RF-DAC Radar Modulation via Integer PLL and Digital Front End
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Solution Overview
Problem
Current radar signal modulation techniques, such as those using multi-modulus feedback frequency dividers, introduce fractional spurs and phase noise, which reduce the precision of range determination and signal-to-noise ratio due to fractional switching and phase-locked loop momentum, leading to inaccuracies in frequency ramp modulation and increased noise.
Innovation Solution
A phase-locked loop generates a series of clock signals for a digital front end to produce digital signal modulation, with a radiofrequency digital-to-analog converter creating an analog signal that is upconverted to the radar frequency, using an integer feedback frequency divider to avoid fractional spurs and phase noise, and a digital signal modulator generating quadrature representations of the modulation signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-modulus feedback frequency dividers are used for radar signal modulation, then the signal can be generated at radar frequency, but fractional spurs and phase noise are introduced that reduce measurement precision and signal-to-noise ratio
Solution Approach 1:
The patent extracts and removes the harmful fractional switching operation from the frequency synthesis path by replacing the multi-modulus feedback frequency divider with an integer feedback frequency divider combined with a digital modulator. This separation eliminates the source of fractional spurs and phase noise while preserving the frequency modulation functionality.
Solution Approach 2:
The patent replaces the analog/mixed-signal frequency division mechanism (multi-modulus feedback frequency divider) with a digital-based approach (integer feedback frequency divider plus digital signal modulator). This substitution eliminates the mechanical-like switching artifacts that cause fractional spurs and phase noise.
2Object-generated harmful factors
If integer feedback frequency divider is used to avoid fractional spurs, then signal-to-noise ratio is enhanced, but device complexity increases due to additional digital modulation components
Solution Approach 1:
The patent introduces a digital modulator as an intermediary component between the integer feedback frequency divider and the RF-DAC. This mediator performs the frequency modulation function that was previously handled by the multi-modulus divider, allowing the use of a cleaner integer divider while restoring the necessary modulation capability.
3Stability of the object's composition
If phase-locked loop momentum is present in frequency ramp modulation, then frequency stability is maintained, but approximation errors increase reducing range determination accuracy
Solution Approach 1:
The patent applies preliminary digital modulation to the frequency ramp signal before it reaches the phase-locked loop output stage. By pre-modulating the digital representation of the ramp signal, the system achieves frequency modulation without relying on the phase-locked loop's momentum, thereby eliminating approximation errors while maintaining frequency stability.
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 reduces approximation errors, attenuates overshoot and undershoot in the frequency ramp, and enhances signal-to-noise ratio by avoiding fractional spurs and phase noise, providing more precise range determination and architectural flexibility in radar signal modulation.
Implementation Method 1
translating the first digital value and the second digital value with a radiofrequency digital-to-analog converter to generate the analog signal
Implementation Method 2
A phase-locked loop generates a series of clock signals for a digital front end
Implementation Method 3
by mixing a signal at an initial (low) frequency with a mixing frequency to produce a higher-frequency signal at approximately the sum of the initial frequency and the mixing frequency
Implementation Method 4
by mixing a signal at an initial (high) frequency and a mixing frequency to produce a lower-frequency signal at approximately the difference of the initial frequency and the mixing frequency
Data Source
AI summary
Radar frequency range signals (e.g., 1 to 100 gigahertz) are often generated by upconverting a reference frequency to a transmission frequency, and a received signal may be downconverted to analyze information encoded on the transmission via modulation. Modulation may be achieved via a fractional frequency divider in a phase-locked loop, but fractional spurs may reduce the signal-to-noise ratio. Additionally, the ramp slope may vary due to phase-locked loop momentum. Instead, a clock generator may generate clock signals for a digital front end comprising a digital signal modulator that generates modulated digital values comprising quadrature representations of a radar modulation signal, which are encoded by a radiofrequency digital-to-analog converter (RF-DAC). The RF-DAC analog signal may be upconverted to a radar frequency and transmitted. A receiver may receive, downconvert, and analyze a reflection of the radar transmission, e.g., to perform range detection based on a frequency ramp encoded by the radar transmission.