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, analog to digital conversion 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 analog to digital converter (A/D or ADC) 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
• 11.5.1.6 Flash analog-to-digital converter
• 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 Power harvesting
• 11.9.1 Solar power harvesting
• 11.9.2 Thermal gradient power harvesting
• 11.9.3 Magnetic induction and RF power harvesting
• 11.9.4 Power harvesting from vibrations
• 11.10 Noise and interference
• 11.10.1 Inherent noise
• 11.10.2 Interference
• 11.11 Problems

Inspec keywords: Hall effect transducers; signal conditioning circuits; peak detectors; analogue-digital conversion; gears; microprocessor chips

Other keywords: ADC; peak detector; rotating gear; signal conditioning; interfacing circuits; A/D conversion; microprocessor; analog to digital conversion; Hall element

Subjects: Signal processing and conditioning equipment and techniques; Bulk effect devices; Microprocessors and microcomputers; Sensing devices and transducers; A/D and D/A convertors; Modulators, demodulators, discriminators and mixers