Cross-Coupled Differential Amplifier for CLM Distortion Reduction
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Solution Overview
Problem
Differential source follower circuitry suffers from gain loss and limited output impedance due to channel length modulation (CLM) effects, leading to degraded linearity and harmonic distortion.
Innovation Solution
A cross-coupling configuration of auxiliary transistors is introduced to enhance gain and improve linearity without additional power consumption, utilizing a differential amplifier circuit with main and auxiliary transistors connected in specific input and current paths, and controlled by intermediate circuitry to maintain constant current sums.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If source follower circuitry is used as a voltage buffer, then high input impedance is achieved, but gain loss occurs due to channel length modulation effects
Solution Approach 1:
The circuit is divided into a main source follower path and an auxiliary transconductance path. The auxiliary path processes the input signal separately and combines it with the main path output, allowing gain enhancement without affecting the high input impedance of the source follower stage.
Solution Approach 2:
An auxiliary transconductance circuit acts as an intermediary to compensate for gain loss. This auxiliary circuit converts the input voltage signal to a current signal, processes it through a high-gain transconductance stage, and converts it back to voltage, thereby restoring and enhancing the overall gain while preserving the source follower's high input impedance characteristic.
2Device complexity
If conventional source follower circuitry is used, then circuit simplicity is maintained, but linearity is degraded due to CLM effect and output impedance variation
Solution Approach 1:
The amplification function is segmented into two independent paths: the main source follower path maintains simplicity and high input impedance, while the auxiliary transconductance path is specifically designed to provide linearization through its high output impedance current source configuration.
Solution Approach 2:
The auxiliary transconductance circuit changes the operating parameters by using a high output impedance current source to bias the transconductance device, which operates in a region that provides improved linearity. This parameter optimization reduces the impact of CLM effects and output impedance variation on overall circuit linearity.
3Manufacturing precision
If auxiliary transconductance circuit is added to enhance gain, then distortion is reduced, but power consumption increases
Solution Approach 1:
The auxiliary transconductance circuit is merged with the main source follower circuit through signal combination at the output node. Both circuits process the same input signal but through different paths, and their outputs are combined to achieve distortion reduction. The circuits share common biasing resources and operate in a complementary manner to minimize additional power consumption.
Data Source
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AI summary
Differential amplifier circuitry (312) configured to generate a differential output signal between first and second output nodes based on a differential input signal provided between first and second input nodes, the circuitry comprising: first (106) and second (206) main transistors of a given conductivity type; and first (104) and second (204) auxiliary transistors of an opposite conductivity type to the given conductivity type, wherein the first (106) and second (206) main transistors are connected along first and second main current paths which pass between first and second main voltage reference nodes and the first and second output nodes, respectively, with their source terminals connected to the first and second output nodes, respectively, and with their gate terminals connected to be controlled by component input signals of the differential input signal provided at the first and second input nodes, respectively; and the first (104) and second (204) auxiliary transistors are connected along first and second auxiliary current paths which pass between first and second auxiliary voltage reference nodes and the first and second output nodes, respectively, with their drain terminals connected to the first and second output nodes, respectively, and with their gate terminals connected to be controlled by the component input signals of the differential input signal provided at the second and first input nodes, respectively.