High Precision Digital-to-Analog Conversion Using the 16-Bit AD5542/AD5541 Voltage Output DAC, ADR421 Reference, and AD8628 Auto-Zero Op Amp (cn0079)
This circuit provides precision data conversion using the AD5542 voltage output DAC together with the ADR421BRZ voltage reference and the AD8628 auto-zero op amp as the reference buffer. The AD8628 reference buffer provide benefits previously found only in expensive auto-zeroing or chopper-stabilized amplifiers. Using Analog Devices, Inc., circuit topology, these zero-drift amplifiers combine low cost with high accuracy and low noise. No external capacitor is required, and the digital switching noise associated with most chopper-stabilized amplifiers is greatly reduced, thereby making this the optimum choice for reference buffering.
This circuit provides precision, low power, voltage output, digital-to-analog conversion. The AD5542 can be operated in either the buffered or unbuffered mode. The application and its requirements on settling time, input impedance, noise, etc., determine which mode of operation is best. The selection of the output buffer amplifier can be tailored to suit either dc precision or fast settling time. Where the DAC is required to drive a load less than 60 kΩ, an output buffer will be required. The output impedance of the DAC is constant and code independent, but to minimize gain errors the input impedance of the output amplifier should be as high as possible. The output amplifier should also have a 3 dB bandwidth of 1 MHz or greater. The output amplifier adds another time constant to the system, thereby increasing the settling time of the final output.
A higher 3 dB amplifier bandwidth results in a faster effective settling time of the combined DAC and amplifier. All devices in the circuit can be powered from a single +5 V supply. The input voltage range of the ADR421 reference is 4.5 V to 18 V.
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