Comparator Input Load Compensation for Kickback Noise Reduction
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Solution Overview
Problem
Comparators in analog-to-digital converters face challenges due to variations in input load on the reference signal, leading to kickback noise and data conversion errors, particularly in multi-signal conversions where cross-talk can occur, and existing solutions like feedback control loops have limitations such as stability issues and restricted comparator design.
Innovation Solution
A comparator device with a compensating mechanism that includes a controlling device to sense operational parameters of the input load and adjust a third input device to maintain a constant total input load, independent of the comparator circuit's operation, using CMOS transistors to mirror currents and maintain constant drain current, thus eliminating kickback noise without feedback loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a feedback control loop is used to minimize input load variation, then kickback noise is reduced, but the solution introduces stability issues and oscillations
Solution Approach 1:
The patent introduces a dummy transistor connected to the reference signal input that acts as an intermediary element. This dummy transistor mirrors the bias current of the first input transistor and provides a compensating input load variation that cancels out the kickback noise generated by the first input transistor, eliminating the need for a feedback control loop and its associated stability issues
Solution Approach 2:
The patent changes the parameter of input load by dynamically adjusting the bias current of the dummy transistor to match the bias current of the first input transistor. This parameter matching ensures that the input load variations are equal and opposite, thereby canceling each other out and minimizing kickback noise without requiring feedback control
2Object-affected harmful factors
If feedback control loop changes bias current through input transistor, then input load variation is minimized, but comparator bandwidth changes which is undesirable
Solution Approach 1:
The patent segments the input stage into two separate transistors: the first input transistor that receives the reference signal and the dummy transistor that provides compensation. This segmentation allows the bias current to be distributed between the two transistors, maintaining constant total input load while preserving the comparator bandwidth by preventing large current changes through the signal path transistor
3Object-affected harmful factors
If feedback control loop is implemented, then kickback noise is reduced, but the design freedom for sizing input transistor is limited
Solution Approach 1:
The patent creates a copy of the first input transistor in the form of a dummy transistor with identical characteristics. This copy is connected to the reference signal input and biased to match the first transistor's bias current, providing a duplicate input load variation that cancels the kickback noise. This copying approach eliminates the need for complex feedback control and restores full design freedom for sizing the input transistor
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 solution effectively minimizes input load variations, reduces kickback noise, and allows for flexible comparator design optimization, improving data converter performance and linearity across various signal conditions without stability issues.
Implementation Method 1
This disturbance of reference signal is sometimes named kickback noise. The impact of the operation of the comparator on the input reference signal is of high importance and this impact should be reduced as much as possible.
Implementation Method 2
a third input device (9) connected to the first input terminal (1) for receiving the reference signal, wherein the third input device is essentially identical to the first input device (3), wherein the third input device (9) is operable for generating a second variation of an input load to the reference signal
Data Source
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AI summary
The present disclosure relates a comparator device for comparing an analog signal with a reference signal, the comparator device comprising a first input terminal for receiving a reference signal, a second input terminal for receiving an analog signal, a comparator circuit for comparing the analog signal with the reference signal and a compensating device. The comparator circuit comprises a first input device for receiving the reference signal and the compensating device comprises a third input device and a controlling device. The controlling device is configured for sensing a parameter at the first input device, and wherein a variation of the parameter is indicative of a first variation of an input load to the reference signal. The third input device is configured for receiving the reference signal and operable for generating a second variation of the input load to the reference signal. The controlling device is configured for controlling the third input device such that any first variation of the input load through the first input device is cancelled out by a complementary second variation of the input load through the third input device.