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While digital potentiometers can make excellent digitally controlled voltage dividers in applications in which 8-bit resolution is acceptable, this circuit shows how to use a CMOS DAC as a voltage divider in applications requiring higher resolution.
The Design Idea begins:
"Millions of CMOS R2R (resistor/two-resistor)-ladder DACs have found use in attenuator applications in which an external op amp acting as a current-to-voltage converter forces one current-output terminal to a virtual ground. The reference input to the DAC can be ac or dc as long as the op amp can produce the desired output voltage. A phase inversion is normal between input and output, so the circuit requires dual power supplies."
"Figure 1 shows a way to rewire this simple circuit to avoid the phase inversion and to operate with a single supply. In this configuration, the DAC acts as a digitally programmable resistor, and the DAC's code changes the effective resistance between the input voltage and the IOUT1 output-current terminal of the DAC."
Read the full Circuit Design Idea
It is courtesy of John Wynne and Liam Riordan, of Analog Devices in Limerick, Ireland (edited by Martin Rowe and Fran Granville of EDN).
View all the Design Ideas on Electronics Weekly
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