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Interfacing Devices Chapter 2 Objectives • Identify the schematic diagrams, describe the operations, and calculate the outputs of the comparator, inverting, summing, noninverting, and difference operational amplifiers (op amps) • Identify the schematic diagrams of the integrator and differentiator op amps and draw the output waveforms they produce when various input signals are applied Objectives (cont’d.) • Given applied input signals, indicate the resulting output of the digital comparator device • Describe the wave-shaping capability and operating characteristics of a Schmitt trigger • Determine how optoelectronic devices are switched and explain the isolation function they perform Objectives (cont’d.) • Explain the operation of analog-to-digital and digital-to-analog converters, determine their resolution, and make the proper wiring connections to their integrated circuit packages • Assemble monostable and astable multivibrators using a 555 monolithic integrated circuit and use calculations to determine their output Fundamental Operational Amplifiers • Op amps – uA741: one of the most popular • Operational amplifier comparator • Inverting operational amplifier – Control gain using feedback Fundamental Operational Amplifiers • Summing amplifier – Two or more inputs are tied together and then applied to an input lead of an op amp FIGURE 2-5 Inverting summing amplifier Fundamental Operational Amplifiers • Noninverting amplifier – Equation used to determine the gain: – Output voltage: • Difference operational amplifier – Finds the algebraic difference between two input voltages Signal Processors • Devices that change or modify signals applied to inputs • Integrator operational amplifier – Continuously increases its gain over a period of time • Differentiator operational amplifier – Produces an output proportional to the rate of change of the input signal Signal Processors (cont’d.) • Wave-shaping Schmitt trigger – Device that produces rectangular wave signals – Operation: three time periods FIGURE 2-10b Schmitt trigger Comparator Devices • Function: produce an output error signal that is determined by the difference between the two inputs • Magnitude comparator – Compare two binary numbers – 4-bit magnitude comparator • Connect several to compare larger numbers Optoelectronic Interface Devices • Pass electrical signals from one element to another by means of light energy and semiconductors – Light source: usually a semiconductor light emitting diode (LED) • Photodiode – PN-junction device that operates in the reverse-bias mode Optoelectronic Interface Devices (cont’d.) • Phototransistor – Depends on a light source for its operation • Photo SCR – Light-activated SCR, or LASCR – Usually activated by light rather than a gate voltage that draws gate current Optoelectronic Interface Devices (cont’d.) • Photo triac – Bidirectional device designed to switch AC signals and pass current in both directions • Optocoupler – Package does not allow light to enter • Optoisolator – No electrical connection between the emitter and the detector Digital-to-Analog Converters • Convert digital signals representing binary numbers into proportional analog voltages • Resolution – Number of equal divisions into which a DAC divides the reference voltage • Integrated-circuit digital-to-analog converter – Example: 8-bit DAC0808 Analog-to-Digital Converters • Converts analog input voltages into proportional digital number • Successive-approximation register (SAR) – Circuit used to operate at high speeds • Integrated-circuit analog-to-digital converter – Example: ADC0804 Timing Devices • Produce rectangular signals referred to as square-wave signals • Monostable multivibrators – Produce single pulse signals – Example: 555 monostable multivibrator • Astable multivibrators – Produce continuous pulse signals – Example: 555 astable multivibrator