Transconductance Amplifier Gain Linearization via Copy-Cell Feedback
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Solution Overview
Problem
Transconductance amplifiers exhibit a highly non-linear link between the gate driving voltage and transconductance gain, leading to non-linear variations in gain, which limits their performance.
Innovation Solution
A driving method that uses a copy of the base differential cell to generate a current proportional to the transconductance, allowing for a linear relationship between the control voltage and transconductance gain by adjusting the driving voltage of the degenerative driving transistor, and includes a comparison block to balance current signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a degenerative driving transistor is used to control the transconductance gain, then the gain can be varied, but the link between gate driving voltage and transconductance gain becomes highly non-linear
Solution Approach 1:
The patent introduces a feedback mechanism where a copy of the base differential cell generates a current proportional to the transconductance gain. This feedback current is compared with a reference current, and the difference is used to adjust the gate driving voltage of the degenerative transistor. This closed-loop feedback system linearizes the relationship between control voltage and gain by continuously compensating for non-linearities.
Solution Approach 2:
The patent creates a copy of the base differential cell that replicates the non-linear transconductance characteristics. This copy cell generates a current signal that is proportional to the actual transconductance gain of the amplifier. By using this copied signal for feedback control, the system can measure and compensate for the non-linearities without requiring complex mathematical models or lookup tables.
2Power
If the degenerative driving transistor resistance is reduced to increase transconductance gain, then high gain is achieved, but the control linearity deteriorates
Solution Approach 1:
The feedback loop continuously monitors the actual transconductance gain through the copy differential cell and adjusts the gate driving voltage accordingly. This allows the system to maintain high gain (achieved by low degenerative transistor resistance) while compensating for the resulting non-linearities in real-time, thus preserving control linearity despite the aggressive gain enhancement.
Solution Approach 2:
The patent dynamically changes the operating parameters of the degenerative driving transistor through feedback control. By adjusting the gate driving voltage based on the difference between feedback current and reference current, the system optimizes the transistor's resistance value to maintain both high gain and linear control characteristics across different operating conditions.
Data Source
AI summary
The disclosure relates to a driving method for obtaining a linear gain variation of a transconductance amplifier that includes a first differential transistor cell, with adjustment of a driving voltage value of a degenerative driving transistor of the transconductance amplifier The method includes generating an output current signal of a second differential cell corresponding to the first differential transistor cell of the transconductance amplifier, the output current signal having a linear relationship with a transconductance value of the second differential cell as the driving voltage varies; generating a reference current signal having a linear relationship with a differential input voltage; comparing the output current signal and the reference current signal for adjusting the driving voltage value; and modifying the transconductance value of the second differential cell up to a balance of the current signals.