Variable Transconductance Circuit With Dual Bias Current Control
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Solution Overview
Problem
Conventional variable transconductance circuits in semiconductor integrated circuits face challenges in achieving wide-range transconductance variation while maintaining low power consumption and compact circuit size, especially under low power supply voltages, which is crucial for optical disk devices that require signal processing across a wide range of signal speeds and amplitudes.
Innovation Solution
A variable transconductance circuit design that includes voltage-current conversion, MOS transistors, and transconductance control circuits with multiple current sources and parallel transistor configurations, allowing for wide-range transconductance variation by controlling bias currents and using current mirrors for efficient transconductance control, enabling up to 100 times variation in transconductance with a low power supply voltage of 3V.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Io is increased by 100 times to allow gm to vary up to 10 times its minimum value, then gm variation range is improved, but power consumption increases and low power supply voltage operation becomes difficult
Solution Approach 1:
The patent applies dynamics by making the transconductance circuit adjustable and adaptable to different operating conditions. The circuit uses two independent current sources (Ia and Ib) that can be dynamically controlled to achieve wide gm variation (up to 100 times) without requiring a 100-fold increase in a single current, thereby enabling flexible adaptation to various signal processing requirements while maintaining low power consumption.
Solution Approach 2:
The patent changes the control parameter from a single current source to two independent current sources (Ia and Ib). By controlling these two parameters separately, the circuit achieves wide gm variation range through the combined effect of both currents, avoiding the need to increase a single current by 100 times and thus reducing power consumption while expanding adaptability.
2Adaptability or versatility
If a plurality of transconductors are connected in parallel to enable wide-range gm variation, then gm variation range is improved, but on-board circuit area increases
Solution Approach 1:
The patent achieves multi-functionality by using two current sources (Ia and Ib) that can independently control different aspects of the transconductance circuit. This universal control mechanism allows a single circuit configuration to achieve wide gm variation range without requiring multiple parallel transconductors, thereby reducing circuit area while maintaining adaptability.
Solution Approach 2:
Instead of increasing circuit area by adding parallel transconductors, the patent changes the control approach to using two adjustable current parameters (Ia and Ib). This parameter-based control achieves the same wide gm variation range with a more compact circuit implementation, effectively reducing on-board circuit area.
3Adaptability or versatility
If Io is increased by 100 times to achieve wide gm variation, then gm variation range is improved, but current consumption increases
Solution Approach 1:
The patent transforms the control mechanism from a single current source requiring 100-fold variation to two current sources (Ia and Ib) that can be independently adjusted. This parameter change allows achieving wide gm variation range through coordinated control of both currents, significantly reducing the total current consumption compared to increasing a single current by 100 times.
Data Source
AI summary
The variable transconductance circuit includes: a voltage-current conversion circuit for outputting a current signal linear with an input voltage signal; first and second MOS transistors for converting the current signal received to a square-root compressed voltage signal; and third and fourth MOS transistors for converting the square-root compressed voltage signal to a linear current signal. A bias current at the first and second MOS transistors and a bias current at the third and fourth MOS transistors are varied to control transconductance.