Bootstrapping Circuit With Charge Injection for Faster Sampling
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Solution Overview
Problem
Conventional bootstrapping circuits for semiconductor switches face challenges in reducing current spikes during switch activation, which limits settling speed and requires significant design considerations for preceding circuitry and signal lines, especially in differential systems where common mode voltage is non-zero.
Innovation Solution
A bootstrapping circuit that includes a capacitor pre-charged while the switch is open and additional charge injection circuitry to reduce current drawn from preceding circuitry by injecting extra charge into the conductive path, allowing faster voltage settling and increased sampling speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bootstrapping is used to linearize the input signal switch, then the switch can be turned on, but a large current spike is needed which limits the settling speed and requires significant design considerations for preceding circuitry
Solution Approach 1:
The patent applies preliminary action by pre-charging the bootstrapping capacitor before the sampling phase through dedicated precharge circuitry. This ensures the capacitor is already charged to the required voltage level before the switch needs to be activated, eliminating the need for large current spikes during the critical sampling period and allowing faster settling of the input signal.
Solution Approach 2:
The patent segments the bootstrapping operation into distinct phases: a precharge phase where the capacitor is charged through precharge circuitry, and a sampling phase where the pre-charged capacitor is coupled to the switch. This segmentation allows the system to prepare the necessary charge in advance rather than demanding it all at once during switching, thereby reducing current spikes and improving settling speed.
2Reliability
If conventional bootstrapping is used, then the switch can be activated, but the capacitance seen at the input of the bootstrapper may be as big or even larger than the sample capacitance itself
Solution Approach 1:
The patent introduces precharge circuitry as an intermediary component that mediates between the power supply and the bootstrapping capacitor. This intermediary circuitry is responsible for charging the capacitor to the appropriate voltage level during a dedicated precharge phase, allowing the main bootstrapping circuit to operate with reduced capacitance demands during the sampling phase.
3Adaptability or versatility
If the buffer voltage is a common mode voltage +/- the AC part of the input signal with non-zero common mode voltage, then the buffer can operate, but it has to deliver a non-differential current to charge to the wanted voltage
Solution Approach 1:
The patent applies preliminary action by pre-charging the bootstrapping capacitor to the required voltage level (including the common mode voltage component) before the sampling operation. This preliminary charging action ensures that when the switch is activated during sampling, the buffer does not need to deliver large non-differential current spikes to charge the capacitor, thereby reducing energy consumption and allowing the buffer to operate more efficiently with differential currents.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution reduces current demand from preceding circuitry, enabling faster sampling and relaxing design specifications for buffer and signal lines, thus enhancing the sampling speed and efficiency of semiconductor switches.
Implementation Method 1
a capacitor configured to be selectively coupled to a charge source by a switch circuit of the bootstrapping circuit while the semiconductor switch is open
Implementation Method 2
additional charge injection circuitry to reduce current drawn from preceding circuitry by injecting extra charge into the conductive path
Data Source
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AI summary
A bootstrapping circuit for a semiconductor switch is provided. The bootstrapping circuit includes a capacitor, a first node for coupling to an input node of the semiconductor switch, and a second node for coupling to a control node of the semiconductor switch. Further, the bootstrapping circuit includes a switch circuit configured to selectively couple the capacitor to a charge source while the semiconductor switch is open and to selectively close a conductive path between the first node and the second node for closing the semiconductor switch. The conductive path includes the capacitor. The bootstrapping circuit additionally includes charge injection circuitry configured to inject charge into the conductive path before, while or after the conductive path is closed by the switch circuit.