Digital Sample Rate Conversion Using Nonlinear Interpolation
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Solution Overview
Problem
Existing sample rate converters face challenges in accurately converting discrete-time signals between different sampling frequencies, leading to signal-to-noise ratio (SNR) issues due to the inability to accurately model non-linear functions present in continuous-time filters.
Innovation Solution
A digital sample rate converter that uses a non-linear interpolation filter to simulate a mixed signal SRC system model, incorporating a discrete-time filter and interpolator to generate interpolated sample values between adjacent samples, effectively modeling a continuous-time low pass filter response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a digital-to-analog converter and analog low pass filter are used to convert discrete-time signals, then the system can interface between different sampling frequencies, but the signal-to-noise ratio deteriorates due to inability to accurately model non-linear functions
Solution Approach 1:
The patent replaces the mixed signal approach (digital-to-analog converter plus analog filter) with a fully digital signal processing system. The digital non-linear interpolation filter substitutes for the analog low pass filter, eliminating the need for digital-to-analog conversion and subsequent analog filtering, thereby maintaining signal integrity and improving signal-to-noise ratio while achieving sample rate conversion between different sampling frequencies
Solution Approach 2:
The patent changes the fundamental parameter of signal representation from analog continuous-time to digital discrete-time throughout the entire processing chain. By using digital non-linear interpolation to model the continuous-time filter response, the system maintains precision in the digital domain, avoiding the signal-to-noise ratio degradation that occurs when converting to and from analog domains
2Device complexity
If linear interpolation is used in sample rate conversion, then the device complexity is reduced, but the accuracy of modeling continuous-time filter response deteriorates
Solution Approach 1:
The patent employs non-linear interpolation that dynamically adapts to the signal characteristics and sampling frequency ratio. The interpolation filter adjusts its behavior based on the specific conversion requirements, using non-linear processing to accurately model the continuous-time filter response while managing complexity through efficient digital implementation strategies
Data Source
AI summary
A signal processing system includes a digital sample rate converter to convert a signal sampled at a first sampling frequency into a corresponding signal sampled at a second sampling frequency. In at least one embodiment, the sample rate converter includes a digital sample rate conversion filter. The digital sample rate conversion filter includes a digital filter that models a continuous time filter such as a low pass RC filter and generates filtered samples. The digital sample rate conversion filter also includes an interpolation filter that determines samples between the digital filtered samples. A sample selector selects the samples generated by the interpolation filter at the second sampling frequency. In at least one embodiment, the sample selector determines when to generate interpolated samples and the amount of time offset from an adjacent sample generated by the digital filter.