Source Follower Bias Tracking for PVT-Stable Linearity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional source followers are sensitive to PVT variations, leading to significant second harmonic distortion due to asymmetry in drain-to-source voltage variations, which degrades their linearity and performance.
Innovation Solution
Incorporating a DC tracking circuit that sets a second DC voltage at a specific level relative to a first DC voltage, using transistors and operational amplifiers to maintain symmetry in drain-to-source voltages, thereby reducing second harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single-input-ended source follower is used, then the circuit is simple, but second harmonic distortion is significant due to PVT variations
Solution Approach 1:
The source follower is divided into two symmetric branches: a first branch with a first transistor and first current source, and a second branch with a second transistor and second current source. This segmentation creates symmetry that cancels second harmonic distortion while maintaining circuit functionality.
Solution Approach 2:
The patent introduces asymmetric current sources with different DC voltage levels (first DC voltage and second DC voltage) to compensate for PVT variations. The DC tracking circuit dynamically adjusts these voltages to maintain symmetry in drain-to-source voltage variations, effectively canceling second harmonic distortion.
2Ease of operation
If drain-to-source voltage variations are not symmetric, then the circuit operation is simple, but second harmonic distortion increases
Solution Approach 1:
A DC tracking circuit is implemented to monitor and track the DC voltage levels in both branches. The circuit uses feedback mechanisms to dynamically adjust the current source DC voltages, ensuring that drain-to-source voltage variations remain symmetric and second harmonic distortion is minimized.
Solution Approach 2:
The patent dynamically changes the DC voltage parameters of the current sources to maintain symmetry. The first current source operates at a first DC voltage level while the second current source operates at a second DC voltage level, with these parameters being continuously adjusted by the DC tracking circuit to compensate for PVT variations.
Data Source
AI summary
A source follower with an input node and an output node includes a first transistor, a second transistor, and a DC (Direct Current) tracking circuit. The first transistor has a control terminal, a first terminal coupled to a first node, and a second terminal coupled to a second node. The second transistor has a control terminal, a first terminal coupled to a ground voltage, and a second terminal coupled to the first node. The DC tracking circuit sets the second DC voltage at the second node to a specific level. The specific level is determined according to the first DC voltage at the first node. The output node of the source follower is coupled to the first node.