Dynamic-Bias Transconductance Amplifier for Linear Output Current
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Solution Overview
Problem
Conventional transconductance amplifiers suffer from errors and reduced linearity due to the transconductance of the transistor in the input stage, and they consume fixed bias current regardless of output current, leading to high power consumption.
Innovation Solution
A transconductance amplifier with a rearranged input stage using multiple transistors and a bias current control circuit to generate output currents based on positive and negative input voltages, reducing errors and linearity issues while dynamically adjusting bias current based on input voltage differences to minimize power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional transconductance amplifier uses a transistor in the input stage to generate output current from input voltage, then the amplifier can perform basic transconductance function, but errors occur due to the transconductance of the transistor itself affecting the drain current
Solution Approach 1:
The input stage is segmented into multiple parallel transistor branches (first transistor branch with third transistor, second transistor branch with fourth transistor) instead of using a single transistor. This segmentation allows the circuit to compensate for individual transistor transconductance variations by combining multiple paths, thereby reducing the impact of any single transistor's non-ideal characteristics on the overall accuracy.
Solution Approach 2:
A first resistor is introduced as an intermediary element connected between the first and second transistors. This resistor serves as a mediator to balance and regulate the currents flowing through the parallel transistor branches, compensating for transconductance mismatches and reducing errors in the output current generation.
2Measurement precision
If a conventional transconductance amplifier uses a transistor in the input stage, then the amplifier can operate, but linearity deteriorates due to the non-linearity characteristic of the transistor's transconductance
Solution Approach 1:
The single non-linear transistor path is divided into multiple parallel transistor branches. By distributing the transconductance function across multiple transistors and combining their outputs, the overall transfer characteristic becomes more linear, as the non-linearities of individual transistors tend to average out in the combined response.
Solution Approach 2:
The circuit topology is changed from a single transistor path to multiple parallel paths with resistive coupling. This parameter change in the circuit architecture fundamentally alters the transfer characteristic, transforming the strongly non-linear single-transistor behavior into a more linear multi-branch system response.
3Reliability
If a conventional transconductance amplifier uses fixed bias current, then the amplifier can maintain stable operation, but power consumption increases unnecessarily when output current is low
Solution Approach 1:
The bias current is changed from a fixed static value to a dynamic value that automatically adjusts according to the input voltage difference. The bias current control circuit continuously monitors the input voltage and modulates the bias current accordingly, increasing it when large output current is needed and decreasing it when small output current suffices, thus maintaining stable operation while optimizing power consumption.
Solution Approach 2:
A bias current control circuit is introduced that uses feedback from the input voltage to regulate the bias current. The control circuit senses the input voltage difference and adjusts the bias current in real-time, creating a closed-loop system that adapts the power consumption to the actual signal requirements while ensuring stable amplifier operation.
Data Source
AI summary
The present application discloses a transconductance amplifier and a related chip. The transconductance amplifier is configured to generate an output current according to a positive input voltage and a negative input voltage, wherein the transconductance amplifier includes: an input stage, configured to receive the positive input voltage and the negative input voltage and generate a positive output current and a negative output current, wherein the input stage includes: a first transistor, wherein a gate thereof is coupled to the positive input voltage; a second transistor, wherein a gate thereof is coupled to the negative input voltage; a first resistor, serially connected between the first transistor and the second transistor; a third transistor, wherein a source of the third transistor is coupled between the first resistor and the first transistor, and a drain of the third transistor is configured to output the positive output current; and a fourth transistor.