Open-Loop Programmable Amplifier Gain Compensation for PVT Stability

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Solution Overview

Problem

Open loop programmable amplifiers experience gain variation due to PVT (process, voltage, and temperature) fluctuations, which is challenging to manage effectively, especially in high-speed applications where closed loop architectures are limited by bandwidth and power consumption.

Innovation Solution

A circuit and method that utilize a reference signal generator, gain compensation circuit, and feedback loop to maintain constant gain by adjusting degeneration resistors and bias current in an open loop gain stage amplifier, using CMOS and BiCMOS transistors, with a selector and error amplifier to apply control voltage signals, ensuring transconductance stability across PVT variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If closed loop architecture is used to maintain constant gain, then gain stability over PVT is improved, but bandwidth and power consumption worsen

Engineering Contradiction:

Improvegain stabilityVSAvoidbandwidth

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The gain control function is segmented into multiple independent gain stages, each with its own compensation circuit. This allows each stage to be optimized independently for high-speed operation while collectively providing stable overall gain, resolving the contradiction between gain stability and bandwidth.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An intermediate compensation mechanism is introduced that uses reference voltages and control voltage signals to adjust degeneration resistors and bias currents. This intermediary control system provides gain stability without requiring a full closed-loop feedback path, thereby maintaining high bandwidth while achieving constant gain.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If closed loop architecture is used to maintain constant gain, then gain stability over PVT is improved, but power consumption worsens

Engineering Contradiction:

Improvegain stabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The gain compensation circuit uses self-generated control signals based on reference voltages to automatically adjust and maintain constant gain. This self-service mechanism eliminates the need for external feedback control, reducing power consumption while maintaining gain stability.

Inventive Principle:

Principle #25Self-service

3Speed

If open loop architecture is used for high speed operation, then bandwidth is improved, but gain variation over PVT worsens

Engineering Contradiction:

ImprovebandwidthVSAvoidgain stability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

Preliminary compensation actions are taken by pre-adjusting degeneration resistors and bias currents based on reference voltages before PVT variations affect the amplifier. This proactive gain compensation maintains stability while preserving the high-speed open-loop performance.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention changes key parameters (degeneration resistance values and bias currents) dynamically through control voltage signals to compensate for PVT variations. This parameter adjustment mechanism maintains constant gain while preserving the high bandwidth characteristics of the open-loop architecture.

Inventive Principle:

Principle #35Parameter changes

4Reliability

If degeneration resistors are adjusted to maintain constant gain, then transconductance stability is improved, but circuit complexity worsens

Engineering Contradiction:

Improvetransconductance stabilityVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The gain compensation is applied locally to each gain stage independently through individual control voltage signals. This localized approach maintains transconductance stability in each stage without requiring a complex global control system, thereby reducing overall circuit complexity while achieving the desired stability.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS20200136579A1Gain compensation for an open loop programmable amplifier for high speed applications

Publication Date: 2020.04.30 NXP BV

AI summary

Various embodiments relate to a method and apparatus for maintaining constant gain in an open loop gain stage amplifier, the circuit including a reference signal generator configured to generate a plurality of reference voltages, a gain compensation circuit, including a reference selector configured to select one of the plurality of reference voltages for each of a plurality of gain stages, an error amplifier configured to output a control voltage signal to a selector, a selector configured to select which of a plurality of degeneration resistors in the open loop gain stage amplifier to apply the control voltage signal wherein the voltage signal is applied to the gate of at least one of the plurality of degeneration resistors in the open loop gain stage amplifier.