OTA Linearization Circuit Using Distortion Transconductance Overlap
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Solution Overview
Problem
Conventional triode region type operational transconductance amplifiers (OTAs) face challenges in maintaining a wide linear input range and constant transconductance at low power supply voltages, especially when using differential pair input transistors with short channel lengths, which leads to reduced frequency characteristics and nonlinearity.
Innovation Solution
A linearization apparatus for triode region type OTAs is introduced, comprising a first transconductor unit generating basic transconductance and a second transconductor unit generating distortion transconductance, which overlap to extend the linear range of the final transconductance, using a combination of NMOS and PMOS transistors and amplifiers to maintain linearity and adjust drain-source voltages for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If transistors with short channel lengths are used to improve frequency characteristics, then speed is improved, but linearity deteriorates
Solution Approach 1:
The patent divides the transconductance generation into two separate functional units: a first transconductor unit for generating basic transconductance and a second transconductor unit for generating distortion transconductance. This segmentation allows each unit to be optimized independently - the first unit can use short-channel transistors for high frequency performance while the second unit compensates for linearity errors, thereby resolving the contradiction between speed and linearity.
Solution Approach 2:
The second transconductor unit acts as an intermediary that generates distortion transconductance to compensate for the non-linearity introduced by the first transconductor unit. This intermediary component corrects the linearity degradation caused by short-channel effects while preserving the high-frequency characteristics of the primary transconductor.
2Manufacturing precision
If a wide linear input range is achieved by increasing drain-source voltage, then linearity is improved, but power consumption increases
Solution Approach 1:
The patent changes the operational parameters of the transistors by applying specific gate voltages (Vb1, Vb2, Vb3, Vb4) to the transconductor units. By carefully controlling these gate voltages, the transistors operate in optimal regions that provide both wide linear input range and low power consumption, eliminating the need to increase drain-source voltage for linearity improvement.
Solution Approach 2:
The second transconductor unit provides a feedback mechanism that generates distortion transconductance to compensate for non-linearity. This feedback approach maintains linearity across a wide input range without requiring increased power consumption, as the correction is achieved through intelligent signal processing rather than brute-force voltage increases.
3Manufacturing precision
If distortion transconductance is added to extend linear range, then linearity is improved, but device complexity increases
Solution Approach 1:
The patent merges the distortion compensation function into the existing transconductor structure by adding a second transconductor unit that operates in parallel with the first. Both units share common input signals and are integrated into a unified output stage, achieving linearity extension without creating separate complex compensation circuits.
Solution Approach 2:
The second transconductor unit serves multiple functions: it generates distortion transconductance for linearity compensation, operates with the same input signals as the first unit, and integrates seamlessly with the existing circuit architecture. This multi-functionality reduces overall system complexity compared to dedicated compensation circuits.
Data Source
AI summary
Provided is a linearization apparatus of a triode region type operational transconductance amplifier that can provide a wide linear input range even when a differential pair input transistor having a short channel length is used at a low power supply voltage. The linearization apparatus of the triode region type operational transconductance amplifier includes: a first transconductor unit for receiving differential pair input voltages through differential pair input transistors and generating a basic transconductance; and a second transconductor unit for receiving the same differential pair input voltages, generating distortion transconductances, and overlapping the basic transconductace with the distortion transconductance for extending a linear range of a final transconductance.