Wireless Microphone Receiver Phase Locking for Frequency Offset Calibration
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Solution Overview
Problem
Conventional digital wireless microphone systems require a frequency offset of less than 1 ppm for stable transmission, but typically experience offsets greater than 20 ppm due to susceptibility to interference and lack of high-fidelity sound transmission.
Innovation Solution
A wireless microphone receiver system with a phase locker, calculator, and calibrator that locks the phase of received audio data, calculates and calibrates frequency offsets using both coarse and fine tuning steps, and buffers audio data to adjust for offset discrepancies, ensuring output quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a digital wireless microphone system is used, then high-fidelity sound transmission is achieved, but the frequency offset requirement becomes very strict (less than 1 ppm)
Solution Approach 1:
The system performs preliminary frequency offset estimation and compensation before the actual audio transmission. The receiver estimates the frequency offset using training sequences or pilot signals, then applies pre-compensation to the local oscillator frequency, ensuring that the strict 1 ppm requirement is met before data transmission begins.
Solution Approach 2:
The system continuously monitors the frequency offset between transmitter and receiver, feeds this information back to the frequency correction module, and dynamically adjusts the local oscillator frequency to maintain the offset within 1 ppm, ensuring stable digital transmission.
2Measurement precision
If conventional analog modulation is used, then the frequency offset requirement is relaxed, but the system becomes susceptible to interference and loses audio information
Solution Approach 1:
The patent replaces analog modulation mechanisms with digital modulation and processing. By using digital signal processing for modulation, transmission, and demodulation, the system achieves both digital immunity to interference and the ability to maintain signal integrity, while the frequency offset issue is handled through digital frequency estimation and correction algorithms.
3Ease of operation
If the frequency offset is not calibrated, then the system operation is simple, but the transmission stability deteriorates due to offset greater than 20 ppm
Solution Approach 1:
The frequency calibration function operates automatically without user intervention. The system self-calibrates by estimating the frequency offset using training sequences, calculating the offset magnitude, and automatically adjusting the local oscillator frequency to compensate for the offset, maintaining transmission stability while keeping operation simple.
Solution Approach 2:
The system performs frequency calibration automatically during the initialization phase or continuously in the background before actual audio transmission. This preliminary frequency correction ensures that when audio transmission begins, the frequency offset is already compensated, maintaining stability without requiring user action.
Data Source
AI summary
A wireless microphone receiver comprises a phase locker to lock a phase of an audio data successfully received from a microphone transmitter; a calculator to calculate a frequency offset between the locked phase of the microphone receiver and the phase of the microphone transmitter; a calibrator to calibrate the frequency offset using a first step if the absolute value of the frequency offset is larger than a first predetermined threshold, and to calibrate the frequency offset with a second step if the absolute value of the frequency offset is smaller than or equal to the first predetermined threshold, and complete the calibration if a calibrated frequency offset is smaller than a second threshold; a buffer to buffer the audio data received from the microphone transmitter, and the calibrator further adjusts the amount of data stored in the buffer; and the microphone receiver further outputs buffered audio data.