FM Reception Device DC Offset Correction IQ Plane Centering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Direct conversion FM reception devices face issues with distortion and noise due to the reduction of direct current components in the base band signal, leading to incomplete signal reception and noise detection when an unmodulated signal is received, and distortion in modulated signals when DC components are suppressed.
Innovation Solution
An FM reception device with a modulation frequency generation unit, local oscillator, quadrature detection unit, reduction unit, correction unit, FM detection unit, addition unit, Auto Frequency Controller (AFC) unit, and selection unit that generates and corrects base band signals to center them around the origin of the IQ plane, adds an offset to the detection signal, and controls the local oscillation frequency to prevent signal termination and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coupling capacitor is used to reduce the direct current component in the base band signal, then the unnecessary direct current component from the amplifier is reduced, but the direct current component and low frequency component in the base band signal are also reduced, creating distortion components and causing signal termination
Solution Approach 1:
The patent separates the DC component reduction function into two stages: the coupling capacitor removes the amplifier's DC offset, while the correction unit restores the signal's DC component. This segmentation allows each unit to perform its specific function without interfering with the other, resolving the contradiction between removing unwanted DC and preserving signal integrity
Solution Approach 2:
The correction unit acts as an intermediary between the coupling capacitor and the FM detection unit. It receives the DC-reduced signal from the capacitor, restores the necessary DC component by centering the IQ plane around the origin, and outputs the corrected signal to the FM detection unit, thereby preventing signal termination while maintaining DC reduction benefits
2Object-generated harmful factors
If the direct current component is reduced by the coupling capacitor, then the DC offset from the amplifier is eliminated, but when an unmodulated signal is received, the entire signal is cut off and only noise remains for FM detection
Solution Approach 1:
The correction unit performs preliminary action by restoring the DC component before the signal reaches the FM detection unit. By centering the IQ plane around the origin in advance, the system ensures that unmodulated signals are preserved and can be properly detected, preventing the signal cutoff that would otherwise occur
Solution Approach 2:
The system uses feedback from the IQ plane positioning to control the correction amount. The correction unit continuously monitors the base band signal's position and adjusts the DC restoration to maintain the IQ plane centered around the origin, ensuring reliable reception of unmodulated signals while maintaining DC offset elimination
3Loss of energy
If the coupling capacitor reduces the direct current component, then the amplifier's DC output is minimized, but distortion components remain after FM detection
Solution Approach 1:
The patent segments the signal processing into distinct functional blocks: the coupling capacitor handles DC offset removal, while the correction unit handles signal quality restoration. This segmentation allows the system to achieve both DC reduction and distortion elimination by assigning each function to the appropriate component
Solution Approach 2:
The correction unit serves as an intermediary that receives the DC-reduced but distorted signal from the coupling capacitor, restores the necessary DC component through IQ plane centering, and outputs a clean signal to the FM detection unit, thereby eliminating distortion while maintaining DC reduction
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 effectively prevents signal termination and distortion, improving the quality of FM detection by maintaining a stable frequency offset and correcting the DC component in the base band signal, ensuring accurate demodulation and reducing noise in the detection signal.
Implementation Method 1
a local oscillator that outputs a local oscillation signal frequency-modulated by using the modulation signal from the modulation frequency generation unit
Implementation Method 2
a quadrature detection unit that subjects an FM signal to quadrature detection by using the local oscillation signal output from the local oscillator and outputs a base band signal
Data Source
AI summary
A first local oscillator generates a modulation signal of a predetermined frequency. A second local oscillator outputs a local oscillation signal frequency-modulated by using the modulation signal from the first local oscillator. A quadrature detection unit subjects an FM signal to quadrature detection by using the local oscillation signal output from the second local oscillator and outputs a base band signal. A first reduction unit and a second reduction unit reduce a direct current component contained in the base band signal. A correction unit restores the direct current component by correcting the base band signal such that the base band signal is centered around an origin of a polar coordinate system on an IQ plane. An FM detection unit subjects the corrected base band signal to FM detection and generates a detection signal.