Analog Angle Article

Innovative topology lets low-power op amp defeat crossover distortion

Dallas, TX–Low-power, single-supply operational amplifiers (op amp) are critical to many signal-conditioning applications, but have one unattractive attribute: they have crossover error and changes in their common-mode voltage, which is a result of their two-stage input topology and midway-biased input stage. As a result, there are offset voltage shifts, and significant offset-voltage distortion and errors over the common-mode range.

The OPA369 from Texas Instruments uses a new topology which the vendor claims overcomes this problem and reduces the problem to nearly zero, and thus yields a total error allocation for the four major contributing factors (AOL , PSRR, CMRR, and VOS ) that is far lower than competitive units. In addition, this op amp has quiescent current of 1 μA, and operates down to 1.8 V. Offset voltage over the entire rail-to-rail input range is 750 μV, with CMRR of at least 100 dB.

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Gain bandwidth is 12 kHz at 1 μA, and input bas current is 50 pA maximum. Other key specifications include voltage offset drift of 1.75 μV/°C, PSRR of 94 dB, noise of 120 nV/rt-Hz, and 1/f noise of 3.6 μVp-p (from 0.1 to 10 Hz).

Housed in a 5-lead SC-70 package, the OPA369 single op amp is $0.80 in 1000-piece lots. A dual version, the OPA2369, is available in SOT23 and MSOP packages, and is $1.20.

For more information, go to–by Bill Schweber

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