Battery Tester Detecting High-Frequency Hum via AGC Sampling
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Solution Overview
Problem
Current methods for measuring Hum in digital QAM signals, particularly in battery-operated testers, are inadequate as they require a power line for triggering and fail to evaluate unsynchronized Hum components, such as those from switching-type power supply faults, and cannot measure high-frequency Hum beyond 7.5 kHz.
Innovation Solution
A battery-powered testing device measures Hum in digital TV signals by using a DTV receiver with a QAM demodulator and automatic gain control (AGC) stages, sampling AGC values at a rate exceeding twice the Hum frequency to analyze Hum characteristics, and computes correlation between sequences to estimate Hum correlation, enabling detection of high-frequency Hum up to 1 MHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional Hum measurement methods using power line triggering are used, then synchronized Hum components can be detected, but unsynchronized Hum components from switching-type power supply faults cannot be evaluated and high-frequency Hum beyond 7.5 kHz cannot be measured
Solution Approach 1:
The patent changes the fundamental measurement parameter from power line frequency triggering to AGC (Automatic Gain Control) signal sampling. By sampling the AGC signal at a high rate (exceeding twice the maximum Hum frequency to be measured, i.e., >2 MHz for 1 MHz coverage), the system can detect Hum components across a much broader frequency range including unsynchronized and high-frequency components that traditional methods miss.
Solution Approach 2:
The patent introduces the AGC signal as an intermediary medium for Hum measurement. Instead of directly measuring the RF signal or using power line triggering, the system uses the AGC control signal that naturally reflects signal strength variations caused by Hum. This intermediary approach enables indirect but effective measurement of Hum characteristics without requiring direct access to the problematic signal sources.
2Ease of operation
If battery-operated portable testers are used, then field testing convenience is improved, but existing devices lack Hum measurement capability
Solution Approach 1:
The patent makes the battery-operated tester self-sufficient for Hum measurement by using its existing AGC circuitry and processing capabilities. The device uses its own internal AGC signal from the QAM demodulator, eliminating the need for external power line triggering or additional specialized hardware. This self-service approach enables portable devices to perform Hum measurement without compromising battery operation or portability.
Solution Approach 2:
The patent enables the battery-operated QAM signal tester to perform multiple functions: standard QAM signal quality measurement and Hum measurement. By utilizing the existing AGC circuitry and signal processing path already present in the device, the system adds Hum measurement capability without requiring separate dedicated equipment, thus achieving multi-functionality in a single portable instrument.
3Measurement precision
If sampling rate is increased to detect high-frequency Hum up to 1 MHz, then measurement frequency range is improved, but device complexity and processing requirements increase
Solution Approach 1:
The patent performs preliminary action by capturing the AGC signal at a high sampling rate and storing it in memory for later processing. This allows the system to acquire data at the required high rate (exceeding 2 MHz for 1 MHz Hum detection) without requiring complex real-time processing at that rate. The heavy lifting of high-rate sampling is done once during data acquisition, while analysis can be performed at lower rates on the stored data.
Solution Approach 2:
The patent implements dynamic processing by allowing flexible selection of sampling rates and analysis methods based on the specific measurement requirements. The system can adjust the sampling rate to match the maximum expected Hum frequency (always >2× the maximum frequency), and can process different frequency ranges with appropriate computational methods, providing dynamic adaptability rather than fixed complex hardware.
Data Source
AI summary
The invention relates to a method for measuring Hum on a digital QAM carrier using a testing device for testing digital TV signals including a QAM demodulator therein, and to a testing device implementing the method. A controller is used to sample a register associated with a final AGC stage in a QAM demodulator, and to process the collected register values to obtain one or more Hum characteristics. In one embodiment, a circular buffer is used to collect aligned sequences of AGC samples that have a pre-determined feature of time-domain Hum at a specified position therein. The aligned AGC sequences are then correlated to assess causes of Hum.