Extending Rail-to-Rail Output Range for Fully Differential Amplifiers to Include True Zero Volts
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Operational amplifiers (op amps) have been used for decades in signal conditioning circuits and measurement systems. An op amp that has an output spanning from negative to positive supply rail are generally referred to as rail-to-rail output (RRO) op amps. These devices have been used increasingly in portable systems to drive analog to digital converters (ADCs) where reducing power consumption while not sacrificing converter dynamic range is a key concern. While the task calls for the lowest power RRO op amps, circuit designers are finding out that rail-to-rail doesn’t exactly mean rail-to-rail.  In reality the output is limited to a couple hundred millivolts within the rail depending on the loading. This problem is known as headroom and is the result of the RRO architecture. This application report focuses on using a low power RRO fully differential op amp (THS4531A) and low noise negative bias generator (LM7705) to achieve true zero volts in a ground referenced single supply system.

  • Single supply +3V to +5V
  • Extends Differential Amplifier Output to Include 0V
  • Low Noise (Approx 100dB SNR)
  • Low Power (2mW @ 5V)
  • 36MHz of Bandwidth
  • This reference design has been lab tested and is supported with design files and an application report

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TI Devices (2)

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Part Number Name Product Family Sample & Buy Design Kits & Evaluation Modules
LM7705  Low Noise Negative Bias Generator  DC/DC switching regulators  Sample & Buy View Design Kits & Evaluation Modules
THS4531A  Ultra Low Power, RRO, Fully-Differential Amplifier  Amplifiers  Sample & Buy View Design Kits & Evaluation Modules

CAD/CAE symbols

Part # Package | Pins CAD File (.bxl) STEP Model (.stp)
LM7705 Download Download
THS4531A Download

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User guide (1)
Title Type Size (KB) Date
PDF 2291 21 Apr 2014
Design files (4)
Title Type Size (KB) Date
ZIP 1101 02 Apr 2014
ZIP 182 02 Apr 2014
PDF 61 02 Apr 2014
PDF 64 17 Mar 2014

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