MOS Transconductance Amplifier with Stable Linearity Tuning
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Solution Overview
Problem
Conventional transconductance amplifiers experience a deterioration in linearity between input voltage and output current when the tuning voltage is adjusted, limiting the range of transconductance adjustment.
Innovation Solution
A transconductance amplifier design that maintains a constant difference between the tuning voltage and common voltage, using a differential pair of MOS transistors operating in triode and saturation regions, with a voltage generator circuit and differential-pair input voltage generator circuit to ensure the common voltage is adjusted accordingly, thereby maintaining linearity across a wider range of operating input voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the tuning voltage Vctrl is increased to adjust the transconductance, then the transconductance adjustment range is improved, but the linearity between input voltage and output current deteriorates
Solution Approach 1:
The invention changes the operating parameters of the MOS transistors by controlling their gate voltages through amplifiers. Specifically, the gate voltage of the third MOS transistor is controlled by the first amplifier, and the gate voltage of the fourth MOS transistor is controlled by the second amplifier, allowing the transconductance to be adjusted while maintaining proper operating conditions for linearity
Solution Approach 2:
The invention employs feedback mechanisms where the amplifiers monitor the drain voltages and adjust the gate voltages of the cascode-connected MOS transistors accordingly. This feedback ensures that the drain voltages remain constant despite input variations, thereby maintaining linearity across the transconductance adjustment range
2Manufacturing precision
If the range of operating input voltages is narrowed or the tuning voltage variation is reduced to maintain linearity, then the linearity is improved, but the transconductance adjustment capability is limited
Solution Approach 1:
The invention makes the gate voltages of the cascode-connected MOS transistors dynamic by using amplifiers that actively adjust these voltages based on the input signal and tuning voltage. This dynamic control allows the transconductance to be adjusted over a wide range while maintaining linearity, as the amplifiers continuously adapt the operating point of the MOS transistors
Data Source
AI summary
Provided is a transconductance amplifier capable of suppressing variation in the range of a linear relationship between an input voltage and an output current depending on the magnitude of a tuning voltage Vctrl, thereby adjusting transconductance over a wider range of operating input voltages. The transconductance amplifier is configured by a differential pair formed of MOS transistors (111, 112) having a common source, MOS transistors (113, 114), amplifiers (106, 107), a voltage generator circuit (100), and a differential-pair input voltage generator circuit (120). An input differential common voltage Vcm of all differential signals inputted to the differential pair is adjusted so that a difference between Vcm and Vctrl is equal to a constant, in accordance with a change in the tuning voltage Vctrl that controls the transconductance. This enables keeping constant the range in which the transconductance amplifier can achieve good linearity.