Instrumentation Amplifier Chips

Instrumentation amplifier chips are precision amplifier circuits with both high-impedance differential inputs and high common-mode rejection. Instrumentation amplifier chips or instrument amps are a type of operational amplifier that, because of high input impedance and high common-mode rejection, are used for very accurate, low-noise measurements. The differential gain of an instrumentation amplifier chip can be adjusted by changing the value of a single resistor.

Specifications for instrumentation amplifier chips include input common mode voltage range to negative rail, rail to rail (input or output), gain, minimum stable closed loop gain, maximum supply current, maximum voltage offset, typical common mode rejection ratio at DC, typical power supply rejection ratio at DC, maximum input bias current, typical unity gain bandwidth, typical slew rate, input voltage noise, input current noise, frequency at which noise is specified, and supply voltage. Other specifications for instrumentation amplifier chips may be considered. The resistors for an instrument amp are often in the kO range. Resistors below 1 kO can cause excessive current flow and possible damage to the amplifier chip. Resistors above 1 MO can cause excessive thermal noise and bias currents in the amplifier circuit. Features for instrumentation amplifier chips include radiation hardening and low-power shutdown of the integrated amplifier. When manufactured as part of an integrated circuit chip, instrumentation amplifier chips are available in standard packaging.

Instrumentation amplifier chips that meet U.S. military specifications (MIL-SPEC) are manufactured according to standards described in MIL-STD-750 (Test Method Standard for Semiconductor Devices) and MIL-HDBK-6100 (Military Handbook, List of Case Outlines and Dimensions for Discrete Semiconductor Devices). Like other components made of semiconductor material, instrumentation amplifier chips that are marketed in European Union (EU) nations should be manufactured in compliance with the Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE) Directives. RoHS requires all manufacturers of electronic and electrical equipment sold in Europe to demonstrate that their products contain only minimal levels of the following hazardous substances: lead, mercury, cadmium, hexavalent chromium, and polybrominated biphenyl and polybrominated diphenyl ether. RoHS will become effective on July 1, 2006. By definition, lead-free devices contain less than 1000 ppm lead by weight.

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