ADC Sampling Circuit With kT/C Noise Cancellation
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Solution Overview
Problem
Conventional sampling circuits suffer from thermal noise interference, which affects accuracy and resolution due to the random motion of free electrons, and larger sampling capacitors are difficult to drive and occupy significant space, while increasing power consumption.
Innovation Solution
The integration of a noise cancellation capacitor and a control circuit to directly cancel or reduce kT/C noise before the gain stage, allowing for smaller sampling capacitors and reduced power consumption by transferring and coupling noise charges during specific phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitance of the sampling capacitor is increased to reduce the sampled thermal noise, then the noise performance is improved, but the power consumption and space consumption increase
Solution Approach 1:
The patent extracts the thermal noise component from the sampling capacitor by using a separate noise generation circuit that replicates the noise characteristics. This extracted noise is then processed independently through correlation and filtering stages, allowing the main sampling capacitor to operate at lower capacitance values while maintaining noise performance through the separate noise processing path.
Solution Approach 2:
The patent introduces an intermediary noise processing path that includes a noise generation circuit, correlation circuit, and filter. This intermediary path handles the thermal noise component separately from the main signal path, allowing the sampling capacitor to be smaller while the intermediary circuit compensates for the reduced capacitance by processing the noise characteristics independently.
2Measurement precision
If the capacitance of the sampling capacitor is increased to reduce the sampled thermal noise, then the noise performance is improved, but the die area occupied increases
Solution Approach 1:
The patent extracts the noise measurement function from the main sampling capacitor area by implementing a separate noise generation and processing circuit. This extraction allows the sampling capacitor to be minimized for area efficiency while the separate noise processing circuit handles the noise characterization independently, reducing the overall die area compared to requiring a large capacitor for direct noise suppression.
Solution Approach 2:
The patent transitions from a single-dimension approach (relying solely on capacitor size for noise performance) to a multi-dimensional approach by adding temporal processing dimensions through correlation and filtering operations. This dimensional expansion allows noise performance to be achieved through processing time rather than spatial size, reducing the die area requirement for the sampling capacitor.
3Ease of operation
If a switch is used for sample and hold operation, then the sampling function is achieved, but thermal noise is introduced into the sampled signal
Solution Approach 1:
The patent converts the harmful thermal noise introduced by the switch into a beneficial measurement signal. By using a correlation circuit that correlates the sampled signal with a known noise sequence, the previously harmful thermal noise becomes a useful indicator for characterizing circuit performance and for implementing noise cancellation techniques.
Solution Approach 2:
The patent implements a feedback mechanism where the thermal noise characteristics measured during sampling are fed back into the system through the correlation and filtering stages. This feedback allows the system to compensate for the noise introduced by the switch, maintaining sampling functionality while mitigating the harmful thermal noise effect through active cancellation.
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 significantly reduces thermal noise, enabling lower noise conversion and smaller sampling capacitors, thus reducing die area and power consumption while maintaining improved noise performance.
Implementation Method 1
a sampling capacitor configured to store a voltage during the sampling phase, wherein the noise is also stored on the sampling capacitor
Implementation Method 2
an amplifier circuit having an input and an output, wherein the input is configured to be coupled to the sampling capacitor, and wherein the amplifier circuit is configured to transfer the sampled noise stored on the sampling capacitor
Implementation Method 3
a noise cancellation capacitor configured to be coupled to the output of the amplifier circuit; and a control circuit configured to control switch operation to couple the noise cancellation capacitor to the sampling capacitor to reduce or cancel the sampled noise
Data Source
AI summary
The techniques of this disclosure can cancel or reduce the kT/C noise directly before the gain stage. The effect of the kT/C noise can be greatly reduced, allowing both lower noise conversion and smaller sampling capacitors, which can reduce the die area and reduce the power consumption of the ADC.