Tunable Linear OTA Using Feedback Current Mirrors
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Solution Overview
Problem
Conventional operational transconductance amplifiers (OTAs) face challenges in achieving adjustable and linear transconductance, as the transconductance is either fixed due to a constant resistor or becomes non-linear when adjusted through varying transistor on-resistance.
Innovation Solution
A tunable, linear operational transconductance amplifier design incorporates a differential voltage to current conversion unit and current amplification units with operational amplifiers and CMOS transistors, utilizing control voltages to adjust the transconductance while maintaining linearity through a coupling resistor and current mirrors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a constant resistor is used to determine transconductance, then the transconductance is linear, but it is not easily adjustable
Solution Approach 1:
The patent changes the parameter of the coupling element from a fixed resistor to a transistor whose on-resistance can be adjusted by a control voltage VT. This allows the transconductance to be tuned by varying VT while maintaining the linear relationship between the control voltage and the output current through the transistor's operation in the saturation region.
2Adaptability or versatility
If coupling transistors are used to adjust transconductance, then the transconductance is tunable, but it becomes non-linear
Solution Approach 1:
The patent introduces feedback mechanisms through the current mirror circuits and the coupling between the transistors. The control voltage VT is applied to both transistors 204 and 208, and their drain currents are mirrored and combined, creating a feedback effect that stabilizes the transconductance relationship and reduces non-linearity caused by individual transistor variations.
3Adaptability or versatility
If coupling transistors are used to tune transconductance, then the transconductance is adjustable, but the on-resistance varies non-linearly introducing non-linearity and decreasing accuracy
Solution Approach 1:
The patent merges the functions of multiple transistors (204, 208, 212, 216) and current mirrors into a unified circuit configuration. The combined effect of these components creates a more stable and accurate transconductance relationship, where the non-linearities of individual components are compensated by the overall circuit architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution allows for precise tuning of transconductance with minimal non-linearity, as demonstrated by the linear response and low harmonic distortion across varying control voltages, ensuring high accuracy and adaptability.
Implementation Method 1
A differential voltage to current conversion unit is adapted to generate first and second output signals at respective first and second output nodes responsive to first and second differential input signals
Implementation Method 2
A first current mirror 128 includes CMOS transistors 136 and 140. The current mirror 128 amplifies the current Ii+ to generate a current Io+. A second current mirror 132 includes CMOS transistors 144 and 148. The current mirror 132 amplifies the current Ii− to generate a current Io−.
Data Source
AI summary
A tunable, linear operational transconductance amplifier includes a differential voltage to current conversion unit adapted to generate first and second output signals at respective first and second output nodes responsive to first and second differential input signals. A first current amplification unit is adapted to generate a third output signal responsive to the first output signal and first and second control signals. A second current amplification unit is adapted to generate a fourth output signal responsive to the second output signal and the first and second control signals.