FM Receiver DC Offset Correction via Phase Rotation
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Solution Overview
Problem
Direct conversion type FM receivers face signal receiving performance deterioration due to DC offset components, making it difficult to distinguish received signals from DC offsets, especially when the received signal is unmodulated and has the same frequency as the local oscillation signal, leading to false operations and poor detection signals.
Innovation Solution
The FM receiver employs a local oscillator, quadrature detector, corrector, DC offset detector, and controller to perform quadrature detection, correct DC offset, and control the local oscillation frequency to rotate phase components, ensuring the amplitudes in multiple phase domains approximate each other, thereby improving signal detection and reducing false operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polar coordinate conversion is performed on I-phase and Q-phase baseband signals to detect DC offset, then DC offset correction is achieved, but when the received signal is unmodulated and has the same frequency as the local oscillation signal, the I-phase and Q-phase signals take constant values and phase signals are always mapped into a single phase domain, making it difficult to distinguish the received signal from DC offset
Solution Approach 1:
The patent applies the dynamics principle by controlling the local oscillator to rotate the phase component of the received signal at a predetermined rotation speed. This dynamic phase rotation transforms the stationary constant values of I-phase and Q-phase signals into time-varying signals, enabling the DC offset detector to distinguish between DC offset (which remains constant) and the rotated signal components. The rotation creates temporal variation that allows reliable detection and separation of DC offset from the actual signal.
Solution Approach 2:
The patent implements preliminary anti-action by pre-rotating the phase component of the received signal before DC offset detection. By rotating the signal phase in advance at a controlled speed, the system prevents the scenario where signal and DC offset become indistinguishable. This preliminary phase rotation ensures that when polar coordinate conversion is performed, the signal components distribute across multiple phase domains while DC offset remains concentrated, enabling accurate differentiation before the detection process begins.
2Reliability
If the frequency of the local oscillation signal is controlled to rotate the phase component, then the received signal and DC offset can be distinguished, but additional control mechanisms are required
Solution Approach 1:
The patent applies feedback by implementing a control loop where the controller monitors the phase rotation process and adjusts the local oscillator frequency accordingly. The controller receives information about the phase component rotation and provides feedback control to maintain the predetermined rotation speed. This feedback mechanism ensures that the phase rotation remains stable and controlled, enabling reliable DC offset detection while managing the complexity through automated closed-loop control rather than manual adjustment.
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 effectively suppresses signal receiving performance deterioration by correcting DC offset and preventing false operations, ensuring accurate FM detection even when the received signal is unmodulated and has the same frequency as the local oscillation signal, thereby enhancing the overall signal reception quality.
Implementation Method 1
a quadrature detector that performs a quadrature detection on the FM signal based on the local oscillation signal output by the local oscillator, and outputs an I-phase baseband signal and a Q-phase baseband signal
Data Source
AI summary
A quadrature detector performs a quadrature detection on an FM signal based on a local oscillation signal, and outputs a baseband signal. A first corrector and a second corrector perform a correction on the baseband signal based on a DC offset correction value. The DC offset detector performs a polar coordinate conversion on the baseband signal, and derives the DC offset value in such a way that respective amplitudes in a plurality of phase domains defined on an IQ plane approximate one another. An FM detector performs an FM detection on the corrected baseband signal, and generates a detection signal. A controller controls the frequency of the local oscillation signal in such a way that a phase component having undergone the polar coordinate conversion by the DC offset detector is rotated.