period of the fundamental frequency to be rejected. The maximum conversion rate is slightly less than 1/(2T) conversions per second. While this limits the conversion rate to be too slow for high-speed data acquisition applications, it is appropriate for long-duration applications of slowly varying input signals Grounding and bypassing on d/A and A/D ICs D/A and a/d converter ICs require correct grounding and capacitive bypassing in order to operate according to performance specifications. The digital signals can severely impair analog signals. To combat the electro magnetic interference induced by the digital signals, the analog and digital grounds should be kept separate and should have only one common point on the circuit board. If possible, this common point should be the connection to the power supply. Bypass capacitors are required at the power connections to the IC, the reference signal inputs, and the analog ats to minimize noise that is induced by the digital sig lufacturer specifies the recommended bypass capacitor locations and values in the data sheet. The 1-uF tantalum capacitors are commonly recom- mended, with additional high-frequency power supply decoupling sometimes being recommended through the use of ceramic disc shunt capacitors. The manufacturers' recommendations should be followed to ensure proper per Selection Criteria for D/A and A/D Converter ICs Hundreds of D/A and A/D converter ICs are available, with prices ranging from a few dollars to several hundred dollars each. The selection of the appropriate type of converter is based on the application requirements of the system,the performance requirements, and cost. The following issues should be considered in order to select the appropriate converter. 1. What are the input and output requirements of the system? Specify all signal current and voltage ranges, logic levels, input and output impedances, digital codes, data rates, and data formats 2. What level of accuracy is required? Determine the resolution needed throughout the analog voltage range,the dynamic response, the degree of linearity, and the number of bits encoding. 3. What speed is required? Determine the maximum analog input frequency for sampling in an A/D system the number of bits for encoding each analog signal, and the rate of change of input digital codes in a D/A system. 4. What is the operating environment of the system? Obtain information on the temperature range and power supply to select a converter that is accurate over the operating range Final selection of D/A and A/D converter ICs should be made by consulting manufacturers to obtain their technical specifications of the devices. Major manufacturers of D/A and A/D converters include Analog Devices, Burr-Brown, DATEL, Maxim, National, Phillips Components, Precision Monolithics, Signetics, Sony, Texas Instruments, Ultra Analog, and Yamaha. Information on contacting these manufacturers and others can be iC Master catalog Defining Terms Companding: A process designed to minimize the transmission bit rate of a signal by compressing it prior to transmission and expanding it upon reception. It is a rudimentary " data compressiontechnique that Delta modulation: An A/D conversion process where the digital output code represents the change, or slope, of the analog input signal, rather than the absolute value of the analog input signal. A l indicates a rising slope of the input signal. AO indicates a falling slope of the input signal. The sampling rate is dependent on the derivative of the signal, since a rapidly changing signal would require a rapid sampling rate for Fixed reference D/A converter: The analog output is proportional to a fixed (nonvarying) reference signal. e 2000 by CRC Press LLC© 2000 by CRC Press LLC period of the fundamental frequency to be rejected. The maximum conversion rate is slightly less than 1/(2T) conversions per second. While this limits the conversion rate to be too slow for high-speed data acquisition applications, it is appropriate for long-duration applications of slowly varying input signals. Grounding and Bypassing on D/A and A/D ICs D/A and A/D converter ICs require correct grounding and capacitive bypassing in order to operate according to performance specifications. The digital signals can severely impair analog signals. To combat the electro￾magnetic interference induced by the digital signals, the analog and digital grounds should be kept separate and should have only one common point on the circuit board. If possible, this common point should be the connection to the power supply. Bypass capacitors are required at the power connections to the IC, the reference signal inputs, and the analog inputs to minimize noise that is induced by the digital signals. Each manufacturer specifies the recommended bypass capacitor locations and values in the data sheet. The 1-mF tantalum capacitors are commonly recom￾mended, with additional high-frequency power supply decoupling sometimes being recommended through the use of ceramic disc shunt capacitors. The manufacturers’ recommendations should be followed to ensure proper performance. Selection Criteria for D/A and A/D Converter ICs Hundreds of D/A and A/D converter ICs are available, with prices ranging from a few dollars to several hundred dollars each. The selection of the appropriate type of converter is based on the application requirements of the system, the performance requirements, and cost. The following issues should be considered in order to select the appropriate converter. 1. What are the input and output requirements of the system? Specify all signal current and voltage ranges, logic levels, input and output impedances, digital codes, data rates, and data formats. 2. What level of accuracy is required? Determine the resolution needed throughout the analog voltage range, the dynamic response, the degree of linearity, and the number of bits encoding. 3. What speed is required? Determine the maximum analog input frequency for sampling in an A/D system, the number of bits for encoding each analog signal, and the rate of change of input digital codes in a D/A system. 4. What is the operating environment of the system? Obtain information on the temperature range and power supply to select a converter that is accurate over the operating range. Final selection of D/A and A/D converter ICs should be made by consulting manufacturers to obtain their technical specifications of the devices. Major manufacturers of D/A and A/D converters include Analog Devices, Burr-Brown, DATEL, Maxim, National, Phillips Components, Precision Monolithics, Signetics, Sony, Texas Instruments, Ultra Analog, and Yamaha. Information on contacting these manufacturers and others can be found in an IC Master Catalog. Defining Terms Companding: A process designed to minimize the transmission bit rate of a signal by compressing it prior to transmission and expanding it upon reception. It is a rudimentary “data compression” technique that requires minimal processing. Delta modulation: An A/D conversion process where the digital output code represents the change, or slope, of the analog input signal, rather than the absolute value of the analog input signal. A 1 indicates a rising slope of the input signal. A 0 indicates a falling slope of the input signal. The sampling rate is dependent on the derivative of the signal, since a rapidly changing signal would require a rapid sampling rate for acceptable performance. Fixed reference D/A converter: The analog output is proportional to a fixed (nonvarying) reference signal