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  • MCP6N16 Zero-Drift Instrumentation Amplifier

  • Created: Jul 18, 2016

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An instrumentation amplifier is a differential operational amplifier circuit that provides high input impedances with ease of gain adjustment through variation of the gain resistor. This project features MCP6N16 zero-drift instrumentation amplifier with enable pin (EN) and three minimum gain options (GMIN). The device can be operated over a supply range of +1.8V to +5.5V (VDUT), which is low enough to support many portable applications. In this design, all devices are fully specified from -40°C to +125°C. Each part has EMI filters at the input pins, for good EMI rejection (EMIRR).

This reference design is a MCP6N16 evaluation board, which contains a sensor connector, differential input filtering, two jumper selectable gain settings and output filtering, in addition to an external voltage reference circuit to allow for an adjustable output common-mode level shifting. The sensor connector, J5, is a 6-pin screw terminal configured to accommodate a variety of sensors. Bridge-type sensors can have their excitation voltage connected to either the VDUT supply of the evaluation board or to an external power supply. In addition, the connector provides sense line connections. The evaluation board is populated with the MCP6N16-100, which is designed to be operated with a gain of +100V/V and higher. The power source in this design is separated into two segments: one labeled VDUT and one VS+. The VDUT supply line mainly powers the MCP6N16 instrumentation amplifier. It is also connected to be the supply rail for any attached bridge sensor (VB+, VB-). The VS+ supply powers the precision voltage reference MCP1525, and the zero-drift op-amp MCP6V11.

This board also includes external reference voltage to the MCP6N16, which can level shift the output signal. The MCP1525 (U2) is a precision, low-power voltage reference with an output voltage of +2.5V. Resistor R23 is a 25-turn potentiometer that is used to provide an adjustment range of +0.025V to +3.0V at the output of the reference buffer U4. The buffer amplifier uses the MCP6V11, a zero-drift micro-power operational amplifier that is configured for a gain of +1.2V/V. To minimize noise the bandwidth of this amplifier stage is limited to about 8Hz using capacitor C15, which is placed in parallel with the feedback resistor.



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