Analog Switch Gate-Boost Circuit for Fast Turn-On and Flat On-Resistance
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Solution Overview
Problem
Analog signal switches face challenges in reducing turn-on time and enhancing 'on' resistance flatness, leading to errors in signal chains, particularly in commercial HVAC systems where multiple inputs are multiplexed.
Innovation Solution
The proposed analog switch design includes a current source that supplies a boost gate current during a boost period and a reduced gate current thereafter, along with a clamp circuit and Vgs detection circuit to bias the switch, reducing turn-on time and enhancing on-resistance flatness without requiring a charge pump, thus reducing die area and improving signal processing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a charge pump is used to provide boost gate current for fast turn on, then the turn-on time is reduced, but the die area increases and device complexity increases
Solution Approach 1:
The patent extracts the charge pump function from the analog switch circuit by implementing a separate boost circuit that provides gate boost current only when needed during turn-on. This separation eliminates the need for a dedicated charge pump component while achieving fast turn-on performance, thereby reducing die area and device complexity.
Solution Approach 2:
The boost circuit is designed to provide gate boost current in advance during the turn-on transition before the switch fully conducts. The circuit detects the turn-on state and preemptively supplies the necessary gate current to accelerate the switching action, reducing turn-on time without requiring continuous high current capability.
2Loss of time
If a charge pump is used to provide boost gate current for fast turn on, then the turn-on time is reduced, but the die area increases
Solution Approach 1:
The patent removes the charge pump component from the circuit and replaces it with a compact boost circuit implementation that achieves the same fast turn-on effect using available circuit nodes and transistors, thereby minimizing die area consumption while maintaining performance.
Solution Approach 2:
The boost circuit is designed to serve multiple functions: providing gate boost current for fast turn-on, detecting switch state through the clamp circuit, and automatically regulating current delivery. This multi-functionality eliminates the need for separate dedicated components, reducing overall die area.
3Device complexity
If conventional biasing is used without clamp circuit, then device complexity is reduced, but on-resistance flatness deteriorates and errors increase
Solution Approach 1:
The clamp circuit acts as an intermediary element that mediates between the gate and source terminals to maintain precise voltage control. By clamping the voltage differential and providing a reference node, it enables accurate biasing that ensures flat on-resistance characteristics across the switch's operating range, reducing signal chain errors.
4Speed
If boost gate current is continuously supplied, then turn-on speed is maintained, but energy consumption increases
Solution Approach 1:
The boost circuit operates periodically rather than continuously, activating only during the turn-on transition when fast switching is required. The circuit detects the turn-on state and provides gate boost current only during this brief period, then transitions to a low-power state, thereby maintaining turn-on speed while minimizing energy consumption during steady-state operation.
Data Source
AI summary
An analog switch includes an input terminal, an output terminal, a common gate, and a common source. The switch includes a current source which has a first input coupled to a first voltage supply, a control input coupled to receive a gate boost signal, and an output coupled to the common gate. The current source supplies a boost gate current to the common gate during a boost period and supplies a reduced gate current during a second period different than the boost period. The switch includes a clamp circuit which has a first terminal coupled to the common gate, a second terminal coupled to the common source, and a third terminal. The switch includes a Vgs detection circuit which provides the gate boost signal responsive to a conduction of current through the clamp circuit.