a FEATURES User Programmed Gains of 1 to 10,000 Low Gain Error: 0.02% max Low Gain TC: 5 ppm/؇C max Low Nonlinearity: 0.001% max Low Offset Voltage: 25 V Low Noise 4 nV/√Hz (at 1 kHz) RTI Gain Bandwidth Product: 25 MHz 16-Pin Ceramic or Plastic DIP Package, 20-Pin LCC Package Standard Military Drawing Available MlL-Standard Parts Available Low Cost
Programmable Gain Instrumentation Amplifier AD625 FUNCTIONAL BLOCK DIAGRAM
The AD625 is a precision instrumentation amplifier specifically designed to fulfill two major areas of application: 1) Circuits requiring nonstandard gains (i.e., gains not easily achievable with devices such as the AD524 and AD624). 2) Circuits requiring a low cost, precision software programmable gain amplifier.
1. The AD625 affords up to 16-bit precision for user selected fixed gains from 1 to 10,000. Any gain in this range can be programmed by 3 external resistors.
For low noise, high CMRR, and low drift the AD625JN is the most cost effective instrumentation amplifier solution available. An additional three resistors allow the user to set any gain from 1 to 10,000. The error contribution of the AD625JN is less than 0.05% gain error and under 5 ppm/°C gain TC; performance limitations are primarily determined by the external resistors. Common-mode rejection is independent of the feedback resistor matching. A software programmable gain amplifier (SPGA) can be configured with the addition of a CMOS multiplexer (or other switch network), and a suitable resistor network. Because the ON resistance of the switches is removed from the signal path, an AD625 based SPGA will deliver 12-bit precision, and can be programmed for any set of gains between 1 and 10,000, with completely user selected gain steps.
2. A 12-bit software programmable gain amplifier can be configured using the AD625, a CMOS multiplexer and a resistor network. Unlike previous instrumentation amplifier designs, the ON resistance of a CMOS switch does not affect the gain accuracy. 3. The gain accuracy and gain temperature coefficient of the amplifier circuit are primarily dependent on the user selected external resistors. 4. The AD625 provides totally independent input and output offset nulling terminals for high precision applications. This minimizes the effects of offset voltage in gain-ranging applications. 5. The proprietary design of the AD625 provides input voltage noise of 4 nV/√Hz at 1 kHz. 6. External resistor matching is not required to maintain high common-mode rejection.
For the highest precision the AD625C offers an input offset voltage drift of less than 0.25 µV/°C, output offset drift below 15 µV/°C, and a maximum nonlinearity of 0.001% at G = 1. All grades exhibit excellent ac performance; a 25 MHz gain bandwidth product, 5 V/µs slew rate and 15 µs settling time. The AD625 is available in three accuracy grades (A, B, C) for industrial (–40°C to +85°C) temperature range, two grades (J, K) for commercial (0°C to +70°C) temperature range, and one (S) grade rated over the extended (–55°C to +125°C) temperature range. REV. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
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