TI ADC Sampling Capacitance Randomization for Bandwidth Mismatch
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Solution Overview
Problem
Time interleaved (TI) analog-to-digital converters (ADC) suffer from bandwidth mismatch due to variations in resistance and capacitance of the paths connecting the input terminal to the samplers, leading to spurious tones that degrade the output signal integrity.
Innovation Solution
The technique involves modifying the phase oscillation of the input signal by controlling the sampling capacitors to introduce additional phase shifts, increasing the periodicity of the phase oscillation, and varying the capacitance in a randomized or pseudo-random manner to spread the energy of spurious tones across the frequency spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If time interleaved ADC uses multiple ADC units with fixed sampling capacitance, then high sampling rate is achieved, but bandwidth mismatch causes spurious tones that degrade signal integrity
Solution Approach 1:
The patent applies dynamics by making the sampling capacitance variable rather than fixed. Each ADC unit's sampling capacitance is dynamically adjusted based on a random or pseudo-random sequence, allowing the system to adapt its electrical characteristics to mitigate bandwidth mismatch while maintaining high sampling rates through time-interleaved operation
Solution Approach 2:
The patent changes the electrical parameters (capacitance values) of the sampling capacitors in each ADC unit. By varying the capacitance parameters according to randomized sequences, the system alters the bandwidth characteristics of each path to reduce phase oscillations and eliminate spurious tones, thereby improving signal integrity
2Reliability
If sampling capacitance is randomized to spread spurious tone energy, then SFDR is improved, but device complexity increases due to additional control circuitry
Solution Approach 1:
The patent segments the capacitance control into independent randomization sequences for each ADC unit. Rather than requiring a complex centralized control system, each ADC unit has its own simplified capacitance control circuit that operates independently according to a predetermined random or pseudo-random sequence, reducing overall system complexity
Data Source
Figure 1A~1B
Figure 1C
Figure 1D
AI summary
Described herein are techniques for mitigating bandwidth mismatch in time-interleaved (TI) analog-to-digital converters (ADC). The techniques described herein involve spreading the energy associated with spurious tones resulting from bandwidth mismatch across the frequency spectrum, thereby reducing the overall impact of each individual tone. In some embodiments, for example, the tones may disappear under the noise floor. Spreading the energy associated with the spurious tones can be achieved by increasing the periodicity of the phase oscillation. This, in turn, can be achieved by introducing, in the phase oscillation, artificial phase shifts in addition to the phase shifts arising due to bandwidth mismatch. In one example, increasing the periodicity of a phase oscillation from 4 phase samples to 8 phase samples can result in a reduction in the power of a tone as high as 7 dB.