FSK Receiver DC Offset Correction Threshold
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Solution Overview
Problem
Existing FSK receivers face challenges in rapidly and accurately removing DC offsets from multi-level FSK signals, particularly with ternary or higher multi-ary codes, leading to difficulties in synchronizing received and transmitted frequencies due to inaccurate detection of maximum and minimum values.
Innovation Solution
An FSK receiver is designed to perform DC offset correction based on the maximum and minimum values of the demodulation signal, halting the correction operation if the difference between these values is less than a predetermined threshold, and using a threshold value greater than (the maximum frequency deviation - the minimum frequency deviation) × (n - 2) / (n - 1) for n-ary coded signals, ensuring accurate offset removal without relying on adjacent or equally deviated code pairs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC offset removal is performed using a high-pass filter, then the DC component is removed from the demodulation signal, but the DC component is lost causing deterioration in sensitivity
Solution Approach 1:
The patent extracts the DC offset component separately using a low-pass filter before removing it from the demodulation signal. This allows the DC component to be removed without losing information about the signal levels, thereby maintaining sensitivity while eliminating the harmful DC offset.
Solution Approach 2:
The patent introduces an intermediary low-pass filter that captures the DC offset component. This intermediary structure allows the DC offset to be separated and subtracted from the original signal, preventing direct loss of the DC component while still achieving offset removal.
2Object-generated harmful factors
If DC offset is extracted using a low-pass filter, then the DC offset can be removed from the demodulation signal, but the passband must be set far less than symbol rate increasing calculation amount
Solution Approach 1:
The patent applies partial action by using a low-pass filter with a passband set far less than the symbol rate, which is sufficient to extract the DC offset component without needing to process the entire signal bandwidth. This reduces the calculation amount while still achieving effective DC offset removal.
3Productivity
If offset correction is performed based on maximum and minimum values in multi-ary codes, then the correction can be performed rapidly, but accurate detection of which codes correspond to maximum and minimum values becomes difficult
Solution Approach 1:
The patent uses feedback by monitoring the difference between maximum and minimum values and comparing it against a threshold. When the difference exceeds the threshold, correction is performed; otherwise, it is halted. This feedback mechanism ensures accurate detection and correction while maintaining rapid operation.
Solution Approach 2:
The patent replaces complex code identification mechanisms with a simpler threshold-based comparison system. Instead of identifying which specific codes correspond to maximum and minimum values, the system simply compares the difference against a predetermined threshold, significantly simplifying the detection process while maintaining accuracy.
4Reliability
If correction operation is halted when signal difference is small, then erroneous corrections due to noise are prevented, but the threshold must be set appropriately to balance noise rejection and correction sensitivity
Solution Approach 1:
The patent changes the parameter of the threshold value based on the specific application requirements for multi-ary codes. By adjusting this parameter, the system can optimize the balance between noise rejection and correction sensitivity for different coding schemes without requiring complex adaptive algorithms.
Data Source
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Figure 3A~3B
AI summary
In an FSK receiver according to the present invention, a correction operation for a DC offset component is performed based on a maximum value and a minimum value of a demodulation signal. If a difference between the maximum and minimum values is less than a predetermined threshold value TH1, the correction operation is halted. Thus, the FSK receiver can rapidly perform an appropriate offset removal from a multi-level FSK signal.