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Interfacing Methods and Circuits

Interfacing Methods and Circuits

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The purpose of this chapter is to discuss the general issues associated with interfacing and to outline the more general interfacing circuits the engineer is likely to be exposed to. However, no general discussion can prepare one for all eventualities and it should be recognized that there are both exceptions and extensions to the methods discussed here. For example, an A/D is a simple - if not inexpensive - method of digitizing a signal for the purpose of interfacing with a microprocessor. However, this approach may not be necessary, or may be too expensive, in some cases. A case in point: Suppose that a Hall element is used to sense the teeth on a rotating gear. The signal from the Hall element is an AC voltage (more or less sinusoidal) and only the peaks are necessary to sense the gears. In this case a simple peak detector, followed perhaps by simple signal conditioning may be adequate. An A/D converter will not provide any additional benefit and is a much more complex and expensive solution. On the other hand, if a microprocessor is used and an A/D converter is available onboard, it may be acceptable to use it for this purpose in lieu of adding circuitry.

Chapter Contents:

  • 11.1 Introduction
  • 11.2 Amplifiers
  • 11.2.1 The Operational Amplifier
  • 11.2.1.1 Differential Voltage Gain
  • 11.2.1.2 Common-Mode Voltage Gain
  • 11.2.1.3 Bandwidth
  • 11.2.1.4 Slew Rate
  • 11.2.1.5 Input Impedance
  • 11.2.1.6 Output Impedance
  • 11.2.1.7 Temperature Drift and Noise
  • 11.2.1.8 Power Requirements
  • 11.2.2 Inverting and Noninverting Amplifiers
  • 11.2.2.1 The Inverting Amplifier
  • 11.2.2.2 The Noninverting Amplifier
  • 11.2.3 The Voltage Follower
  • 11.2.4 The Instrumentation Amplifier
  • 11.2.5 The Charge Amplifier
  • 11.2.6 The Integrator and the Differentiator
  • 11.2.7 The Current Amplifier
  • 11.2.8 The Comparator
  • 11.3 Power Amplifiers
  • 11.3.1 Linear Power Amplifiers
  • 11.3.2 PWM and PWM Amplifiers
  • 11.4 Digital Circuits
  • 11.5 A/D and D/A Converters
  • 11.5.1 A/D Conversion
  • 11.5.1.1 Threshold Digitization
  • 11.5.1.2 Threshold Voltage-to-Frequency Conversion
  • 11.5.1.3 True A/D Converters
  • 11.5.1.4 Dual-Slope A/D Converter
  • 11.5.1.5 Successive Approximation A/D
  • 11.5.2 D/A Conversion
  • 11.5.2.1 Resistive Ladder Network D/A Conversion
  • 11.5.2.2 PWM D/A Conversion
  • 11.5.2.3 Frequency to Voltage (F/V) D/A Conversion
  • 11.6 Bridge Circuits
  • 11.6.1 Sensitivity
  • 11.6.2 Bridge Output
  • 11.7 Data Transmission
  • 11.7.1 Four-Wire Transmission
  • 11.7.2 Two-Wire Transmission for Passive Sensors
  • 11.7.3 Two-Wire Transmission for Active Sensors
  • 11.7.4 Digital Data Transmission Protocols and Buses
  • 11.8 Excitation Methods and Circuits
  • 11.8.1 Linear Power Supplies
  • 11.8.2 Switching Power Supplies
  • 11.8.3 Current Sources
  • 11.8.4 Voltage References
  • 11.8.5 Oscillators
  • 11.8.5.1 Crystal Oscillators
  • 11.8.5.2 LC and RC Oscillators
  • 11.9 Noise and Interference
  • 11.9.1 Inherent Noise
  • 11.9.2 Interference
  • 11.10 Problems

Inspec keywords: sensors; oscillators; microprocessor chips; bridge circuits; amplifiers; digital-analogue conversion; analogue-digital conversion

Other keywords: square wave oscillators; A-D converter; Hall element; AC excitation sources; simple peak detector; DC power supplies; interfacing method; rotating gear; amplifiers; interfacing circuits; bridge circuits; microprocessor; sensors; signal conditioning; AC voltage; signal digitization; sinusoidal wave oscillators

Subjects: Amplifiers; A/D and D/A convertors; Microprocessors and microcomputers; Oscillators; Sensing devices and transducers

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