (HP or LP) only 10⁵
27	Active Filters Bandpass Wideband Cascade HP and LP active filters LP must have higher cutoff frequency HP and LP cutoff frequencies far apart Narrowband Can use single op-amp
28	Active Filters Narrowband BP circuit
29	Active Filters Active notch filter Cascade narrowband BP filter Adder circuit Result is 1 – (frequency response of BP filter) Frequency at resonant frequency of BP filter will be eliminated
30	Voltage Regulation Voltage regulator Constant voltage to load Specified current range Specified input voltage range Zener diode regulator Inefficient Dissipates power
31	Voltage Regulation Types of regulators Fixed voltage regulator Variable voltage regulator Switching regulator Specialized IC regulators For different voltages, e.g. +5 V, –5 V, +12 V, –12 V, +15 V, –15 V, etc.
32	Voltage Regulation Line Regulation Small output change with change in input
33	Voltage Regulation Load regulation Small output voltage change with smaller R_L V_NL = no-load voltage (open-circuit load) V_FL = full-load voltage (specified by manufacturer)
34	Voltage Regulation Circuit to increase efficiency of Zener regulator with an op-amp
35	Voltage Regulation Three-terminal IC regulators 7800 series, positive voltage 7900 series, negative voltage
36	Voltage Regulation 5 V output, 7805 12 V output, 7812 –5 V output, 7905 –12 V output, 7912
37	Voltage Regulation Ripple Greatly reduced by IC regulator V_r(in) = input ripple voltage V_r(out) = output ripple voltage