Auto-Calibrating Demodulator for TV Receiver Noise Reduction
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Solution Overview
Problem
Conventional digital/analog TV receivers suffer from noise interference and significant variations in output voltage swing due to separate PCB placement of demodulators and decoders, as well as manufacturing errors and power supply fluctuations, leading to errors in signal transmission.
Innovation Solution
A digital/analog TV receiver with an auto-calibration mechanism that integrates a demodulator, decoder, and resistor on the same PCB, using a current digital-to-analog converter (IDAC), a comparator, and a calibration apparatus to adjust the output voltage swing without an external 75Ω resistor, reducing power consumption by increasing the resistance of the external resistor and eliminating deviations caused by manufacturing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the demodulator and decoder are disposed on separate PCBs with 75Ω precision resistors for impedance matching, then the signal transmission impedance is matched, but the receiver area cannot be reduced and noise interference increases
Solution Approach 1:
The patent merges the demodulator and decoder onto a single PCB, eliminating the need for separate PCBs and coaxial lines. This integration reduces the overall receiver area while maintaining signal transmission stability through on-PCB trace routing instead of external coaxial connections.
Solution Approach 2:
The patent extracts the impedance matching function from external 75Ω precision resistors and implements it through on-PCB trace design and integration. This eliminates the need for separate impedance matching components while reducing noise interference from external connections.
2Reliability
If 75Ω precision resistors are used for impedance matching, then the impedance matching is achieved, but manufacturing errors cause noticeable variation in output voltage swing
Solution Approach 1:
The patent implements an auto-calibration mechanism that uses feedback to detect and correct output voltage swing variations. The system measures the actual output voltage and adjusts internal parameters to compensate for manufacturing tolerances, eliminating the need for high-precision external resistors.
Solution Approach 2:
The patent changes the resistance value of the external resistor from the conventional 75Ω to a higher value (e.g., 300Ω) to reduce power consumption. The auto-calibration system compensates for this parameter change by adjusting internal circuit parameters to maintain signal transmission accuracy.
3Use of energy by moving object
If the external resistor resistance is increased to reduce power consumption, then power consumption decreases, but the impedance matching and signal transmission accuracy deteriorate
Solution Approach 1:
The auto-calibration mechanism continuously monitors signal transmission quality and adjusts internal circuit parameters to compensate for the effects of using a higher-value external resistor. This feedback loop ensures that signal transmission accuracy is maintained despite the increased resistor value that reduces power consumption.
Solution Approach 2:
The patent deliberately changes the external resistor value from 75Ω to a higher value (e.g., 300Ω) to reduce power consumption by a factor of 4. The system then uses parameter adjustment through auto-calibration to compensate for this change and maintain signal transmission accuracy.
4Ease of manufacture
If separate PCBs are used for demodulator and decoder, then impedance matching is simplified, but noise interference from external connections increases
Solution Approach 1:
By merging the demodulator and decoder onto a single PCB, the patent eliminates external coaxial line connections that are sources of noise interference. The integration maintains impedance matching through carefully designed on-PCB traces while removing the harmful external connection path.
Data Source
AI summary
A demodulator comprises a reference voltage generating circuit for generating a reference voltage, a reference resistor for converting the reference voltage to a reference current, a current digital-to-analog converter (IDAC) for receiving a digital code and generating an output signal, a comparison apparatus for comparing the reference voltage with the output signal to generate a comparison output, and a calibration apparatus for updating the digital code according to the comparison output to calibrate the IDAC.