Cancel Multiplexed DAC's Output Error, And Add A Sign Bit

June 10, 2002
In some applications, like dataloggers, it's desirable to have many multiplexed analog outputs. As only a single output is active at once, a voltage-output digital-to-analog converter (DAC) and an analog multiplexer can do this. You can use this kind...

In some applications, like dataloggers, it's desirable to have many multiplexed analog outputs. As only a single output is active at once, a voltage-output digital-to-analog converter (DAC) and an analog multiplexer can do this. You can use this kind of signal to excite bridges. A bipolar output may also be needed, but you don't want to give up a bit of resolution.

To address the first problem, designers usually implement a multiplexer (Fig. 1a). But this arrangement has a serious drawback: The output accuracy could be greatly reduced due to the multiplexer's internal impedance, RON. Figure 1b shows the added error, E, of AOx, the final output.

Low-internal-impedance multiplexers (RON less than 4Ω) are commercially offered at medium prices (about $0.95). Compare this to the HCT4052's RON (under 280 Ω) that runs $0.10. Alternatively, you can use four op amps to buffer each output.

The circuit of Figure 2 employs an original, low-cost technique to take advantage of the HCT4052's low price. The multiplexer's internal resistance is inserted in the feedback loop of an op amp, and the error, E, is almost cancelled. To add a sign bit, the versatile circuit employs another multiplexer and a unity-gain differential amplifier, which is fed with the DAC's output, or its inverse. This arrangement can be easily modified to add an arbitrary number of outputs by simply changing U3.

Sponsored Recommendations

Highly Integrated 20A Digital Power Module for High Current Applications

March 20, 2024
Renesas latest power module delivers the highest efficiency (up to 94% peak) and fast time-to-market solution in an extremely small footprint. The RRM12120 is ideal for space...

Empowering Innovation: Your Power Partner for Tomorrow's Challenges

March 20, 2024
Discover how innovation, quality, and reliability are embedded into every aspect of Renesas' power products.

Article: Meeting the challenges of power conversion in e-bikes

March 18, 2024
Managing electrical noise in a compact and lightweight vehicle is a perpetual obstacle

Power modules provide high-efficiency conversion between 400V and 800V systems for electric vehicles

March 18, 2024
Porsche, Hyundai and GMC all are converting 400 – 800V today in very different ways. Learn more about how power modules stack up to these discrete designs.

Comments

To join the conversation, and become an exclusive member of Electronic Design, create an account today!