Flash A/D: The fastest A/D conversion process available to date, also referred to as parallel A/D conversion The analog signal is simultaneously evaluated by 2n-1 comparators to produce an n-bit digital code in one step. Because of the large number of comparators required, the circuitry for flash A/D converters can be very expensive. This technique is commonly used in digital video systems Integrating A/D: The analog input signal is integrated over time to produce a digital signal that represents the area under the curve, or the integral Multiplying D/A: A D/A conversion process where the output signal is the product of a digital code multiplied times an analog input reference signal. This allows the analog reference signal to be scaled by a digital code. yquist A/D converters: A/D converters that sample analog signals that have a maximum frequency that is less than the Nyquist frequency. The Nyquist frequency is defined as one-half of the sampling frequency If a signal has frequencies above the Nyquist frequency, a distortion called aliasing occurs. To prevent aliasing, an antialiasing filter with a flat passband and very sharp roll-off is required. Oversampling converters: A/D converters that sample frequencies at a rate much higher than the Nyquist frequency. Typical oversampling rates are 32 and 64 times the sampling rate that would be required with the Nyquist converters Pulse code modulation(PCM): An A/D conversion process requiring three steps: the analog signal is sa quantized, and encoded into a fixed length digital code. This technique is used in many digital voice and audio systems. The reverse process reconstructs an analog signal from the PCM code. The operation is very similar to other A/D techniques, but specific PCM circuits are optimized for the particular voice or dio applicatio Sigma-delta A/D conversion: An oversampling A/D conversion process where the analog signal is sampled at rates much higher(typically 64 times)than the sampling rates that would be required with a Nyquist converter. Sigma-delta modulators integrate the analog signal before performing the delta modulation The integral of the analog signal is encoded rather than the change in the analog signal, as is the case for traditional delta modulation. A digital sample rate reduction filter(also called a digital decimation lter)is used to provide an output sampling rate at twice the Nyquist frequency of the signal. The overall result of oversampling and digital sample rate reduction is greater resolution and less distortion compared to a Nyquist converter process Successive approximation: An A/D conversion process that systematically evaluates the analog signal in n steps to produce an n-bit digital code. The analog signal is successively compared to determine the digital code, beginning with the determination of the most significant bit of the code Related Topic 15.1 Coding, Transmission, and Storage References Analog Devices, Analog Devices Data Conversion Products Data Book, Norwood, Mass. Analog Devices, Inc. Burr-Brown, Burr-Brown Integrated Circuits Data Book, Tucson, Ariz: Burr-Brown, 1989 DATEL, DATEL Data Conversion Catalog, Mansfield, Mass.: DATEL, Inc., 1988 w. Drachler, and M. Bill,"New high-speed, low-power data-acquistion ICs, Analog Dialogue, vol. 29, no. 2, pp. 3-6, Norwood, Mass. Analog Devices, Inc., 1995 S. Garrod and R. Borns, Digital Logic: Analysis, Application and Design, Philadelphia, Pa. Saunders College Publishing, 1991, Chap. 16 J M. Jacob, Industrial Control Electronics, Englewood Cliffs, N J. Prentice-Hall, 1989, Chap. 6 B Keiser and E Strange, Digital Telaphony and Network Integration, 2nd ed, New York: Van Nostrand Reinhold, Motorola. Motorola telecommunications data book phoenix, Ariz. Motorola Inc. 1989. National Semiconductor, National Semiconductor Data Acquisition Linear Devices Data Book, Santa Clara, Calif: National Semiconductor Corp. 1989 c2000 by CRC Press LLC© 2000 by CRC Press LLC Flash A/D: The fastest A/D conversion process available to date, also referred to as parallel A/D conversion. The analog signal is simultaneously evaluated by 2n – 1 comparators to produce an n-bit digital code in one step. Because of the large number of comparators required, the circuitry for flash A/D converters can be very expensive. This technique is commonly used in digital video systems. Integrating A/D: The analog input signal is integrated over time to produce a digital signal that represents the area under the curve, or the integral. Multiplying D/A: A D/A conversion process where the output signal is the product of a digital code multiplied times an analog input reference signal. This allows the analog reference signal to be scaled by a digital code. Nyquist A/D converters: A/D converters that sample analog signals that have a maximum frequency that is less than the Nyquist frequency. The Nyquist frequency is defined as one-half of the sampling frequency. If a signal has frequencies above the Nyquist frequency, a distortion called aliasing occurs. To prevent aliasing, an antialiasing filter with a flat passband and very sharp roll-off is required. Oversampling converters: A/D converters that sample frequencies at a rate much higher than the Nyquist frequency. Typical oversampling rates are 32 and 64 times the sampling rate that would be required with the Nyquist converters. Pulse code modulation (PCM): An A/D conversion process requiring three steps: the analog signal is sampled, quantized, and encoded into a fixed length digital code. This technique is used in many digital voice and audio systems. The reverse process reconstructs an analog signal from the PCM code. The operation is very similar to other A/D techniques, but specific PCM circuits are optimized for the particular voice or audio application. Sigma-delta A/D conversion: An oversampling A/D conversion process where the analog signal is sampled at rates much higher (typically 64 times) than the sampling rates that would be required with a Nyquist converter. Sigma-delta modulators integrate the analog signal before performing the delta modulation. The integral of the analog signal is encoded rather than the change in the analog signal, as is the case for traditional delta modulation. A digital sample rate reduction filter (also called a digital decimation filter) is used to provide an output sampling rate at twice the Nyquist frequency of the signal. The overall result of oversampling and digital sample rate reduction is greater resolution and less distortion compared to a Nyquist converter process. Successive approximation: An A/D conversion process that systematically evaluates the analog signal in n steps to produce an n-bit digital code. The analog signal is successively compared to determine the digital code, beginning with the determination of the most significant bit of the code. Related Topic 15.1 Coding, Transmission, and Storage References Analog Devices, Analog Devices Data Conversion Products Data Book, Norwood, Mass.: Analog Devices, Inc., 1989. Burr–Brown, Burr-Brown Integrated Circuits Data Book, Tucson, Ariz.: Burr-Brown, 1989. DATEL, DATEL Data Conversion Catalog, Mansfield, Mass.: DATEL, Inc., 1988. W. Drachler, and M. Bill, “New high-speed, low-power data-acquistion ICs,” Analog Dialogue, vol. 29, no. 2, pp. 3–6, Norwood, Mass.: Analog Devices, Inc., 1995. S. Garrod and R. Borns, Digital Logic: Analysis, Application and Design, Philadelphia, Pa.: Saunders College Publishing, 1991, Chap. 16. J.M. Jacob, Industrial Control Electronics, Englewood Cliffs, N.J.: Prentice–Hall, 1989, Chap. 6. B. Keiser and E. Strange, Digital Telaphony and Network Integration, 2nd ed., New York: Van Nostrand Reinhold, 1995. Motorola, Motorola Telecommunications Data Book, Phoenix, Ariz.: Motorola, Inc., 1989. National Semiconductor, National Semiconductor Data Acquisition Linear Devices Data Book, Santa Clara, Calif.: National Semiconductor Corp., 1989