ADC Input Charge Path Bypassing RC Filter Noise Limits
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Solution Overview
Problem
Analog-to-digital converters (ADCs) face challenges in achieving quick operation while minimizing noise and power dissipation due to non-linear parasitic capacitances, which require a broader bandwidth RC filter, increasing noise and power consumption.
Innovation Solution
A separate input node is provided to charge parasitic capacitances directly, bypassing the input RC filter, allowing for a lower bandwidth filter and reduced power dissipation, and operational amplifiers with high input impedance can be used to supply charge without disturbing the filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a broader bandwidth RC filter is employed to allow charge to pass quickly to parasitic capacitances, then settling time is reduced, but noise and power dissipation increase
Solution Approach 1:
The patent segments the charge supply path by providing a separate auxiliary input specifically for charging parasitic capacitances, distinct from the main signal input path through the RC filter. This allows independent optimization of signal filtering and capacitance charging functions.
Solution Approach 2:
The patent extracts the charge supply function for parasitic capacitances from the main signal path. By taking out this specific function and providing it through a separate auxiliary input, the main RC filter can be optimized for noise reduction without compromising settling time.
2Loss of time
If a broader bandwidth RC filter is employed to allow charge to pass quickly to parasitic capacitances, then settling time is reduced, but sampled noise increases
Solution Approach 1:
The patent segments the charge supply path by providing a separate auxiliary input specifically for charging parasitic capacitances, distinct from the main signal input path through the RC filter. This allows independent optimization of signal filtering and capacitance charging functions.
Solution Approach 2:
The patent extracts the charge supply function for parasitic capacitances from the main signal path. By taking out this specific function and providing it through a separate auxiliary input, the main RC filter can be optimized for noise reduction without compromising settling time.
3Loss of energy
If a larger resistor value is used in the RC filter, then power dissipation is reduced, but settling time increases
Solution Approach 1:
The patent segments the charge supply path by providing a separate auxiliary input specifically for charging parasitic capacitances, distinct from the main signal input path through the RC filter. This allows independent optimization of signal filtering and capacitance charging functions.
Solution Approach 2:
The patent extracts the charge supply function for parasitic capacitances from the main signal path. By taking out this specific function and providing it through a separate auxiliary input, the main RC filter can be optimized for noise reduction without compromising settling time.
Data Source
AI summary
Input stages for an analog to digital converter wherein charge for charging parasitic capacitances in the input stage, and particularly in the input switch is sourced from a node which means that it does not have to pass through the input RC filter. This has the effect that the input RC filter can be of lower bandwidth, and/or have a larger resistor value, with the consequent result that there is lower power dissipation in the ADC drive circuitry. In one example this effect is realized by providing a separate input into which charge to charge the parasitic capacitances can be fed from external circuitry. In another example an operational amplifier having high (ideally infinite) input impedance can be used to feed charge to the input switch from the input to the RC filter, or from the node between the resistor and capacitor of the filter, again without unsettling the filter.