Bootstrapped Switching Circuit with Decoupled Fast Turn-On Loop
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Solution Overview
Problem
Existing bootstrapped switching circuits have limitations in achieving fast turn-on times due to the large capacitive load and voltage requirements, which affect their performance in applications like analog-to-digital converters and sampling circuits.
Innovation Solution
The implementation of an inner switching loop that decouples the bootstrapped drive circuit output from the input switch, using smaller capacitance devices and low-threshold devices to enable faster turn-on, along with the option of a buffer or pass gate to further enhance turn-on speed without compromising linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a traditional bootstrapped drive circuit is used to drive the gate of a MOSFET switch, then the circuit can provide sufficient voltage to keep the switch on, but the turn-on time is slow due to large capacitive load
Solution Approach 1:
The patent divides the bootstrapped drive circuit into two separate circuits: an inner switching loop and an outer bootstrapped drive circuit. The inner loop handles the fast switching function with minimal capacitance, while the outer circuit provides the voltage boosting function. This segmentation allows the turn-on process to be decoupled from the large capacitive load of the boot capacitor, enabling faster switching speeds.
Solution Approach 2:
The patent introduces an intermediate switching loop circuit that acts as a mediator between the input signal and the bootstrapped drive circuit. This intermediate loop contains a smaller capacitor (first capacitor) that charges and discharges rapidly to drive the input switch, while the outer bootstrapped circuit (with larger boot capacitor) provides the voltage level shifting function. The intermediary loop isolates the fast switching requirements from the voltage boosting requirements.
2Speed
If the bootstrapped drive circuit output is directly coupled to the input switch, then the circuit structure is simple, but the turn-on speed is limited by the voltage requirements and capacitive load
Solution Approach 1:
The patent segments the drive circuit into two functional blocks: the inner switching loop (comprising input switch, first capacitor, and associated transistors) and the outer bootstrapped drive circuit (comprising output switch, boot capacitor, and associated transistors). This segmentation creates an intermediate switching loop that handles fast switching while the outer circuit handles voltage boosting, achieving fast turn-on without excessive complexity.
3Quantity of substance
If larger capacitance devices are used in the bootstrapped drive circuit, then the voltage storage capability is improved, but the turn-on time increases
Solution Approach 1:
The patent separates the voltage storage function (handled by the boot capacitor in the outer circuit) from the switching function (handled by the first capacitor in the inner loop). The first capacitor has small capacitance optimized for fast charging/discharging, while the boot capacitor has large capacitance optimized for voltage storage. This segmentation allows each capacitor to be optimized for its specific function without compromise.
Solution Approach 2:
The inner switching loop performs preliminary switching action by rapidly charging and discharging the first capacitor to turn on the input switch before the outer bootstrapped circuit completes its voltage charging cycle. This preliminary action enables fast turn-on independent of the slower voltage charging process of the boot capacitor.
Data Source
AI summary
An apparatus and method for implementing a bootstrapped switching circuit (100) having improved (i.e. faster) turn-on time is provided. In an embodiment, an inner switching loop (mn1x, CBOOTX, mp0x) is implemented in a bootstrapped switching circuit where the inner switching loop is configured to turn on an input switch (mn1, mn1x) in the bootstrapped drive circuit independent of the drive circuit output (qbtstrp). The embodiment decouples the inner switching loop circuitry from the output drive circuit of the bootstrapped switching circuit (mn1, CBOOT, MP0), which typically has a larger load capacitance than the inner switching loop. This allows the inner switching loop to turn on the input switch in the bootstrapped switching circuit faster and decreases the turn-on time of the bootstrapped switching circuit.