Spectral Stitching for Wider VSG Bandwidth Without Dynamic Range Loss

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Solution Overview

Problem

Current methods for increasing instantaneous bandwidth in RF vector signal analyzers and generators, such as time-interleaving and quadrature mixing, face limitations including inaccuracies, scalability issues, and image rejection problems, which hinder achieving larger bandwidths without sacrificing dynamic range.

Innovation Solution

The spectral stitching method processes digital signals using multiple parallel processing paths, each handling a frequency band with a specific center frequency and overlap region, phase-locked and time-synchronized, to combine these bands into an aggregate frequency band, utilizing frequency-shifting, filtering, and gain/phase adjustments to achieve higher bandwidths without the drawbacks of existing methods.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If time-interleaving is used to increase bandwidth, then instantaneous bandwidth is improved, but measurement precision and reliability deteriorate due to time alignment inaccuracies and magnitude/phase differences between ADCs

Engineering Contradiction:

Improveinstantaneous bandwidthVSAvoiddynamic range

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The aggregate frequency band is divided into multiple overlapping frequency bands, each processed by a separate parallel processing path. Each path handles a specific frequency band with its own center frequency, allowing independent optimization while maintaining overall system performance through the overlapping regions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Overlapping frequency bands serve as intermediary regions between adjacent bands. These overlap regions contain calibration tones that act as mediators for determining complex calibration constants, which correct phase and magnitude differences between processing paths without requiring precise time alignment.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If quadrature mixing is used to increase bandwidth, then instantaneous bandwidth is improved, but harmful factors are generated including DC leakage spurs and image spurs

Engineering Contradiction:

Improveinstantaneous bandwidthVSAvoidDC leakage spur and image spur

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The frequency band is segmented into multiple overlapping bands processed in parallel, avoiding the single-band quadrature mixing approach that generates DC leakage and image spurs. Each segment is processed independently with its own frequency shifts, preventing the generation of harmful spurs.

Inventive Principle:

Principle #1Segmentation

3Speed

If quadrature mixing is used to increase bandwidth, then instantaneous bandwidth is improved, but adaptability is limited as the method only scales to two converters

Engineering Contradiction:

Improveinstantaneous bandwidthVSAvoidscalability

Core Design Contradiction:

SpeedVSAdaptability or versatility

Solution Approach 1:

The system segments the frequency band into N overlapping bands, each handled by a separate processing path. This segmentation allows the system to scale to any number of converters N, unlike quadrature mixing which is limited to two converters. Each segment can be independently configured and calibrated.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The parallel processing path architecture is universal and can be applied to any number of converters N. The same calibration and combining methodology works for 2 converters, 3 converters, or any arbitrary number, making the system highly adaptable and versatile for different bandwidth requirements.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Speed

If time-interleaving is used to increase bandwidth, then instantaneous bandwidth is improved, but device complexity increases due to the need for DSP correction algorithms

Engineering Contradiction:

Improveinstantaneous bandwidthVSAvoidDSP correction algorithms

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

Complex calibration constants are determined in advance during a calibration phase using overlap region calibration tones. These pre-determined calibration constants are then stored and applied during normal operation, eliminating the need for complex real-time DSP correction algorithms and reducing operational device complexity.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9609653B2Spectral stitching method to increase instantaneous bandwidth in vector signal generators

Publication Date: 2017.03.28 NATIONAL INSTRUMENTS CORP

AI summary

Embodiments are described of devices and methods for processing a signal using a plurality of vector signal generators (VSGs). A digital signal may be provided to a plurality of signal paths, each of which may process a respective frequency band of the signal, the respective frequency bands having regions of overlap. The gain and phase of each signal path may be adjusted such that continuity of phase and magnitude are preserved through the regions of overlap. The adjustment of gain and phase may be accomplished by a complex multiply with a complex calibration constant. The calibration constant may be determined for each signal path by comparing the gain and phase of one or more calibration tones generated within each region of overlap. Each signal path may comprise a VSG to convert the respective signal to an analog signal, which may be combined to obtain a composite signal.