Bootstrap Sample-and-Hold Switch for Low-Resistance ADC Conversion
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Solution Overview
Problem
Analog switches in analog-to-digital converters (ADCs) have non-zero ON-resistance, leading to voltage drop and potential failure in converting analog input voltage to output voltage, especially when the input voltage exceeds a certain threshold. Additionally, external noise affects the accuracy of the digital-to-analog converter (DAC) in SAR-type ADCs.
Innovation Solution
The proposed solution involves an analog-to-digital converter with a sample and hold circuit that includes an analog switch with a bootstrap circuit to generate a boosting voltage by adding a constant voltage to the analog input voltage. This boosting voltage is used to maintain a constant gate-source voltage for the analog switch, minimizing its ON-resistance and ensuring accurate signal conversion. The converter also incorporates noise cancellation mechanisms to maintain performance in noisy environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an analog switch is used in the sample and hold circuit, then the circuit can sample and hold the analog input voltage, but the ON-resistance of the analog switch increases infinitely when the input voltage reaches a certain value, causing voltage drop and conversion failure
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the gate voltage of the analog switch transistor. By changing the gate voltage parameter from a fixed value to a dynamically controlled value that tracks the input voltage, the ON-resistance is kept constant across the entire input voltage range, resolving the contradiction between conversion reliability and ON-resistance variation.
Solution Approach 2:
The patent implements feedback by using the analog input voltage itself to control the gate voltage of the analog switch. The gate voltage is generated based on the input voltage level, creating a feedback mechanism that automatically adjusts the switch parameters to maintain constant ON-resistance, thereby eliminating the harmful resistance variation while ensuring reliable conversion.
2Measurement precision
If a conventional analog switch is used, then the circuit structure is simple, but external noise affects the output value of the DAC, reducing the accuracy of the SAR-type ADC
Solution Approach 1:
The patent introduces an intermediary mechanism by adding a controlled voltage component to the gate of the analog switch. This intermediary voltage acts as a mediator that compensates for the effects of external noise on the DAC output, thereby improving ADC accuracy without significantly complicating the overall circuit structure.
Solution Approach 2:
The patent improves measurement precision by dynamically changing the gate voltage parameter of the analog switch based on the input signal characteristics. This parameter adjustment optimizes the switch performance under different noise conditions, enhancing the overall accuracy of the SAR-type ADC while maintaining circuit simplicity.
3Ease of manufacture
If the gate voltage of the analog switch is fixed, then the circuit is simple to implement, but the ON-resistance varies with input voltage, leading to voltage drop and conversion failure
Solution Approach 1:
The patent applies self-service by enabling the analog switch to automatically adjust its own gate voltage based on the input voltage level. The switch uses the input signal itself to control its operating parameters, eliminating the need for complex external control circuits while ensuring reliable signal conversion across the full voltage range.
Solution Approach 2:
The patent resolves the contradiction between ease of manufacture and conversion reliability by implementing dynamic parameter changes in the gate voltage. This approach maintains relative circuit simplicity while significantly improving conversion reliability, as the gate voltage automatically adapts to prevent voltage drop and conversion failure.
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 minimizes the ON-resistance of the analog switch, ensuring accurate conversion of analog input voltage to output voltage across a wide range of input values. Additionally, the noise cancellation mechanism maintains high performance even in noisy environments, enhancing the overall accuracy and reliability of the ADC.
Implementation Method 1
an analog switch with a bootstrap circuit to generate a boosting voltage by adding a constant voltage to the analog input voltage
Implementation Method 2
a first capacitor in which the analog output voltage is charged
Implementation Method 3
minimizing its ON-resistance and ensuring accurate signal conversion
Data Source
AI summary
The analog-to-digital converter (ADC) includes a sample and hold circuit configured to sample an analog input voltage and hold the sampled voltage. The sample and hold circuit includes: an analog switch configured to generate a boosting voltage obtained by adding a constant voltage to the analog input voltage, and output an analog output voltage corresponding to the analog input voltage by using the boosting voltage; and a capacitor in which the analog output voltage is charged.