Bandpass Interpolation ADC Conversion Under Sampling Jitter
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Solution Overview
Problem
Conventional analog-to-digital converters face significant precision limitations due to sampling uncertainty, particularly when processing high-frequency signals, as they struggle to maintain accuracy amidst timing jitter and frequency drift, which degrades the quality of signal conversion and is not adequately addressed by existing methods for jitter reduction and sample-rate conversion.
Innovation Solution
The implementation of a system with multiple processing branches that include digital bandpass interpolation filters and analog bandpass filters, which perform frequency decomposition and sample-rate conversion, allowing for reduced noise introduction from sampling uncertainty and enabling operation near the Nyquist limit, even with high-frequency signals, without requiring high-stability clock sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sampling/quantization circuits are used to convert high-frequency signals, then conversion speed can be achieved, but precision is degraded due to sampling uncertainty and timing jitter
Solution Approach 1:
The input signal is divided into multiple frequency bands using parallel bandpass filters, with each branch processing a specific band. This segmentation allows each sampling circuit to operate on a narrower bandwidth signal, reducing the impact of sampling jitter on high-frequency components and improving overall conversion precision.
Solution Approach 2:
A sample-rate conversion circuit is introduced as an intermediary between the sampling/quantization circuits and the output. This intermediary performs resampling and phase correction to compensate for timing jitter and frequency drift, thereby improving the precision of the final digital output without requiring ultra-stable clock sources.
2Speed
If the sampling rate is increased to process high-frequency signals near the Nyquist limit, then bandwidth is improved, but sampling uncertainty and timing jitter have a greater impact on precision
Solution Approach 1:
By segmenting the high-frequency signal into multiple parallel bands, each processed at a lower effective sampling rate, the system achieves high overall bandwidth while reducing the jitter impact on each individual band. This allows operation near the Nyquist limit without proportionally increasing sampling uncertainty effects.
Solution Approach 2:
The system measures the actual sampling instant deviations and uses this information in the sample-rate conversion circuit to correct timing errors. This feedback mechanism compensates for sampling uncertainty, allowing high sampling rates to be used without proportionally degrading precision.
3Measurement precision
If high-stability clock sources are used to reduce timing jitter, then sampling precision is improved, but device complexity and cost increase
Solution Approach 1:
Instead of relying on expensive high-stability clock sources, the patent introduces a sample-rate conversion circuit as an intermediary that actively corrects timing jitter through measurement and compensation. This approach achieves high sampling precision using standard, lower-cost clock sources by adding digital processing complexity rather than analog clock stability requirements.
Data Source
AI summary
Provided is an apparatus for converting a continuous-time, continuously variable signal into a sampled and quantized signal, which includes an input line for accepting an input signal, multiple processing branches coupled to the input line, and an adder coupled to outputs of the plurality of processing branches. Each of the processing branches includes a sampling/quantization circuit and a digital bandpass interpolation filter having an input coupled to an output of the sampling/quantization circuit. The digital bandpass interpolation filters in different ones of the processing branches have frequency responses that are centered at different frequencies. The digital bandpass interpolation filter in at least one of the processing branches includes: (i) a quadrature downconverter, (ii) a first lowpass filter and a second lowpass filter, (iii) a first interpolator and a second interpolator, each having an input for inputting a variable interpolant value, and (iv) a quadrature upconverter.