Bootstrapped Switch Gate Protection for Fast Turn-Off
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Solution Overview
Problem
Bootstrapped switches experience slow turn-off times due to the voltage at the gate being beyond the supply rails, leading to reduced 'on' time and signal-dependent errors, particularly in high-speed applications.
Innovation Solution
A protection device is coupled to the bootstrapped switch, controlled by an input voltage during the boosting phase and a constant voltage during the non-boosting phase, to improve turn-off times by minimizing the impact of parasitic capacitance and signal dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate voltage is boosted beyond the supply rails to maintain constant gate-to-source voltage, then the switch resistance becomes independent of input signal and parasitic capacitances are reduced, but the turn-off time increases significantly
Solution Approach 1:
The gate control is segmented into two independent paths: a bootstrapped path for the on-state (providing constant gate-to-source voltage) and a separate turn-off path that actively discharges the gate. This segmentation allows the bootstrapped switch to maintain its benefits while eliminating the slow turn-off problem by providing a dedicated discharge mechanism independent of the input signal.
Solution Approach 2:
The turn-off circuit is prepared in advance with a discharge path that is activated when turn-off is needed. By having the gate connected to ground through the turn-off circuit during the on-state (but isolated by the switch), the discharge path is pre-established, enabling rapid turn-off when the switch is turned off, rather than waiting for natural discharge through parasitic capacitances.
2Productivity
If the gate voltage remains high during the on-state, then the switch maintains low resistance, but the turn-off becomes signal-dependent leading to distortion errors
Solution Approach 1:
The turn-off circuit acts as an intermediary element between the bootstrapped gate and ground. It provides a controlled discharge path that is mediated by the switch state, allowing the gate to be rapidly discharged to ground through the turn-off circuit when the switch is off, independent of the input signal level. This eliminates signal-dependent turn-off variations and associated distortion.
Data Source
AI summary
The present disclosure provides designs and techniques to improve turn “off” times of a bootstrapped switch, maximizing the total “on” time of the bootstrapped switch. The techniques described herein provide a protection device coupled to the bootstrapped switch. The protection device may be controlled by an input voltage to the bootstrapped switch during a boosting phase and may be controlled by a constant voltage during a non-boosting phase. The techniques for reducing turn “off” times are particularly useful in high-speed applications, such as high-speed, low-voltage analog-to-digital converters.