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Build an Instrumentation Amplifier with Picoamp-Level Input Bias Current

₹1,760

The LT1079 draws very little supply current while still delivering low offset voltage and low noise. This makes the module well-suited to battery-powered instrumentation and sensor front-ends where both precision and low power draw matter.


 


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The LT1079 draws very little supply current while still delivering low offset voltage and low noise. This makes the module well-suited to battery-powered instrumentation and sensor front-ends where both precision and low power draw matter.

 

Specs and Features

  • Supply voltage: 9 V DC
  • Output range: 4 mV to 8.2 V
  • Key IC: LT1079 micropower quad op amp
  • Gain: (1 + 2R3/RG) × R9/R2 = 100
  • Input bias current: typically less than 150 pA
  • Input resistance: 3R = 30 MΩ
  • Gain bandwidth: 1.8 MHz
  • Onboard power LED
  • Header connectors for input, output, and power
  • PCB dimensions: 36.99 mm x 16.19 mm

 

How It Works

The LT1079 is a micropower quad op amp in a standard 16-pin package. It is optimized for 5 V single-supply operation, though ±15 V operation is also specified. Most micropower op amps sacrifice precision, noise, speed, or output drive to save current. In contrast, the LT1079 cuts supply current without sacrificing performance.

The LT1079 achieves the lowest offset voltage of any dual or quad non-chopper-stabilized op amp. Its offset current, noise, slew rate, and gain bandwidth product are two to ten times better than earlier micropower models. Its voltage noise 1/f corner sits at 0.7 Hz—at least three times lower than any monolithic op amp. This provides low-frequency noise performance typically seen only in high-current devices.

The device can run from a single supply as low as one lithium cell or two Ni-Cad batteries. Its input range extends below ground. While sinking current, its all-NPN output stage swings within a few millivolts of ground, eliminating the need for power-consuming pull-down resistors.

On this board, three internal op amps form the instrumentation amplifier signal path. Two serve as input buffers, followed by a difference amplifier that sets an overall gain of 100. The fourth op amp combines with resistors R10, R17, and R18 to form a bias current cancellation loop, removing input bias current before it introduces sensor errors. Bridge resistors R1, R4, R5, R12, R13, and R16 allow the input stage to interface directly with resistive bridge sensors.


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