NLTL Frequency Multiplier Input Filter for Phase Noise Reduction
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Solution Overview
Problem
Conventional comb generators, particularly those using step recovery diodes, introduce substantial phase noise and limit frequency range and harmonic spacing, while nonlinear transmission line (NLTL) generators improve phase noise but can still suffer from residual noise issues, especially due to interactions with 1/f noise.
Innovation Solution
Incorporating a noise reduction filter configured to pass the input signal frequency and reject low frequencies, directly coupled to the NLTL, which reduces phase noise in both the main and side lobes of the frequency-multiplied signal, using a low-order filter to maintain simplicity and cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If step recovery diodes are used in comb generators, then frequency multiplication can be achieved, but substantial phase noise is introduced and frequency range is limited
Solution Approach 1:
The patent extracts and removes the harmful 1/f noise components from the input signal spectrum before the signal enters the NLTL frequency multiplier. By using a noise reduction filter to eliminate low-frequency noise components that would otherwise be upconverted to the output frequency, the system achieves dramatically improved phase noise performance while maintaining the broadband capabilities of the NLTL architecture.
Solution Approach 2:
The patent segments the frequency multiplication function into two distinct stages: first, a noise reduction filter removes harmful low-frequency noise components from the input signal; second, the NLTL performs the frequency multiplication function. This segmentation allows each component to be optimized independently - the filter for noise reduction and the NLTL for broadband frequency multiplication.
2Measurement precision
If high-order filters are used to reduce phase noise, then noise attenuation improves, but device complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by removing the harmful 1/f noise components from the input signal before frequency multiplication occurs. By pre-filtering the input signal to eliminate low-frequency noise that would be upconverted to the output frequency, the system achieves effective noise reduction without requiring complex high-order filters at the output stage.
Solution Approach 2:
The noise reduction filter acts as an intermediary component between the input signal source and the NLTL frequency multiplier. This intermediary filter selectively removes harmful low-frequency noise components while passing the desired input signal, thereby improving overall phase noise performance without requiring complex filtering at the output stage.
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 noise reduction filter effectively attenuates both side lobe and main lobe phase noise components, providing improved performance without the complexity and cost of high-order filters, with a 5th order HPF and BPF implementation demonstrating significant noise reduction.
Implementation Method 1
A non-linear transmission line (NLTL) is configured to time delay the electrical signal as a function of amplitude to generate electrical signals at integer multiples of the input frequency F0
Implementation Method 2
the residual phase noise is dramatically better—NLTL comb generators are exhibiting at least a 20 dB improvement over their SRD counterparts
Data Source
AI summary
A noise reduction filter is inserted between the source and non-linear transmission line (NLTL) in a frequency multiplier to improve phase noise performance. The noise reduction filter is suitably coupled directly to the input of the NLTL. The noise reduction filter and the output BPF are suitably low complexity filters.