Current-Mode Transconductor Tuning for Consistent gm Matching
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Solution Overview
Problem
Conventional transconductor tuning devices face challenges in maintaining accurate transconductance due to changes in power supply voltage, temperature, and manufacturing processes, and are affected by ground resistance and DC offset errors, leading to inconsistent transconductance levels across multiple transconductors.
Innovation Solution
A transconductor tuning device that utilizes a tuning current and reference voltage, generated by a current mirror circuit and external resistor, to tune transconductance, eliminating the impact of ground resistance and DC offset errors, and ensuring consistent transconductance across multiple transconductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a control voltage Vb is generated using an operational amplifier and applied to multiple transconductors, then the transconductance can be tuned, but the transconductance becomes inconsistent across different transconductors due to ground resistance and DC offset errors
Solution Approach 1:
The patent replaces the voltage-based tuning system (using operational amplifiers and control voltages) with a current-based tuning system. The tuning current is distributed to multiple transconductors through current mirrors, eliminating the ground resistance and DC offset problems inherent in voltage distribution. This substitution of the control mechanism (from voltage to current) resolves the inconsistency issue while maintaining tuning capability.
2Productivity
If the transconductor layout area is increased to accommodate multiple transconductors, then more transconductors can be tuned, but the transconductance difference increases due to mismatching among MOS transistors
Solution Approach 1:
The patent changes the control parameter from voltage to current. By using current mirrors to distribute the tuning current, the system achieves better matching across multiple transconductors even when they are spatially separated. The current-based approach is less sensitive to layout variations and MOS transistor mismatches compared to voltage-based approaches, thereby maintaining manufacturing precision while increasing the number of tunable transconductors.
3Adaptability or versatility
If a voltage-based tuning circuit is used, then the transconductance can be adjusted, but the tuning accuracy is degraded by DC offset of the operational amplifier
Solution Approach 1:
The patent eliminates the operational amplifier from the tuning circuit by substituting the voltage-based control mechanism with a current-based mechanism. The tuning current is generated and distributed using current mirrors and resistors, which do not suffer from DC offset errors. This substitution removes the source of tuning inaccuracy while preserving the ability to adjust transconductance.
Data Source
AI summary
A transconductor tuning device tuning a transconductance using a current. The transconductor tuning device includes a tuning section that applies a tuning current and a reference voltage to a transconductor converting an input voltage signal into a current signal and thereby tunes a level of transconductance. The tuning section includes a tuning current generator that converts a bias signal supplied from a bias current source into a certain level of tuning current and outputs the tuning current to the transconductor. The transconductor includes a control voltage generator that generates a certain level of control voltage using the tuning current. Accordingly, the transconductance of the plurality of transconductors are tuned at the same level.