Differential Amplifier Passive Coupling for DC Offset Compensation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Differential amplifiers face significant challenges in reducing DC offset at their output nodes, especially when operating in open loop configurations, which affects dynamic range and linearity, and existing solutions either compromise on gain, introduce complexity, or are not suitable for wide-band applications.

Innovation Solution

An offset feedback differential amplifier with a DC offset negative feedback circuit that uses a passive coupling circuit, either a capacitor or a resistor, to independently compensate for DC offsets without affecting the high impedance of the input nodes, allowing for internal compensation without external components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If external feedback components are used to reduce DC offset, then DC offset is reduced, but input impedance is lowered and circuit complexity increases

Engineering Contradiction:

ImproveDC offsetVSAvoidcircuit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The differential amplifier uses its own internal components (internal capacitors and transistors) to generate the offset compensation signal, eliminating the need for external feedback components. The internal capacitor stores the offset voltage and the internal transistors switch between sampling and compensation phases, making the system self-sufficient and reducing external component requirements.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The offset compensation circuit is nested within the differential amplifier structure itself, with the capacitor and switching transistors integrated into the amplifier's internal architecture. This nesting allows the compensation function to be embedded without adding external circuitry, thereby reducing overall circuit complexity while maintaining effectiveness.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Object-affected harmful factors

If external feedback components are used to reduce DC offset, then DC offset is reduced, but input impedance is lowered

Engineering Contradiction:

ImproveDC offsetVSAvoidinput impedance

Core Design Contradiction:

Object-affected harmful factorsVSDifficulty of detecting and measuring

Solution Approach 1:

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The harmful DC offset is extracted and stored separately in an internal capacitor during the sampling phase, then removed from the output during the compensation phase. This extraction mechanism allows offset reduction without requiring external feedback paths that would load the input and reduce input impedance.

Inventive Principle:

Principle #2Taking out (Extraction)

3Object-affected harmful factors

If trimming is used to compensate DC offset, then DC offset is reduced, but additional testing cost is introduced and temperature drift is not compensated

Engineering Contradiction:

ImproveDC offsetVSAvoidtesting cost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The offset compensation is dynamic rather than static - the circuit automatically samples the offset voltage and updates the compensation signal continuously through periodic switching between sampling and compensation phases. This dynamic operation allows the system to adapt to temperature drift and aging effects without requiring manual trimming or additional testing.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The circuit implements automatic feedback by continuously monitoring the offset voltage through the sampling phase and applying corrective compensation through the compensation phase. This self-correcting feedback mechanism eliminates the need for manual trimming procedures and associated testing costs, while providing continuous compensation for drift.

Inventive Principle:

Principle #23Feedback

4Object-affected harmful factors

If high value resistances are used in Miller integrator, then DC offset is reduced, but amplifier gain is reduced and low pass filter effect occurs

Engineering Contradiction:

ImproveDC offsetVSAvoidamplifier gain

Core Design Contradiction:

Object-affected harmful factorsVSPower

Solution Approach 1:

The circuit uses periodic phase transitions between sampling mode and compensation mode through switching transistors. During the sampling phase, the capacitor charges to the offset voltage; during the compensation phase, the capacitor discharges to cancel the offset. This time-domain switching approach allows offset reduction without requiring high-value resistors that would attenuate the signal or create low-pass filtering effects.

Inventive Principle:

Principle #36Phase transitions

Data Source

PatentUS11018640B2Differential amplifier, corresponding integrated circuit, system, instrumentation amplifier and method

Publication Date: 2021.05.25 STMICROELECTRONICS SRL

AI summary

A differential amplifier includes: first and second input nodes; first and second output nodes; first and second supply nodes; first and second offset compensation nodes; first and second amplifier staged configured to generate first and second output voltages at the first and second output nodes as a function of first and second input voltages of the first and second input nodes and first and second offset compensation voltages of the first and second offset compensation nodes; and a feedback circuit configured to generate the first and second offset compensation voltages as a function of the first and the second output voltages. The feedback circuit includes: a coupling circuit coupled between the first and second offset compensation nodes, wherein the coupling circuit comprises one or more passive electric components.