Bandpass Interpolation Filters for Jitter-Resistant Signal Quantization
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Solution Overview
Problem
Conventional data converters face significant performance degradation due to sampling jitter, particularly at high sampling rates, and existing methods for jitter attenuation and sample-rate conversion are inadequate for high-frequency input signals, leading to reduced accuracy and increased noise in the conversion process.
Innovation Solution
The implementation of a system with first and second interpolation filters coupled to the output of low-pass filters, applying phase rotation based on a variable interpolant value to complex-valued data samples, which reduces output noise and makes converter circuits less sensitive to sampling uncertainty, enabling effective operation near the Nyquist limit and mitigating both high-frequency and low-frequency jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional sampling/quantization circuits operate at high sampling rates near the Nyquist limit, then conversion speed and bandwidth are improved, but sampling jitter causes increased output noise and reduced accuracy
Solution Approach 1:
A digital filter is introduced as an intermediary component between the sampling/quantization circuit and the output. This filter receives the quantized samples and reconstructs the continuous-time signal, effectively mediating the transition from discrete to continuous domain while reducing the impact of sampling jitter on the final output accuracy
Solution Approach 2:
The patent replaces reliance on high-stability mechanical/resonant clock sources with a digital signal processing approach. Instead of depending on precise physical oscillators, the system uses digital filtering and interpolation to correct for timing variations, substituting electronic/digital methods for mechanical precision requirements
2Measurement precision
If high-stability clock sources with resonators are used to reduce sampling jitter, then conversion accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex mechanical resonator-based clock sources with simpler digital electronics. The high-stability resonator circuits are substituted with digital filters and processing algorithms that achieve comparable or superior jitter mitigation without the complexity of precision mechanical oscillators
Solution Approach 2:
Instead of using expensive high-stability clock sources, the patent creates a digital copy or model of the desired signal behavior through filtering and interpolation. The digital filter reconstructs the ideal signal waveform from imperfect samples, effectively copying the intended signal characteristics without requiring perfect timing hardware
3Reliability
If conventional jitter attenuation methods are applied, then sampling uncertainty is reduced, but the methods are inadequate for high-frequency input signals and do not enable operation near the Nyquist limit
Solution Approach 1:
The patent implements a dynamic digital filter that can adapt to different sampling rates and signal frequencies. The filter characteristics are optimized for the specific operating conditions, allowing the system to maintain effective jitter attenuation across a wide range of frequencies including operation near the Nyquist limit
Solution Approach 2:
The patent changes the approach from attenuating jitter in the time domain to filtering in the frequency domain. By transforming the problem into frequency domain processing through digital filtering, the system can effectively handle high-frequency signals and operate near the Nyquist limit where conventional time-domain jitter attenuation fails
Data Source
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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.