Cascade Complementary Source Follower With Feedback DC Offset Correction
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Solution Overview
Problem
Conventional source followers fail to accurately follow DC components of input signals due to a difference between output and input common mode voltages, which are identical to the gate-source voltage of the MOS transistor, limiting their ability to replicate the DC component of the input signal.
Innovation Solution
A cascade complementary source follower circuit is introduced, incorporating a source follower circuit with at least two MOS transistors and a feedback circuit that includes an operational amplifier and a controlling MOS transistor, which adjusts the bias current to clamp the voltage on the MOS transistor, thereby aligning the gate-source voltage and ensuring the output precisely follows the input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional source follower is used, then the circuit structure is simple and input impedance is high, but the output cannot follow the DC component of the input signal due to gate-source voltage difference
Solution Approach 1:
The patent introduces a feedback circuit comprising an operational amplifier and a controlling MOS transistor. The operational amplifier detects the difference between input and output voltages and adjusts the bias current through the controlling MOS transistor to eliminate this difference. This feedback mechanism enables the output to accurately follow the DC component of the input signal while maintaining the simplicity of the source follower structure.
Solution Approach 2:
The patent dynamically adjusts the bias current parameter supplied to the MOS transistor through the feedback circuit. By changing the bias current in response to the voltage difference between input and output, the gate-source voltage is adjusted to eliminate the DC offset, enabling precise DC component following without complex circuit reconfiguration.
2Measurement precision
If feedback circuit is added to improve DC following accuracy, then output precision is improved, but device complexity increases
Solution Approach 1:
The feedback circuit uses an operational amplifier to continuously monitor the voltage difference between input and output and automatically adjusts the bias current through the controlling MOS transistor. This closed-loop feedback mechanism achieves high output voltage accuracy by eliminating DC offset while adding minimal circuit components compared to other precision solutions.
Solution Approach 2:
The controlling MOS transistor acts as an intermediary element between the feedback circuit and the source follower. It translates the feedback signal into bias current adjustments, enabling precise control of the output voltage without directly modifying the core source follower structure, thus balancing precision and complexity.
Data Source
AI summary
A cascade complementary source follower and a controlling circuit are provided. The source follower circuit includes: a source follower circuit including at least two MOS transistors, and a feedback circuit configured to clamp a voltage on a MOS transistor that provides an output voltage in the source follower circuit and to change a gate-source voltage of the MOS transistor by adjusting a bias current supplied to the MOS transistor, so that an output voltage can precisely follow an input voltage.