Local Oscillator Burst Pulse Width Modulation for Spur Reduction
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Solution Overview
Problem
Existing RF receivers experience interference due to undesired local oscillator spurs caused by abrupt switching of local oscillator frequencies, leading to increased spectral bandwidth and potential receiver interference.
Innovation Solution
Implementing a two or three state local oscillator signal with time domain pulse width modulation to shape the amplitude of RF frequency pulses, reducing frequency domain component magnitudes and minimizing spectral bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If abrupt local oscillator frequency switching is used, then receiver can rapidly change between receive frequencies, but local oscillator spurs are generated causing receiver interference
Solution Approach 1:
The patent applies preliminary action by pre-shaping the amplitude envelope of the local oscillator signal before frequency switching occurs. The envelope is designed to have smooth transitions (using sinusoidal or other continuous functions) that begin before the actual frequency change, thereby preventing the abrupt transitions that generate spurs while still enabling rapid frequency switching.
Solution Approach 2:
The patent changes the amplitude parameter of the local oscillator signal over time according to a predetermined envelope function. By modulating the amplitude parameter continuously rather than switching it abruptly, the patent reduces spectral side lobes and minimizes spur generation while maintaining the ability to rapidly switch between frequencies.
2Device complexity
If square shaped amplitude envelope is used for local oscillator bursts, then simple switching is achieved, but frequency domain spectrum introduces undesired spurs reaching -13 dBc
Solution Approach 1:
The patent transforms the amplitude parameter from a simple square wave (abrupt on/off) to a continuously varying envelope function such as sinusoidal or raised cosine. This parameter change smooths the transitions in the time domain, which directly reduces the spectral side lobes and spur levels in the frequency domain while maintaining manageable system complexity.
Solution Approach 2:
The patent introduces dynamic amplitude modulation to the local oscillator signal by applying a time-varying envelope function. This dynamic control of the amplitude parameter allows the signal to smoothly transition between states, reducing abrupt changes that cause spurs, while the envelope shape can be optimized to balance complexity and performance.
3Adaptability or versatility
If periodic local oscillator frequency changing is implemented, then multiple receive frequencies are processed sequentially, but spectral bandwidth increases causing interference opportunities
Solution Approach 1:
The patent applies amplitude envelope shaping to the periodic local oscillator frequency changes. By controlling the amplitude parameter with smooth transition functions rather than abrupt switching, the spectral bandwidth of each frequency component is reduced, thereby minimizing interference opportunities while maintaining the ability to process multiple receive frequencies sequentially.
Data Source
AI summary
A method and frequency converter for a radio rapid frequency signal scanning and including a local oscillator signal synthesis source (112) producing a local oscillator signal (502) with local oscillator bursts (210). The local oscillator bursts (210) contain pulse width modulated RF frequency pulses (602). Each local oscillator burst having, for a pre-determined duration, RF frequency pulses within an effective amplitude above a pre-determined threshold (260). Each local oscillator burst (210) having also has effective amplitude pulse shaping envelope (504) that reduces at least one frequency domain component magnitude (310) of the local oscillator signal (300). A radio frequency mixer (110) receives an RF signal input (104) and the local oscillator signal to produce an output signal (160) at a frequency related to a combination of a frequency of the RF signal input and a frequency of the local oscillator signal.