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Op amp architecture aims for zero offset voltage

Posted: 20 May 2009 ?? ?Print Version ?Bookmark and Share

Keywords:operational amplifier? op amp? voltage zero offset?

In the quest for the "perfect" operational amplifierwith zero offset voltage, VOSseveral techniques are in use, including design topology and technique; process improvement; test, active, on-chip trim; external calibration; internal calibration with EPROM-based calibration; and others. The latest entry is embedded in the MCP65X series of op amps (MCP651/2/5) from Microchip Technology Inc., which uses on-chip, one-shot digital calibration to correct the input offset voltage.

With typical gain bandwidth product (GBW) of 50MHz, the op amps have output drive current of 95mA, suitable for relatively large loads, as well as rail-to-rail outputs. Their internal design is similar to a successive-approximation register (SAR) ADC, with a comparator, reference, SAR control logic, and DAC to correct the offset voltage.

The 2.5V to 5.5V op amps automatically invoke the calibration scheme on power-up, and some versions can also be "instructed" to do so during operation via a reset-pin setting. Maximum initial offset voltage is 200?V after calibration, with maximum quiescent current of 9mA, maximum input bias current of 0.006nA. Operating temperature range is -40C to +125C.

The series is supported by Microchip's free FilterLab Analog Filtering Software Tool and their Mindi Online Simulator Tool, which provides schematics, circuits with component values, and filter frequency response.

Depending on specific device, the op amps are packaged in 8-pin SOIC, 3mm x 3mm DFN, and 10-lead MSOP packages. Pricing begins at $1.21 in 10K quantities.

- Bill Schweber
Planet Analog





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