Tuesday, May 03, 2011

Low-Power, Unity-Gain Difference Amplifier Implements Low-Cost Current Source

In Difference Amplifier Forms Heart of Precision Current Source, published in Analog Dialogue in September 2009, the AD8276 unity-gain difference amplifier and AD8603 micropower op amp were used to implement a precision current source. This article shows how the circuit can be simplified for use in low-cost, low-current applications—achieving ±1.5% accuracy from –40°C to +85°C.


At 6:07 AM, Anonymous AndyB said...

If you use this design to apply constant current excitation to (say) a strain gauge bridge, be aware that the device mentioned has an output noise of 65nV per sqrt(Hz). The noise may ultimately restrict the bandwidth of signals that you may hope to measure on the gauge.

At 7:35 AM, Anonymous Anonymous said...

Yes. You are right. it’s a matter of if the noise cuts into the resolution of the measurement required. As you know, noise spectral density is integrated over frequency/BW of the system or measurement, right ~ [noise SD x sqrt(freq) ] to get your rms noise…

So as you increase the BW of the measurement, the rms noise and pk-pk noise also increases, and depending on the requirement, the noise might be too much and will start to affect the resolution of the system.
(The AD8476 is not exactly “low noise” but also the internal resistors contribute much of that noise).


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