Analog Angle Article

Innovative op amp architecture continues quest for zero offset voltage

Chandler, Ariz. –In the quest for the “perfect” op amp–in this case, meaning zero offset voltage, Vos –several 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, which the vendor claims is the first op amp to use this technique.

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

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The 2.5 to 5.5 V 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 μV after calibration, with maximum quiescent current of 9 mA, maximum input bias current of 0.006 nA. Operating temperature range is -40 to +125°C.

Tools and support : These op amps are 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.

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

For more information , contact Microchip Technology Inc,

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