Digital Up-Converter Using CCD Filtering Without IQ Mixers
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Solution Overview
Problem
Existing digital up-converters in communications systems are complex and costly due to the use of complex circuits such as IQ mixers and oscillators, which increases the overall system cost and complexity.
Innovation Solution
A digital up-converter design utilizing a cascaded combinator-differentiator (CCD) filter, low-pass filter, up-sampler, and down-sampler, eliminating the need for complex mixers and oscillators by performing interpolation, filtering, and spectral shifting without them, using a multi-stage CCD filter and low-pass filter with a finite or infinite impulse response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex circuits such as IQ mixers and oscillators are used in digital up-converters, then signal up-conversion and spectral shifting can be achieved, but device complexity and system cost increase
Solution Approach 1:
The patent extracts and removes the complex IQ mixer and oscillator circuits from the digital up-converter architecture. Instead of using these traditional complex components, the invention employs a simplified structure based on cascaded integrator-comb (CIC) filters and digital signal processing techniques to achieve the same signal up-conversion and spectral shifting functions, thereby eliminating the source of complexity while maintaining functionality
Solution Approach 2:
The patent substitutes traditional analog/mixed-signal components (IQ mixers and oscillators) with purely digital signal processing components (CIC filters and digital processing stages). This substitution replaces complex hardware circuits with digital algorithms and structures, reducing hardware complexity, component count, and system cost while achieving equivalent or superior performance
2Manufacturing precision
If interpolation filtering is performed to increase sample rate, then spectral shaping and rejection of interpolation images is achieved, but filter complexity and number of coefficients increase
Solution Approach 1:
The patent segments the interpolation filtering process into multiple cascaded stages of integrator-comb (CI) filters. Rather than using a single complex filter with many coefficients, the invention divides the filtering function into several simpler filter stages connected in cascade, where each stage contributes to the overall spectral shaping and interpolation image rejection, thereby reducing the complexity of individual filter stages while achieving the required precision
Solution Approach 2:
The patent combines multiple CIC filter stages into a cascaded structure where the integrator and comb sections are merged and repeated across multiple stages. This merging of functions creates a powerful interpolation filter with excellent spectral shaping characteristics while keeping each individual stage relatively simple and efficient to implement
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AI summary
A digital up-converter (DUC) includes a cascaded combinator- differentiator (CCD) filter, a low-pass filter, an up-sampler, and a down-sampler. The combinator includes a number of series-connected combinator stages and the differentiator includes a number of series-connected differentiator stages. The CCD filter functions similarly to an interpolator filter, filtering and up-sampling the baseband signal out of the baseband. In one embodiment, the up-sampling factor is twice the number of channels (2N). The disclosed DUC does not require complex mixers or oscillators. Also, the low-pass filter of the DUC does not require a narrow transition band, so the number of coefficients for the low-pass filter is relatively low.