Source Follower Current Feedback Stabilization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The source follower circuit experiences signal distortion due to channel length modulation in NMOS transistors, and conventional solutions like current mirrors lower operational voltage, causing instability and malfunction.
Innovation Solution
A current feedback circuit is introduced, comprising a transistor, an impedance, and a comparator, which generates an error voltage and compares it with a reference voltage to adjust the drain current, stabilizing the output signal and maintaining normal operation at lower voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current mirror is added to stabilize the current, then signal distortion is prevented, but the operational voltage is lowered causing transistor malfunction
Solution Approach 1:
The patent implements a feedback mechanism where the drain current of the NMOS transistor is sensed through an impedance element, converted to a voltage signal, and fed back to the gate through a control circuit. This feedback loop automatically adjusts the gate voltage to maintain stable drain current, preventing signal distortion without requiring additional current mirror transistors that would consume excessive voltage headroom.
Solution Approach 2:
The patent replaces the conventional current mirror approach (which uses additional PMOS transistors M3 and M4) with an electronic feedback control system using an impedance element and voltage control. This substitution eliminates the need for high-voltage headroom while achieving the same current stabilization function, allowing operation at lower voltages suitable for miniaturized integrated circuits.
2Volume of moving object
If the voltage drop between source and gate of PMOS transistor is reduced for miniaturization, then circuit size is reduced, but the transistor can no longer operate normally
Solution Approach 1:
The patent employs dynamic voltage control where the gate voltage of the NMOS transistor is continuously adjusted based on the drain current feedback signal. This dynamic adjustment allows the transistor to maintain proper operating conditions even when the overall supply voltage is reduced for miniaturization, as the gate voltage adapts in real-time to compensate for voltage drops across the transistor.
Solution Approach 2:
The patent changes the operating parameters of the transistor by using feedback control to dynamically adjust the gate voltage. Instead of relying on fixed voltage margins required by conventional current mirrors, the system modifies the gate voltage parameter in response to actual current conditions, enabling reliable operation at reduced voltage levels that accommodate smaller device dimensions.
Data Source
AI summary
A current feedback circuit is used in the source follower. The source follower includes a first MOS transistor and a current mirror. The first MOS transistor has a gate receiving an inputting signal and a source outputting an output signal. A drain current flows through the first MOS transistor. The current mirror generates the drain current according to an adding current. The current feedback circuit is used for stabilizing the drain current to a constant value substantially. The current feedback circuit includes a passive component and an operational amplifier. The passive component has a first end and a second end, which has an error voltage when a corresponding current flows through the passive component. The magnitude of the corresponding current changes with the magnitude of the drain current. The operational amplifier outputs a reference signal to adjust the adding current according to the error voltage and a reference voltage.