Complementary Self-Biased Differential Receiver for Low-Voltage PVT Stability

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Solution Overview

Problem

Conventional self-biased differential amplifiers face challenges in low voltage operation due to low speed, large circuit area requirements, limited output swing, and intolerance to variations in process, voltage, and temperature (PVT), which hinder their use in small electronic devices.

Innovation Solution

The implementation of a complementary self-biased differential amplifier with a virtual positive and negative supply voltage system, where the startup circuit compensates for defect currents and ensures reliable operation by modulating bias voltages, allowing the amplifier to operate effectively over a wider range of input signals and improving PVT tolerance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If conventional self-biased differential amplifiers are used for low voltage operation, then power consumption is reduced, but speed deteriorates and circuit area increases

Engineering Contradiction:

Improvepower consumptionVSAvoidamplifier speed

Core Design Contradiction:

Use of energy by moving objectVSSpeed

Solution Approach 1:

The amplifier is divided into separate positive and negative differential sides, each with dedicated current sources and biasing circuits. This segmentation allows independent optimization of each side's performance characteristics, enabling low voltage operation while maintaining speed through tailored biasing conditions on each side.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The startup circuit pre-establishes the correct biasing conditions and current flow before the amplifier begins normal operation. By preliminarily setting the operating point and ensuring proper voltage levels at critical nodes, the amplifier can immediately achieve high-speed performance when powered on, rather than requiring slow settling transients.

Inventive Principle:

Principle #10Preliminary action

2Use of energy by moving object

If conventional self-biased differential amplifiers are used for low voltage operation, then power consumption is reduced, but circuit area increases

Engineering Contradiction:

Improvepower consumptionVSAvoidcircuit area

Core Design Contradiction:

Use of energy by moving objectVSArea of moving object

Solution Approach 1:

The biasing circuits for the positive and negative sides are merged into a unified complementary structure where current sources and biasing elements serve both sides simultaneously. This combining eliminates redundant components and reduces the total circuit area while maintaining the low voltage operation capability that drives the power consumption benefits.

Inventive Principle:

Principle #5Merging (Combining)

3Device complexity

If conventional self-biased amplifiers are used, then circuit simplicity is maintained, but output swing is limited

Engineering Contradiction:

Improvecircuit simplicityVSAvoidoutput swing

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The invention changes the biasing parameters and current source configurations to enable larger voltage excursions at the output nodes. By adjusting the operating point and current levels, the amplifier achieves increased output swing capability while preserving the fundamental self-biased topology that maintains circuit simplicity.

Inventive Principle:

Principle #35Parameter changes

4Device complexity

If conventional self-biased amplifiers are used, then design simplicity is maintained, but PVT tolerance deteriorates

Engineering Contradiction:

Improvedesign simplicityVSAvoidPVT tolerance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The complementary self-biased structure incorporates implicit feedback mechanisms where the biasing voltages and currents automatically adjust in response to process, voltage, and temperature variations. The interdependent biasing of positive and negative sides creates self-correcting behavior that maintains stable operation across PVT conditions while preserving design simplicity.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8823454B2Fully complementary self-biased differential receiver with startup circuit

Publication Date: 2014.09.02 NXP USA INC

AI summary

In accordance with at least one embodiment, an improved voltage headroom self-biased receiver is provided. In accordance with at least one embodiment, tail current sources are biased so as to be cross-coupled with respect to each other. In accordance with at least one embodiment, startup control is provided to counter defect-induced current and to ensure the circuit can function properly even with large amounts of defect current. In accordance with at least one embodiment, a positive type (p type) channel metal oxide semiconductor (PMOS) tail current transistor is modulated by a negative type (n type) channel metal oxide semiconductor (NMOS) differential pair virtual negative supply voltage and a NMOS tail current transistor is modulated by a PMOS differential pair virtual positive supply voltage. The amplifier's output common mode is thus self correcting to p type to n type transistor strength differences.