AM Digital Demodulation with Frequency-Shifted Down Conversion
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Solution Overview
Problem
Existing digital demodulation devices face challenges in accurately demodulating amplitude modulation signals due to inaccurate carrier frequencies, leading to irritating noise components, such as a 50 Hz noise, and require cumbersome calculations to correct frequency errors, resulting in a heavy processing load.
Innovation Solution
A digital demodulation device and method that perform down conversion by mixing the AM signal with sinusoidal signals of a frequency equal to the carrier frequency plus a predetermined frequency shift, ensuring the noise component is shifted beyond the sensitive range of human hearing, thereby reducing or removing it without complex calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency correction calculations are performed to accurately lock onto the carrier frequency, then the noise component is reduced, but the processing load increases heavily
Solution Approach 1:
The patent changes the frequency parameter by introducing a predetermined frequency shift (e.g., 50 Hz or 100 Hz) to the carrier frequency. Instead of performing complex calculations to achieve exact frequency locking, the system deliberately uses a slightly offset frequency, which moves the noise component to an inaudible range while significantly reducing processing complexity
Solution Approach 2:
The patent converts the harmful effect of frequency inaccuracy into a beneficial outcome. By intentionally introducing a frequency shift, the noise component that would normally be audible at low frequencies is moved to high frequencies where it becomes inaudible to humans, thus transforming a potential defect into an acceptable solution
2Measurement precision
If complex frequency locking algorithms are implemented to correct inaccurate frequency, then demodulation accuracy is improved, but device complexity increases
Solution Approach 1:
The patent simplifies the demodulation process by changing the frequency parameter from the exact carrier frequency to a shifted frequency (carrier frequency plus predetermined offset). This eliminates the need for complex frequency locking algorithms while maintaining acceptable demodulation accuracy, as the noise component is pushed to an inaudible range
3Measurement precision
If the carrier frequency is used directly for demodulation, then the demodulated result is accurate, but a noise component appears in the output signal
Solution Approach 1:
The patent transforms the harmful noise component by shifting its frequency location. By adding a predetermined frequency shift to the carrier frequency, the noise that would normally appear at low audible frequencies is moved to high frequencies beyond human hearing range, effectively eliminating the harmful effect while preserving demodulation accuracy
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
The solution effectively reduces or removes noise components by shifting them to an inaudible range, simplifying the processing load and improving demodulation performance without the need for intricate frequency locking algorithms.
Implementation Method 1
the first path digital processing represents performing down conversion by mixing the AM signal with a first sinusoidal signal whose frequency is equal to the second frequency
Data Source
AI summary
A digital demodulation device for demodulating an amplitude modulation (AM) signal whose carrier has a first frequency includes: a processing circuit for performing first path digital processing and second path digital processing according to a second frequency and digital values of the AM signal, where the first path digital processing represents performing down conversion by mixing the AM signal with a first sinusoidal signal whose frequency is equal to the second frequency, the second path digital processing represents performing down conversion by mixing the AM signal with a second sinusoidal signal whose frequency is equal to the second frequency, the second frequency is equal to the first frequency plus a predetermined frequency shift, and the second sinusoidal signal is orthogonal to the first sinusoidal signal; and an output stage for outputting an output signal according to processing results of the first path digital processing and the second path digital processing.