Harmonic-Mixing Digitizer Architecture for High-Bandwidth Sampling
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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 input signals are split and mixed with harmonic signals to digitize all frequency components effectively, allowing each ADC channel to process the entire signal bandwidth and improve the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If synchronous time-interleaving with multiple ADCs is used to achieve higher sample rate, then the effective sample rate is improved, but the system complexity and cost increase due to additional ADC circuitry and clocking circuitry
Solution Approach 1:
The input signal is divided into multiple sub-bands using filter banks, with each sub-band assigned to a separate ADC channel operating at lower sample rates. The ADCs process segments of the overall frequency spectrum simultaneously, and the results are combined through digital upconversion to reconstruct the full-bandwidth signal at the desired effective sample rate, avoiding the need for a single high-speed ADC
Solution Approach 2:
The patent transitions from time-domain interleaving to frequency-domain parallel processing by introducing filter banks that separate the input signal into multiple frequency sub-bands. This dimensional transformation allows multiple ADCs to operate independently on different frequency segments, achieving high effective sample rate through frequency diversity rather than time-domain multiplication
2Speed
If the ADC sample rate is lowered to satisfy the Nyquist sampling theorem, then the ADC can operate at lower speeds, but more ADC channels are needed to achieve the desired performance
Solution Approach 1:
The frequency spectrum is segmented into multiple sub-bands using filter banks, with each sub-band processed by a separate ADC channel. This segmentation allows each ADC to operate at a lower sample rate appropriate for its assigned bandwidth while collectively achieving the desired overall performance through parallel processing of multiple frequency segments
3Speed
If sub-bands are downconverted to a lower frequency range for digitization, then the bandwidth requirement is reduced, but the Signal-to-Noise Ratio degrades due to noise energy from all ADCs appearing in the recombined output
Solution Approach 1:
Each ADC channel is assigned to process a specific frequency sub-band with characteristics optimized for that local frequency range. The filter banks ensure that each ADC operates on signals within its optimal performance range, and the localized processing prevents noise from other channels from degrading the signal quality in each sub-band
Solution Approach 2:
The patent uses multiple ADC channels to create redundant digital representations of different sub-bands of the same input signal. By processing identical input signal energy through multiple independent ADC paths and then combining the results, the system achieves noise diversity that improves overall signal-to-noise ratio rather than degrading it
4Speed
If the number of ADC channels is increased to achieve higher sample rate, then the effective sample rate is improved, but the communication path length increases resulting in longer parasitic capacitance and electromagnetic noise
Solution Approach 1:
The system segments the high-sample-rate requirement into multiple lower-speed ADC channels, each handling a portion of the total data rate. This segmentation reduces the communication path requirements for each individual ADC, minimizing parasitic capacitance and electromagnetic noise in each channel while maintaining the overall high effective sample rate through parallel operation
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 efficient digitization of high-frequency signals across all ADC channels, reducing noise penalties and increasing the effective sample rate without the need for multiple ADC channels, thus enhancing the bandwidth and reducing system complexity.
Implementation Method 1
harmonic mixers configured to mix the split signals with harmonic signals to generate mixed signals
Data Source
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.