Buffered SAR ADC Front End for Repressed Input Current
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Solution Overview
Problem
Capacitive SAR ADCs are susceptible to non-linearity due to switch operations, leading to signal-dependent current variations that affect performance and increase costs.
Innovation Solution
Incorporating an amplifier as a buffer between the first switch and the input node, and controlling switches with a predetermined timing to isolate the input node from switching operations, using larger impedance switches to reduce non-linear components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If switches are operated to convert analog signal to digital signal in capacitive ADC, then ADC conversion function is achieved, but non-linearity and signal-dependent current variations occur affecting performance
Solution Approach 1:
An amplifier is introduced as an intermediary component between the switch and the input node. The amplifier buffers the switch operations, isolating the input node from direct switch effects. This mediator absorbs the harmful switching transients while maintaining accurate signal transfer, thereby reducing non-linearity and current variations without compromising conversion accuracy.
Solution Approach 2:
The ADC input circuit is segmented into distinct functional blocks: the input node, the amplifier buffer stage, and the switch network. By separating the switching operations from the input node through the amplifier, each component can be optimized independently - the switch for speed and the amplifier for linearity, thus resolving the performance contradiction.
2Reliability
If buffer amplifier and additional switches are added to isolate input node from switching operations, then non-linearity is reduced, but device complexity increases
Solution Approach 1:
The amplifier is designed to serve multiple functions simultaneously: it acts as a buffer to isolate the input node, provides gain to drive the subsequent stages, and functions as an active shield against switching noise. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in circuit complexity while improving reliability.
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
This approach reduces non-linearity and noise in the ADC output, ensuring accurate and reliable digital signal conversion with a cost-effective design.
Implementation Method 1
a capacitor coupled to an output of the amplifier via a first switch and coupled to an input of an analog-to-digital converter (ADC) via a second switch
Data Source
AI summary
A system includes an amplifier to receive a signal, an analog-to-digital converter (ADC), a first switch coupled to a capacitor to receive an output from the amplifier, the capacitor to provide the output to the ADC, a second switch coupled between the capacitor and the ADC to turn on/off the ADC, a third switch coupled between the amplifier and the first switch to connect/disconnect the output to/from the first switch, a fourth switch coupled between the amplifier and the first switch to bypass the amplifier, and circuitry. The circuitry turns on the first switch and the second switch to initiate charging the capacitor, turns on the fourth switch and turns off the third switch to complete the charging, and turns off the second switch and the first switch to control the ADC to convert the output to a digital signal.