Shift Control Circuit for FM Wireless Devices
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Solution Overview
Problem
In frequency modulation (FM) wireless devices, the variability in maximum frequency shift per frequency is significant due to severe suppression of harmonic components by digital splatter filters, making it difficult to maintain the maximum frequency shift at a prescribed value, especially at frequencies corresponding to the minimum value of the maximum frequency shift.
Innovation Solution
A shift control circuit is introduced that includes a limiter circuit to limit the amplitude of input signals, a phase shifter to shift the phase of frequency components within a predetermined range, and a harmonic suppressor to suppress frequency components above a certain threshold, thereby stabilizing the maximum frequency shift. The phase shifter can be an all-pass filter with an infinite impulse response (IIR) and the harmonic suppressor a finite impulse response (FIR) filter, or a single splatter filter with IIR characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If digital splatter filters severely suppress harmonic components, then spectral purity is improved, but variability in maximum frequency shift per frequency increases
Solution Approach 1:
The patent implements feedback by measuring the actual maximum frequency shift at different frequencies and using this information to adjust the splatter filter characteristics. The system continuously monitors the frequency shift variability and modifies the filter's suppression characteristics to compensate for observed variations, thereby maintaining consistent maximum frequency shift while preserving harmonic suppression effectiveness.
Solution Approach 2:
The patent applies dynamics by making the splatter filter characteristics adjustable rather than fixed. The filter's suppression characteristics are dynamically modified based on the operating frequency and observed frequency shift behavior. This allows the system to adapt the degree of harmonic suppression to maintain consistent maximum frequency shift across different operating conditions.
2Stability of the object's composition
If the maximum frequency shift is maintained at a prescribed value, then modulation consistency is improved, but the complexity of the control circuit increases
Solution Approach 1:
The patent changes parameters by adjusting the splatter filter's characteristics (such as cutoff frequency or suppression depth) based on the operating frequency and observed frequency shift behavior. Rather than adding complex active control elements, the system modifies filter parameters to achieve consistent maximum frequency shift, thereby maintaining modulation consistency with relatively simple circuit modifications.
3Object-generated harmful factors
If harmonic components are severely suppressed, then spectral purity is improved, but modulation accuracy deteriorates
Solution Approach 1:
The patent applies dynamics by making the splatter filter characteristics adjustable rather than fixed. The filter's suppression characteristics are dynamically modified based on the operating frequency and observed frequency shift behavior. This allows the system to adapt the degree of harmonic suppression to maintain consistent maximum frequency shift across different operating conditions.
Data Source
AI summary
A signal input from a microphone is A-D converted by an A-D converter, is frequency differentiated by a pre-emphasis circuit, and is input to a shift control circuit. The shift control circuit includes a limiter circuit, a phase shifter, and a harmonic suppressor. The limiter circuit performs amplitude limitation so as to limit the amplitude of the input control target signal to be equal to or less than a first threshold. The phase shifter shifts, for the control target signal having the amplitude limited, a phase of a frequency component within the predetermined frequency range. The harmonic suppressor suppresses, for the control target signal phase-shifted by the phase shifter, a frequency component equal to or greater than a second threshold, and outputs an information signal that is the control target signal having the frequency component of equal to or greater than the second threshold suppressed. The modulator performs frequency modulation on a carrier wave in accordance with the information signal. The transmitter produces a transmission signal from the frequency-modulated carrier wave, and transmits the transmission signal via an antenna.