Transconductor With Adaptive Stage For Linearity
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Solution Overview
Problem
Conventional transconductance stages in analog circuits, such as mixers and low noise amplifiers, suffer from limited linearity due to their narrow input voltage range, leading to distortion issues in RFICs for wireless communications.
Innovation Solution
A transconductor design incorporating a primary transconductance stage and an adaptive transconductance stage coupled in series, along with a bias circuit, to provide a wide input voltage range by compensating nonlinearity through harmonic cancellation and full switching operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional differential pair circuit is used as a transconductance stage, then the circuit structure is simple, but the input voltage range is narrow and linearity is poor
Solution Approach 1:
The transconductance stage is divided into two separate stages: a primary transconductance stage and an adaptive transconductance stage. The primary stage provides the main transconductance function, while the adaptive stage is specifically designed to cancel third-order harmonic distortion. This segmentation allows each stage to be optimized for its specific function, resolving the contradiction between structural simplicity and linearity performance.
Solution Approach 2:
An adaptive transconductance stage is introduced as an intermediary component between the input and output. This intermediate stage generates an output current that is specifically designed to cancel the third-order harmonic distortion produced by the primary transconductance stage, thereby improving overall linearity without requiring complete redesign of the entire circuit.
2Ease of operation
If the differential input voltage amplitude is increased to expand the input voltage range, then the input voltage range is widened, but the linearity is lost due to saturation region operation
Solution Approach 1:
The adaptive transconductance stage performs preliminary anti-action by generating a current that preemptively cancels the third-order harmonic distortion before it can degrade the output signal. This allows the primary transconductance stage to operate with larger input voltage amplitudes without sacrificing linearity, as the distortion is continuously compensated in real-time.
Solution Approach 2:
The adaptive transconductance stage implements a form of feedback by continuously monitoring the output of the primary stage and generating a compensating current that cancels distortion components. This feedback mechanism enables the system to maintain linearity across a wider input voltage range by dynamically adjusting to prevent distortion accumulation.
Data Source
AI summary
A transconductor to convert an input voltage to an output current, includes: a primary transconductance stage to provide the output current from the input voltage and a driving current; an adaptive transconductance stage coupled in series with the primary transconductance stage to generate the driving current from the input voltage; and a bias circuit coupled to provide a primary bias voltage to the primary transconductance stage and an adaptive bias voltage to the adaptive transconductance stage.