Modulator DC Offset Cancellation Using Envelope Feedback
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Solution Overview
Problem
DSBSC modulators face challenges in suppressing carrier signals due to manufacturing tolerances, leading to DC offsets that cause interference and make signal demodulation difficult, with existing solutions either complex or costly to implement.
Innovation Solution
A DC offset cancellation circuit that measures the sign and digitized ripple polarity of the RF envelope to generate a compensation signal, simplifying the circuit structure and eliminating the need for analog-to-digital conversion, allowing for effective cancellation of DC offsets without complex calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If DSBSC modulator is used to suppress carrier signal, then transmission efficiency is improved, but manufacturing tolerances cause DC offsets that lead to carrier leaks and interference
Solution Approach 1:
The patent implements a feedback mechanism where the modulator output is fed back through an envelope detector to generate a DC offset cancellation signal. The envelope detector extracts the envelope of the modulated signal, and this information is used to generate a cancellation signal that is added to the input signal to eliminate DC offsets and carrier leaks at the modulator output.
Solution Approach 2:
The patent introduces an envelope detector as an intermediary component between the modulator output and the DC offset cancellation mechanism. The envelope detector converts the RF modulated signal into an envelope signal that contains information about the DC offset, which then guides the generation of the cancellation signal without requiring direct measurement of the DC offset itself.
2Object-generated harmful factors
If complex DC offset cancellation circuits are implemented, then carrier suppression is improved, but circuit complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts only the essential information needed for DC offset cancellation by using an envelope detector to obtain the envelope of the modulated signal. Instead of implementing complex circuits that process the entire signal or require direct DC offset measurement, the solution extracts only the envelope information which is sufficient to generate the cancellation signal, thereby simplifying the circuit.
Solution Approach 2:
The patent employs simple, low-cost components such as an envelope detector and basic signal adders instead of complex calibration circuits or high-precision matching networks. The solution uses readily available off-the-shelf components that can be easily manufactured and integrated, avoiding the need for expensive custom-designed complex cancellation circuits.
3Object-generated harmful factors
If traditional DC offset cancellation methods are used, then carrier leak is reduced, but calibration complexity and manufacturing difficulty increase
Solution Approach 1:
The patent implements a self-calibrating system where the modulator automatically cancels its own DC offsets using feedback from its own output. The envelope detector continuously monitors the modulator output and automatically adjusts the DC offset cancellation signal without requiring external calibration equipment or manual adjustment, making the system self-sufficient and easy to manufacture.
Solution Approach 2:
The patent performs DC offset cancellation continuously in real-time rather than requiring preliminary calibration before operation. The feedback mechanism continuously generates and applies the cancellation signal, ensuring carrier suppression is maintained throughout operation without needing separate calibration steps that complicate manufacturing.
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
The solution automatically compensates DC offsets in modulators, reducing carrier leaks and improving signal integrity without increasing production complexity or cost, enabling efficient suppression of carrier signals.
Implementation Method 1
an envelope detecting unit for performing envelope detection on the RF output signal
Data Source
AI summary
A DC offset cancellation circuit used for compensating a carrier leak at an output signal of a modulator has a sign extraction unit for extracting sign of an information signal which is applied to the modulator, an envelope detecting unit for performing envelope detection on the output signal of the modulator to output the resulting envelope, a slope detecting unit for performing polarity detection on the slope of the envelope; and a signal processing unit for generating a DC offset cancellation signal for compensating the carrier leak based on the result of the sign extraction and the result of the polarity detection. The signal processing unit preferably calculates the DC offset cancellation signal by multiplying the sign of the information signal by the polarity of the slope of the envelope and accumulating the result of multiplication.