Variable Frequency Multiplier With NLTL Tone Selection
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Solution Overview
Problem
Current signal generators for RF communications face challenges in generating multi-tone signals with low phase noise, as existing solutions like banks of multipliers are large, power consumptive, and inefficient, while alternatives like step recovery diodes and non-linear transmission lines (NLTLs) degrade phase noise and system noise figure due to poor conversion efficiency and matching issues.
Innovation Solution
A variable frequency multiplier circuit using a non-linear transmission line (NLTL) generates a comb of frequency tones, followed by a signal separating circuit to distinguish desired tones from undesired idler tones, with amplifiers and a switched filter bank to ensure immediate amplification and proper termination of undesired tones, maintaining a good signal-to-noise ratio and minimizing phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If banks of multipliers and accompanying circuitry are used to generate multi-tone signals, then frequency stability and low phase noise are achieved, but device size, cost, and power consumption increase substantially
Solution Approach 1:
The patent combines multiple functions (frequency multiplication, tone selection, filtering) into a single integrated NLTL-based circuit module, replacing the need for separate multiplier banks and their accompanying circuitry. This merging achieves compact size while maintaining low phase noise performance.
Solution Approach 2:
The NLTL circuit serves multiple functions simultaneously: it generates the comb of frequency tones, provides frequency multiplication, enables tone selection through switching, and performs filtering. This multi-functionality eliminates the need for separate dedicated circuits for each function, reducing overall device complexity.
2Device complexity
If step recovery diodes are used to generate frequency combs, then device size is reduced, but phase noise performance degrades significantly
Solution Approach 1:
The patent modifies the operating parameters and circuit configuration of the NLTL to optimize both size and phase noise performance. By carefully controlling the nonlinearity parameter and impedance matching, the circuit achieves compact dimensions while maintaining low phase noise, unlike step recovery diodes which inherently degrade phase noise.
3Device complexity
If non-linear transmission lines are used for frequency multiplication, then device size is reduced, but conversion efficiency and noise figure deteriorate due to poor matching
Solution Approach 1:
The patent introduces impedance matching networks as intermediary circuits between the NLTL and connected components. These matching networks serve as mediators that transform impedances to achieve optimal power transfer and conversion efficiency, eliminating the poor matching inherent in NLTL-based designs.
Solution Approach 2:
The patent optimizes the electrical parameters (impedance, length, characteristic impedance) of the NLTL and its surrounding circuitry to maximize conversion efficiency. By carefully adjusting these parameters, the circuit achieves good power transfer ratios while maintaining compact size.
4Ease of operation
If conventional filters are used with NLTLs to select desired tones, then frequency selection is achieved, but output power degrades due to reflective out-of-band rejection causing tone cancelation
Solution Approach 1:
The patent converts the inherently reflective nature of conventional filters from a harmful effect into a beneficial one by designing the filter bank to reflect undesired tones back through the NLTL in a controlled manner. This controlled reflection, combined with proper switching, actually enhances the rejection of unwanted tones while preserving desired output power.
Solution Approach 2:
The patent employs dynamically switched filters where the filter configuration changes based on the desired output frequency. This dynamic switching allows the system to optimize both tone selection and output power for each operating condition, avoiding the fixed compromises of static filter designs.
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
The solution provides a compact, ultra-low noise, and cost-effective frequency multiplier circuit that rejects undesired tones without reflecting them back, improving phase noise stability and system noise figure, suitable for small form factor applications like PXI chassis and frequency synthesizers.
Implementation Method 1
A variable frequency multiplier circuit uses a non-linear transmission line (NLTL) to generate a comb of frequency tones
Data Source
AI summary
A variable frequency multiplier circuit for frequency multiplying an input signal provided by an ultra-low phase noise signal source includes a tone generator configured to generate a multiple tones from the input signal; a signal separating circuit configured to separate the multiple tones into tones of interest and idler tones, where the tones of interest are separated into one or more groups and outputted from the signal separating circuit, and the idler tones are terminated; an amplification circuit configured to amplify each group of the tones of interest to optimize small and large signal responses; and a switched filter bank configured to selectively connect a selected tone from the tones of interest to a circuit output.