Self-Biased Op-Amp Common-Mode Feedback for Rail-to-Rail Inputs

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional operational amplifiers face challenges in maintaining DC bias voltages and reducing supply current fluctuations when switching between differential input pairs, leading to inefficiencies and increased power consumption.

Innovation Solution

The implementation of a self-biased common-mode feedback circuit coupled with folded cascode transistors in an operational amplifier design, which allows for rail-to-rail input operation and efficient current management by preventing significant changes in common-mode voltage and supply current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If conventional common-mode feedback circuit is included to maintain DC bias voltages during switching, then bias voltage stability is improved, but supply current increases significantly during switching

Engineering Contradiction:

ImproveDC bias voltage stabilityVSAvoidsupply current consumption

Core Design Contradiction:

Stability of the object's compositionVSUse of energy by moving object

Solution Approach 1:

The common-mode feedback circuit generates its own bias current automatically based on the output common-mode voltage level, eliminating the need for external bias current sources. The circuit self-regulates by sensing the output common-mode voltage and adjusting the bias current accordingly, achieving both stability and energy efficiency

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The bias current magnitude is dynamically adjusted based on the output common-mode voltage level. When output common-mode voltage changes during input pair switching, the feedback circuit automatically modifies the bias current to maintain stability while minimizing power consumption variations

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If rail-to-rail input operation is implemented using two parallel differential input pairs, then input voltage range is improved, but DC bias voltage changes significantly during switching

Engineering Contradiction:

Improveinput voltage rangeVSAvoidDC bias voltage stability

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

A common-mode feedback circuit continuously monitors the output common-mode voltage and adjusts the bias current to maintain constant DC bias voltages. This feedback mechanism compensates for the inherent bias voltage changes that occur when switching between parallel differential input pairs, enabling rail-to-rail operation with stable bias conditions

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7564308B1Self-biased operational amplifier

Publication Date: 2009.07.21 NAT SEMICON CORP

AI summary

An operational amplifier in accordance with one embodiment of the invention includes folded cascode transistors and a self-biased common-mode feedback circuit coupled to the folded cascode transistors. The operational amplifier can include an output stage coupled to the self-biased common-mode feedback circuit and the folded cascode transistors.