Digital TV Demodulator Circuit Frequency Synchronization
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Solution Overview
Problem
Conventional digital television receivers face difficulties in performing frequency and symbol synchronization due to noise, especially in terrestrial receiving systems with multiple paths, which affects receiving performance.
Innovation Solution
A demodulation circuit and method that includes a polyphase filter, complex multiplication unit, carrier restoration circuit, matched filter, sort circuit, DC removal circuit, sampling rate control circuit, and symbol timing restoration circuit to adjust error rates and perform frequency synchronization, even with large frequency errors, by converting and processing digital intermediate frequency signals into desired data rates and removing frequency offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency and symbol synchronization are performed using conventional methods in terrestrial receiving systems with multiple paths, then the receiving system can process signals, but the synchronization accuracy deteriorates due to noise
Solution Approach 1:
The patent applies preliminary action by performing frequency synchronization before symbol synchronization in the signal processing sequence. The frequency synchronization unit corrects carrier frequency offset first, creating a cleaner signal foundation for subsequent symbol synchronization. This preliminary frequency correction reduces the noise impact on the overall synchronization process by establishing accurate frequency reference before timing recovery attempts.
Solution Approach 2:
The patent segments the synchronization process into two distinct functional units: frequency synchronization and symbol synchronization. By dividing the synchronization task into separate stages with dedicated processing units, the system can optimize each stage independently and apply appropriate noise mitigation techniques specific to each synchronization type, thereby improving overall measurement precision despite noisy multiple-path conditions.
2Reliability
If equalizer performance is increased to improve receiving performance, then receiving performance improves, but the system complexity increases
Solution Approach 1:
The patent applies preliminary action by implementing frequency and symbol synchronization before equalization processing. By establishing accurate timing and frequency reference in advance, the input signal to the equalizer is pre-conditioned, reducing the equalizer's burden and allowing it to achieve better receiving performance with relatively simpler structure. The synchronization units prepare the signal by removing frequency offset and timing errors that would otherwise complicate equalization.
3Measurement precision
If frequency synchronization is performed with large frequency errors using conventional methods, then frequency synchronization can be attempted, but the synchronization accuracy deteriorates
Solution Approach 1:
The patent applies parameter changes by using a frequency synchronization unit that can adapt its processing based on the magnitude of frequency offset. The unit employs algorithms that adjust their parameters according to the detected frequency error, enabling effective synchronization even when large frequency errors are present. This dynamic parameter adjustment allows the system to maintain synchronization accuracy across varying frequency offset conditions.
Solution Approach 2:
The frequency synchronization unit implements dynamic processing that adapts to the actual frequency error conditions. Rather than using fixed synchronization parameters, the system dynamically adjusts its frequency correction approach based on the detected offset magnitude, enabling it to handle both small and large frequency errors effectively while maintaining synchronization precision.
Data Source
AI summary
An apparatus may include a sort circuit for receiving first and second baseband signals, where the sort circuit shifting frequencies of the first and second baseband signals. The apparatus may also include a removal circuit for receiving the shifted first and second baseband signals and for combining the shifted first and second baseband signals to provide a frequency-modulated signal, and a symbol timing restoration circuit for measuring a timing error in related symbols of the frequency-modulated signal, for generating an address selection signal that is proportional to the timing error, in response to a carrier restoration signal, and for indicating restoration of the carrier.