Multiband Overlay Mixer for Wideband Signal Digitization
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Solution Overview
Problem
Current test and measurement instruments, such as digital oscilloscopes, are limited by the input bandwidth of their acquisition systems, requiring costly and time-consuming development of sophisticated track and hold sampling circuitry and analog-to-digital conversion. There is a need for a multi-band overlay mixer apparatus that allows for arbitrary mixer local oscillator coefficients and efficient reconstruction of wide band input signals using narrower bandwidth digitizers.
Innovation Solution
A multi-band overlay mixer apparatus that splits wide band RF input signals into multiple paths, frequency shifts them to lower bandwidths using oscillators with arbitrary coefficients, and reconstructs the original signal using a reconstruction section with digitizers, enabling simultaneous digitization of two wide band signals with four narrower bandwidth digitizers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sophisticated track and hold sampling circuitry and analog-to-digital conversion circuitry are used to achieve high frequency signal acquisition, then measurement precision is improved, but device complexity and capital investment increase
Solution Approach 1:
The input signal is divided into multiple frequency sub-bands using bandpass filters. Each sub-band is then processed by a separate mixer with its own local oscillator, allowing the system to handle wide bandwidth signals using multiple narrower bandwidth processing paths rather than requiring a single high-bandwidth acquisition path.
Solution Approach 2:
Mixers with local oscillators are introduced as intermediary components to frequency shift each sub-band signal to a lower baseband frequency range. This allows standard lower-bandwidth digitizers to process signals that originally exceeded their bandwidth capabilities, resolving the contradiction between measurement precision and device complexity.
2Adaptability or versatility
If mixer technology is used to frequency shift sub-bands to baseband, then input bandwidth is increased, but device complexity increases due to multiple mixers and local oscillators
Solution Approach 1:
The system uses multiple identical mixer-digitizer modules that can be configured with different local oscillator frequencies. Each module is universal and can process any sub-band by adjusting its local oscillator, reducing the need for specialized high-bandwidth components and allowing standard lower-bandwidth digitizers to be reused across multiple frequency ranges.
Solution Approach 2:
The local oscillators are configured with specific frequency relationships (overlapping frequency ranges) that dynamically allow the system to capture and process wide bandwidth signals. The frequency shifting is dynamic and adjustable, allowing the same hardware configuration to adapt to different input signal frequency ranges by changing local oscillator frequencies.
3Adaptability or versatility
If multiple digitizers are used to capture different frequency sub-bands, then acquisition bandwidth is increased, but loss of information increases due to frequency shifting and reconstruction
Solution Approach 1:
The system captures signals from multiple frequency sub-bands simultaneously using multiple digitizers, then reconstructs the original wideband signal by combining the digitized sub-bands in the frequency domain. This feedback-based reconstruction process ensures that no information is lost during the frequency shifting process, as the original frequency components are recovered through inverse Fourier transformation and proper spectral alignment.
Solution Approach 2:
Bandpass filters are used to pre-separate the input signal into distinct frequency sub-bands before mixing and digitization. This preliminary frequency separation ensures that each digitizer captures a clean, non-overlapping portion of the spectrum, preventing aliasing and information loss during the subsequent frequency shifting and reconstruction processes.
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 solution increases the acquisition bandwidth of test and measurement instruments, allowing for efficient reconstruction of wide band signals without the bandwidth limitations of traditional digitizers, while reducing development costs and complexity.
Implementation Method 1
a first mixer is configured to mix the input signal with a first combined signal to produce a frequency shifted signal
Data Source
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AI summary
An apparatus and method for splitting a wide band input signal (105) and overlaying multiple frequency bands on each path associated with one or more digitizers (170 to 176). All frequencies from the split signal on each path can be fed to a mixer (130 to 145). The local oscillator input of each mixer receives a sum (191 to 197) of signals, which can each be set to any arbitrary frequency, as long as an associated matrix determinant of coefficients is non-zero. Each oscillator signal is multiplied by a coefficient (a1 to d4), which can represent phase and magnitude, prior to summing the oscillator signals together. Each mixer mixes a combined signal (191 to 197) with the input, thereby generating a signal set (110 to 125) of multiple overlaid frequency bands. The digitized signals are processed to substantially reconstruct the original input signal. Thus, the wide band input signal is digitized using multiple individual digitizers. In particular, a system can support two wide band signals using four digitizers of narrower bandwidth.