Extending Rail-to-Rail Output Range for Fully Differential Amplifiers to Include True Zero Volts


Design files


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

A fully assembled board has been developed for testing and performance validation only, and is not available for sale.

Design files & products

Design files

Download ready-to-use system files to speed your design process.

TIDU187.PDF (2291 K)

Reference design overview and verified performance test data

TIDC353.ZIP (1101 K)

Detailed schematic diagram for design layout and components

TIDR460.PDF (64 K)

Detailed schematic diagram for design layout and components

TIDR494.PDF (61 K)

Complete listing of design components, reference designators, and manufacturers/part numbers

TIDC352.ZIP (182 K)

Design file that contains information on physical board layer of design PCB


Includes TI products in the design and potential alternatives.

Charge pumps (inductorless)

LM7705Low Noise Negative Bias Generator

Data sheet document-pdfAcrobat PDF open-in-new HTML
Fully differential amplifiers

THS4531AUltra Low Power, RRO, Fully-Differential Amplifier

Data sheet document-pdfAcrobat PDF open-in-new HTML

Technical documentation

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Type Title Date
Design guide Extending Rail-to-Rail Output Range for Fully Differential Amps Design Guide Apr. 21, 2014

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