Class AB differential current conveyor input stage for a fully differential current feedback amplifier

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Fully differential amplifiers face limitations in bandwidth due to parasitic capacitance and noise sensitivity, especially in voltage feedback architectures, and current feedback techniques have not been effectively integrated due to challenges in developing low input impedance, fully differential input stages with good common mode voltage rejection.

Innovation Solution

A current feedback fully differential amplifier design with a differential current conveyor input stage that replicates differential input currents at high impedance outputs, using low impedance inputs and high impedance buffers to isolate external loading, achieving inherent common mode signal rejection and reduced sensitivity to parasitic capacitance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If voltage feedback architecture is used, then common mode reference control is achieved, but bandwidth is limited due to parasitic capacitance

Engineering Contradiction:

Improvecommon mode reference controlVSAvoidbandwidth

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent introduces a differential current conveyor as an intermediary device between the input stage and the output stage. This current conveyor acts as a mediator that transforms the voltage feedback architecture into a current feedback architecture, thereby eliminating the bandwidth limitation imposed by parasitic capacitance while maintaining common mode reference control capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the fundamental operating parameter of the feedback mechanism from voltage feedback to current feedback. By using a differential current conveyor that senses and replicates differential input currents rather than voltages, the system achieves bandwidth independence from parasitic capacitance while preserving common mode rejection through current-based common mode feedback.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If voltage feedback architecture is used, then feedback control is achieved, but noise sensitivity increases

Engineering Contradiction:

Improvefeedback controlVSAvoidnoise sensitivity

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent substitutes the voltage feedback mechanism with a current feedback mechanism. By replacing voltage sensing and feedback with current sensing and feedback through the differential current conveyor, the system achieves feedback control while being less sensitive to noise, as current feedback inherently rejects voltage noise at the input terminals.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Speed

If current feedback technique is integrated, then bandwidth is extended, but input stage complexity increases

Engineering Contradiction:

ImprovebandwidthVSAvoidinput stage complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The patent segments the amplifier into distinct functional blocks: a differential current conveyor input stage, intermediate buffering stages, and output stages. This segmentation allows the complex current feedback functionality to be isolated to specific modules, making the overall design more manageable and implementable despite the increased complexity.

Inventive Principle:

Principle #1Segmentation

4Object-affected harmful factors

If low input impedance is used, then parasitic capacitance sensitivity is reduced, but common mode voltage rejection becomes difficult to achieve

Engineering Contradiction:

Improveparasitic capacitance sensitivityVSAvoidcommon mode voltage rejection

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent employs asymmetric configuration in the differential current conveyor where the two input terminals have different impedance characteristics. The inverting input terminal has low impedance to reduce parasitic capacitance sensitivity, while the non-inverting input terminal is configured to maintain common mode voltage rejection capability through the differential current sensing mechanism.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The differential current conveyor serves multiple functions simultaneously: it provides low impedance at the inverting input to reduce parasitic capacitance effects, maintains common mode voltage rejection through differential current sensing, and enables current feedback operation. This multi-functionality resolves the contradiction between low input impedance and common mode rejection.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS7479831B2Class AB differential current conveyor input stage for a fully differential current feedback amplifier

Publication Date: 2009.01.20 NAT SEMICON CORP

AI summary

Disclosed herein is technology for, among other things, a current feedback fully differential amplifier. The amplifier includes an input stage operable to sense an input current at a first terminal and a second terminal. The input stage includes a first buffer having an input coupled with the first terminal and an output coupled with said the terminal. The input stage further includes a second buffer having an output coupled with the first terminal and an input coupled with the second terminal.