NLTL Frequency Comb Topology for Odd-Harmonic Extraction
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Solution Overview
Problem
Existing NLTL frequency comb generators face challenges in generating output signals with signal power selectively concentrated at certain frequency harmonics, particularly for high N-th order harmonics, requiring high Q factor band-pass filters which are difficult to implement for low-frequency input signals.
Innovation Solution
The NLTL frequency comb generator employs a series of cascaded segments with variable shunt capacitors and inductors, where capacitance and inductance values decrease along the signal propagation path, compressing rise and fall times to generate higher frequency harmonics, and incorporates DC biasing to suppress even harmonics, allowing for natural suppression of even harmonics and reduced BPF complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a band-pass filter with high Q factor is used to reject nearby harmonics, then signal power can be selectively concentrated at certain frequency harmonics, but the device complexity and implementation difficulty increase significantly
Solution Approach 1:
The patent extracts and suppresses even harmonics specifically from the output signal using a full-wave rectifier circuit. By targeting and removing only the even harmonic components (2nd, 4th, 6th, etc.) while preserving odd harmonics (3rd, 5th, 7th, etc.), the circuit achieves selective harmonic concentration without requiring complex high-Q band-pass filters for each harmonic band.
Solution Approach 2:
The patent changes the capacitance parameters of the shunt capacitors along the signal propagation path, with base capacitance values decreasing from earlier to later segments. This parameter gradient creates varying compression effects at different stages, enabling natural harmonic generation and separation. The parameter variation allows the system to generate multiple harmonics inherently through nonlinear compression rather than requiring external filtering for each harmonic.
2Speed
If high N-th order harmonics are generated from low-frequency input signals, then frequency multiplication is achieved, but it becomes very difficult to select and filter the desired harmonic
Solution Approach 1:
The full-wave rectifier circuit extracts and removes even harmonics from the multiplied frequency signal. When low-frequency input signals are frequency-multiplied through the NLTL, both odd and even harmonics are generated. The rectifier specifically extracts and suppresses the even harmonic components, leaving the odd harmonics (including the desired high N-th order harmonics) clearly distinguishable and easier to select.
Solution Approach 2:
The patent converts the harmful effect of even harmonic generation into a beneficial filtering mechanism. Instead of treating even harmonics as unwanted interference that requires complex suppression, the circuit uses full-wave rectification to naturally generate and then selectively remove even harmonics, turning the frequency multiplication process itself into the filtering mechanism. This makes high N-th order harmonic selection from low-frequency inputs much more straightforward.
3Manufacturing precision
If capacitance and inductance values are decreased along the signal propagation path, then rise and fall time compression is improved for higher frequency harmonics, but the manufacturing precision requirements increase
Solution Approach 1:
The NLTL is divided into multiple segments along the signal propagation path, with each segment containing series inductors and shunt capacitors. By segmenting the transmission line, the patent can implement gradual capacitance and inductance value decreases in a controlled manner across segments rather than requiring precise continuous variation. This segmentation makes the manufacturing of variable L and C values more feasible while still achieving the desired time compression effect for higher frequency harmonics.
Solution Approach 2:
Different segments of the NLTL have different capacitance and inductance values, with base capacitance values decreasing from earlier to later segments. This local quality variation is deliberately designed to create the progressive time compression needed for generating higher frequency harmonics. The patent balances the manufacturing complexity by using discrete capacitor value changes at each segment rather than continuous variation, making the gradient structure manufacturable while maintaining the precision needed for time compression.
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 generation of higher frequency harmonics with reduced even harmonics, facilitating easier filtering and lower complexity in band-pass filters, thus lowering implementation costs and improving signal extraction or filtration.
Implementation Method 1
The shunt varactors have their cathodes coupled to corresponding series inductors, and the reverse varactors have their anodes coupled to corresponding series inductors. The shunt and reverse shunt capacitors may be varactors or Schottky diodes that have voltage-dependent capacitance, which decreases under increasing reverse PN junction voltage bias.
Implementation Method 2
A non-linear transmission line (NLTL) is generally an inductor-capacitor (LC) ladder network that comprises periodically loaded non-linear components, e.g., non-linear inductors or non-linear capacitors. Various NLTL frequency comb generator embodiments are disclosed to compress rising time, fall time, or both rise time and fall time of an input signal to generate an output signal comprising multiple harmonics of the input signal.
Implementation Method 3
When the input signal gets more compressed as it propagates along the NLTL frequency comb generator, it comprises more higher frequency harmonics. Subsequent segments may have series inductors, shunt capacitors, and reverse shunt capacitors in smaller sizes and inductance/capacitance values for impedance matching the increasingly higher frequency harmonics of the input signal for better comb frequency generation.
Data Source
AI summary
Various NLTL frequency comb generator embodiments are disclosed for compressing rise time, fall time, or both rise time and fall time of an input signal to generate an output signal comprising multiple harmonics of the input signal. The NLTL frequency comb generator may comprise a plurality of segments cascaded in series with each segment comprising a series inductor, a shunt capacitor, and a reverse shunt capacitor for balanced signal compression. The shunt capacitor and the reverse shunt capacitor may be varactors or Schottky diodes that have voltage-dependent capacitance. As a result, both rise time and fall time of the input signal are compressed along the NLTL frequency comb generator. With a sinusoidal signal input, the output signal may be close to a square wave. Such a square wave output naturally suppresses all even harmonics, which can be valuable for odd harmonics signal extraction or filtration.