RF Carrier Frequency Compensation for Modulation Shift
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Solution Overview
Problem
Remote control systems, such as garage door openers, face performance issues due to frequency shifts in RF control signals caused by RF characteristics of the transmitter circuitry, particularly when data is modulated, leading to a wider bandwidth that may not be compatible with the narrower receiving bandwidth of the receiver.
Innovation Solution
A method and system that compensates for frequency shifts by measuring the carrier signal frequency, comparing it to a desired frequency, and applying a correction if necessary, using a voltage controlled oscillator circuit and control circuit to maintain the carrier frequency within the desired range, especially when data is not being modulated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If data is modulated on the carrier signal during transmission, then the control information is successfully transmitted to the receiver, but the frequency of the carrier signal shifts causing wider bandwidth that is incompatible with the narrow receiving bandwidth
Solution Approach 1:
The patent applies preliminary action by measuring the carrier frequency and determining the frequency shift amount before data modulation occurs. The system calculates the correction amount in advance and applies it to the VCO control voltage before modulation begins, preventing the frequency shift from occurring during the actual data transmission. This proactive approach ensures the carrier frequency remains stable during modulation, maintaining compatibility with the receiver's narrow bandwidth while still allowing control information to be transmitted.
2Reliability
If the carrier frequency is corrected during data modulation, then the frequency stability is improved, but the correction may interfere with the ongoing modulation process
Solution Approach 1:
The patent implements periodic action by dividing the transmission process into distinct phases: a frequency measurement and correction phase before modulation, and a data modulation phase. The system periodically measures the carrier frequency, determines correction amounts, and applies corrections during non-modulation periods. This periodic separation ensures that frequency corrections are applied only when appropriate, preventing interference with the ongoing modulation process while maintaining frequency stability across transmission cycles.
3Object-affected harmful factors
If the receiving bandwidth is kept narrow for selective reception, then interference from other frequencies is reduced, but the system cannot accommodate frequency shifted signals
Solution Approach 1:
The patent applies feedback by implementing a frequency measurement and correction loop that continuously monitors the carrier frequency and adjusts it to maintain stability. The system measures the actual carrier frequency, compares it to the desired frequency, determines the shift amount, and applies corrective voltage to the VCO. This feedback mechanism ensures the transmitted signal remains within the receiver's narrow bandwidth, allowing the system to maintain both narrow bandwidth for interference rejection and adaptability through active frequency control.
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 solution ensures stable and effective transmission of RF control signals by maintaining the carrier frequency close to the desired value, improving the compatibility and performance of the remote control system by preventing frequency shifts during data modulation.
Implementation Method 1
generating a carrier signal having a frequency... using a voltage controlled oscillator circuit
Implementation Method 2
measuring the frequency of the carrier signal... the control circuit is configured to measure the carrier frequency
Implementation Method 3
applying a correction to the carrier signal frequency... to maintain the carrier frequency within the desired range
Data Source
AI summary
A method for compensating for frequency shifts during transmission of an RF control signal includes receiving a request to enter a transmission mode from a user. A carrier signal having a frequency is generated and the frequency of the carrier signal is measured. The measured frequency of the carrier signal is compared to a desired frequency to determine if there is a difference between the measured frequency and the desired frequency. If there is a difference, it is determined if data is being modulated on the carrier signal. If data is not being modulated on the carrier signal, a correction is applied to the carrier signal frequency.