RF Receiver Frequency Control for Adjacent Channel Rejection
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Solution Overview
Problem
Existing broadcasting systems face challenges in integrating multiple digital broadcasting standards like DAB and DVB due to interference from adjacent channel signals (ACS), which increases costs and reduces system sensitivity, as they require multiple SAW filters and higher bit-number ADCs to handle different bandwidths.
Innovation Solution
A signal receiving apparatus comprising a frequency converting circuit, a computing circuit, and a control circuit that adjusts converting frequencies to generate converted signals, allowing the system to operate at optimal frequencies and filter out ACS interference, enabling the use of a single SAW filter for multiple standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple SAW filters with different bandwidths are used to integrate various broadcasting standards, then the receiving system can receive signals complying with different standards, but the system cost will increase
Solution Approach 1:
The patent implements a universal receiving system that uses a single SAW filter with fixed bandwidth to receive multiple broadcasting standards (DVB-T with 6/7/8 MHz bandwidth and DAB with 1.536 MHz bandwidth). The system achieves multi-functionality by dynamically adjusting the tuner's center frequency and the digital low-pass filter's cutoff frequency according to the selected standard, eliminating the need for multiple hardware filters and reducing system cost.
2Device complexity
If a single SAW filter is used to select DVB-T channels, then the system structure is simplified, but adjacent channel signals (ACS) with large strength will interfere with the receiving sensitivity
Solution Approach 1:
The patent extracts and removes adjacent channel signals (ACS) from the received signal through digital signal processing. A digital low-pass filter is configured with a cutoff frequency that selectively attenuates the ACS components while preserving the desired channel signal. The system calculates the ACS frequency based on the tuner center frequency and channel spacing, then applies appropriate filtering to eliminate the interference before further processing.
Solution Approach 2:
The patent implements dynamic adjustment of the digital low-pass filter's cutoff frequency based on the selected broadcasting standard and channel configuration. For DVB-T reception, the cutoff frequency is set to pass the desired channel while blocking adjacent channels. For DAB reception, the cutoff frequency is adjusted to accommodate the narrower 1.536 MHz bandwidth. This dynamic reconfiguration allows the same hardware filter to optimally perform for different standards without compromising receiving sensitivity.
3Reliability
If the ADC and digital circuit use more bit-number (resolution) to handle ACS interference, then the system can process the interference, but the system cost and complexity will increase
Solution Approach 1:
The patent applies preliminary filtering action before the ADC conversion stage by configuring the digital low-pass filter to attenuate adjacent channel signals early in the signal chain. By removing the ACS components before they enter the high-resolution digital processing stages, the system avoids the need for excessive bit-depth ADCs and complex digital signal processing algorithms that would be required to handle strong ACS interference, thereby reducing overall system cost and complexity while maintaining reliable signal processing capability.
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 approach reduces ACS interference, improves system sensitivity, and allows the same SAW filter to process signals from different standards, thereby enhancing the efficiency and cost-effectiveness of the RF signal receiving system.
Implementation Method 1
a frequency converting circuit (611) for converting a received signal (RF signal) according to a converting frequency to generate a converted signal
Data Source
AI summary
A signal receiving apparatus includes a frequency converting circuit, a computing circuit, and a control circuit. The frequency converting circuit is for converting a RF signal to respectively generate a first converted signal and a second converted signal according to a first converting frequency and a second converting frequency. The computing circuit is for computing signal quality parameters of the first converted signal and the second converted signal. The control circuit is for outputting a control signal according to the signal quality parameters of the first converted signal and the second converted signal, wherein the control signal corresponds to the converting frequency of the frequency converting circuit.