NCO Step-Change Cancellation in RF Audio Demodulation
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Solution Overview
Problem
Frequency step changes in numerically controlled oscillators (NCOs) within wireless communication systems lead to noise and impulse generation in receiver circuitry, affecting the quality of audio signals by inducing step changes and impulses in demodulation outputs.
Innovation Solution
A method to determine and correct for step changes in NCO control values by generating a correction value based on the step change, which is applied to the demodulated signal to cancel noise, and optionally repeating prior demodulated samples to eliminate impulses, using digital signal processing and cancellation circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If frequency adjustments are made to tune to a desired channel, then the receiver can select and process the desired signal, but step changes in frequency control signals generate noise and impulses in demodulation circuitry
Solution Approach 1:
The patent detects step changes in the NCO control signal before they fully propagate through the demodulation circuitry. By identifying the step change event early in the signal chain, the system can apply correction to the demodulated output signal to cancel the resulting noise and impulses, preventing rather than merely remedying the harmful effects
Solution Approach 2:
The patent converts the harmful step change artifacts into a detectable signal characteristic. By monitoring the NCO control signal for step changes and using this information to generate correction values, the system transforms the presence of potential harm into a useful indicator that enables active cancellation of the harmful effects in the demodulated output
2Productivity
If discrete frequency changes are applied to the NCO, then channel selection is achieved, but impulse spikes are generated in the output audio signals
Solution Approach 1:
The patent implements a feedback mechanism where the NCO control signal is monitored for step changes, and this information feeds back to modify the demodulated output signal. The correction value generated from detecting the step change is applied back to the output signal path to cancel the impulse spikes, creating a closed-loop system that actively suppresses harmful artifacts
Solution Approach 2:
By detecting the step change in the NCO control signal and generating a correction value in advance, the system applies preliminary anti-action to counteract the impulse spikes before they fully manifest in the audio output. The correction is prepared and applied to prevent the harmful effect rather than waiting for it to occur
Data Source
AI summary
In one embodiment, the present invention includes a method for determining when a step change occurs to a control value for a numerically controlled oscillator (NCO) providing a mixing signal, mixing the mixing signal with an input radio frequency (RF) signal to obtain an intermediate frequency (IF) signal and demodulating the IF signal into a demodulated signal, generating a correction value based on the step change, and applying the correction value to the demodulated signal. Other embodiments may be used to cancel other undesired signal portions, such as impulse spikes generated from the NCO change.