Nonlinear Transconductance Amplifier With Low Quiescent Current

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Solution Overview

Problem

Existing transconductance amplifiers with nonlinear transconductance (gm) require high quiescent current, which increases complexity, cost, and reduces stability in feedback circuits due to the need for multiple amplifiers with discrete gm levels.

Innovation Solution

A transconductance amplifier design featuring a single amplifier with multiple resistors in series and selectively enabled drive circuits that draw no current until activated, allowing for exponential or nonlinear current output without quiescent current draw, especially suited for feedback loops and high capacitance loads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple transconductance amplifiers are interconnected to achieve nonlinear gm, then the desired nonlinear gm characteristics are achieved, but the quiescent current increases and device complexity increases

Engineering Contradiction:

Improvenonlinear gm characteristicsVSAvoidquiescent current

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The patent applies dynamics by making the transconductance amplifier's gm dynamically variable based on the input voltage differential. A single amplifier's gm is modulated in real-time according to the magnitude of the input voltage, achieving nonlinear gm characteristics without requiring multiple static amplifiers. This dynamic adjustment allows the amplifier to have low quiescent current while providing high gm when needed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the gm parameter of the amplifier dynamically based on the input voltage differential. When the input voltage differential is small, the amplifier operates with low gm for stability; when the input voltage differential is large, the amplifier switches to high gm for rapid response. This parameter change approach eliminates the need for multiple amplifiers with fixed gm levels.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If multiple transconductance amplifiers are interconnected to achieve nonlinear gm, then the desired nonlinear gm characteristics are achieved, but the device complexity and cost increase

Engineering Contradiction:

Improvenonlinear gm characteristicsVSAvoidamplifier interconnection complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent merges the functions of multiple amplifiers into a single amplifier by integrating the nonlinear gm control logic within one device. Instead of interconnecting multiple amplifiers, the invention combines the amplification function with the gm modulation function in a single integrated circuit, reducing device complexity and cost while maintaining the desired nonlinear gm characteristics.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent makes a single amplifier universal by enabling it to perform multiple functions: linear amplification, nonlinear gm modulation, and adaptive response to different input voltage levels. This multi-functionality eliminates the need for multiple specialized amplifiers, reducing system complexity while achieving the same performance benefits.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Speed

If high gm is maintained continuously, then rapid response to load changes is achieved, but stability in feedback circuits deteriorates

Engineering Contradiction:

Improvereaction speed to load changesVSAvoidfeedback circuit stability

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The patent applies dynamics by making the gm variable rather than fixed. The amplifier dynamically adjusts its gm based on the instantaneous input voltage differential, providing low gm for stability during steady-state operation and high gm for rapid response during transient conditions. This dynamic adaptation resolves the contradiction between stability and speed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements periodic action through the oscillating or switching behavior of the gm between low and high states based on the input signal conditions. The amplifier periodically transitions between different gm levels in response to the input voltage differential, achieving both stability during low-differential periods and rapid response during high-differential periods.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentEP3544180B1Transconductance amplifier with nonlinear transconductance and low quiescent current

Publication Date: 2022.06.01 ANALOG DEVICES INT UNLTD CO

Figure 1~3
Figure 2
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AI summary

A composite transconductance amplifier is formed using a single transconductance amplifier with its output connected to a load via one or more resistors in series. The single transconductance amplifier has a linear tranconductance (gm). As the current through the series resistors is increased, the voltage drops across the nodes of the resistors increase. Control terminals of separate drive circuits are connected to the various nodes and successively turn on as the current from the single transconductance amplifier slews more positive. Thus, the effective gm of the composite transconductance amplifier is based on the gm of the single transconductance amplifier and the currents contributed by the successively enabled drive circuits. Therefore, the gm is nonlinear. Pull-down drive circuits are also connected to the resistor nodes to successively pull down the current as the output from the single transconductance amplifier slews negative. The composite transconductance amplifier has low quiescent current.