Bootstrapped Sampling Switch for Low-Distortion ADC Input Tracking
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Solution Overview
Problem
Sampling circuits in integrated circuits introduce distortions due to non-idealities such as variable on-resistance, channel charge depletion, sampling aperture jitter, and clock feed-through, affecting the resolution of analog to digital converter modules.
Innovation Solution
A sampling circuit with a switch and bootstrap modules that vary the control voltage with a substantially constant value to maintain a conducting channel and track input signals, using n-type or p-type MOS transistors, and capacitors to couple the control terminal with a sampling clock signal, reducing sampling distortions by maintaining constant channel charges and on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional sampling circuit uses a switch with fixed control voltage, then the circuit structure is simple, but sampling distortions occur due to variable on-resistance and channel charge depletion
Solution Approach 1:
The control voltage of the sampling switch is made dynamic by coupling it to the input signal through a bootstrap capacitor. This allows the control voltage to vary with the input signal, maintaining a substantially constant channel charge and on-resistance throughout the sampling process, thereby reducing sampling distortions while managing circuit complexity
Solution Approach 2:
The invention changes the parameter of control voltage from fixed to variable, where it now depends on the input signal. This parameter change ensures that the switch operates with constant channel charge and on-resistance, improving sampling accuracy without requiring overly complex circuit structures
2Measurement precision
If the control voltage is varied to maintain constant channel charge, then sampling distortions are reduced, but additional bootstrap circuitry increases device complexity
Solution Approach 1:
A bootstrap capacitor is introduced as an intermediary element between the input signal and the switch control terminal. This capacitor transfers the input signal voltage to the control terminal, creating the varying control voltage needed to maintain constant channel charge, thereby improving ADC resolution while keeping the added complexity manageable through a single passive component
Solution Approach 2:
The sampling switch's own control terminal is made to service itself by being coupled to the input signal. The control voltage automatically adjusts with the input signal level, eliminating the need for external complex control circuits and reducing overall device complexity while maintaining high measurement precision
3Reliability
If the switch channel charge is kept constant, then variable on-resistance distortion is minimized, but clock feed-through effects may increase
Solution Approach 1:
The control voltage parameter is changed to follow the input signal, which maintains constant channel charge and minimizes variable on-resistance distortion. The bootstrap capacitor couples the control terminal to the input signal, creating this adaptive control voltage that improves sampling consistency while managing clock feed-through effects
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 solution effectively reduces sampling distortions, enhancing the resolution of analog to digital converters by minimizing channel charge dissipation and clock feed-through, while maintaining high-speed performance.
Implementation Method 1
The first bootstrap module can include a capacitor that couples the control terminal of the switch and the node receiving the sampling clock signal
Data Source
AI summary
A sampling circuit can include a switch having a control terminal, a first channel terminal and a second channel terminal. The first channel terminal can be configured to receive an input signal, and the control terminal can be configured to have a control voltage that varies with regard to the input signal, such that a conducting channel can be formed between the first channel terminal and the second channel terminal to enable an output voltage on the second channel terminal to track the input signal. Further, the sampling circuit can include a bootstrap module coupled to the control terminal of the switch. The bootstrap module can be configured to change the control voltage by a substantially constant value to turn off the conducting channel between the first channel terminal and the second channel terminal in order to hold the output voltage as a sample of the input signal.