Harmonic-Mixing Digitizer Architecture for Wider-Bandwidth Signal Capture
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Solution Overview
Problem
Conventional test and measurement instruments with asynchronous time-interleaved digitizers face limitations in bandwidth due to analog to digital converter (ADC) constraints, leading to increased complexity and noise penalties when digitizing high-frequency signals.
Innovation Solution
The implementation of harmonic mixing in ADC systems, where an input signal is split and mixed with harmonic signals to generate mixed signals that are then digitized by multiple ADCs, allowing all frequency components to be processed by each channel and improving the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If synchronous time-interleaved digitization is used to achieve higher sample rates, then the effective sample rate is improved, but the device complexity increases due to multiple ADCs and track and hold amplifiers
Solution Approach 1:
The input signal bandwidth is segmented into multiple sub-bands, with each sub-band processed by a separate ADC operating at a lower sample rate. This segmentation allows the system to achieve high effective bandwidth without requiring high-speed ADCs, thereby reducing complexity while maintaining performance
Solution Approach 2:
The patent changes the frequency parameter of the input signal by downconverting different sub-bands to baseband or lower intermediate frequencies. This parameter transformation enables standard low-speed ADCs to process high-frequency content, resolving the contradiction between sample rate requirements and ADC capabilities
2Speed
If sub-bands are downconverted to lower frequency ranges for digitization, then the ADC sample rate requirement is reduced, but the signal-to-noise ratio deteriorates due to noise accumulation from multiple ADCs
Solution Approach 1:
The patent introduces digital signal processing as an intermediary stage that coherently combines the outputs from multiple ADCs. This digital combining process properly weights and phases the individual ADC outputs, preventing noise accumulation and maintaining signal-to-noise ratio while enabling the use of multiple lower-speed ADCs
3Productivity
If the number of ADC channels is increased to achieve desired performance, then the sample rate capability is improved, but the cost and complexity increase due to additional circuitry and longer communication paths
Solution Approach 1:
The patent designs a universal processing architecture where each ADC channel processes a specific frequency sub-band, and all channels share common control and processing resources. This multi-functional approach allows the system to achieve high effective bandwidth through frequency division rather than requiring all channels to operate at maximum speed, reducing overall chip complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables effective digitization of high-frequency signals across all ADC channels, reducing noise penalties and increasing the usable bandwidth without the need for multiple high-bandwidth ADC channels, thereby simplifying the system and improving signal quality.
Implementation Method 1
harmonic mixing for reducing noise... an input signal is split and mixed with harmonic signals to generate mixed signals that are then digitized by multiple ADCs
Data Source
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AI summary
A test and measurement instrument including a splitter configured to split an input signal having a particular bandwidth into a plurality of split signals, each split signal including substantially the entire bandwidth of the input signal; a plurality of harmonic mixers, each harmonic mixer configured to mix an associated split signal of the plurality of split signals with an associated harmonic signal to generate an associated mixed signal; and a plurality of digitizers, each digitizer configured to digitize a mixed signal of an associated harmonic mixer of the plurality of harmonic mixers. A first-order harmonic of at least one harmonic signal associated with the harmonic mixers is different from an effective sample rate of at least one of the digitizers.