AM Receiver Quadrature Phase Correction Without Auxiliary Mixing
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Solution Overview
Problem
Conventional receivers face challenges in maintaining optimal reception quality due to parasitic direct current signals, which can cause phase control errors and interfere with the demodulation of amplitude-modulated signals, especially in direct conversion receivers where few oscillators are used, leading to potential interference and increased complexity.
Innovation Solution
A phase correcting device adjusts the phase of oscillator signals based on variations in the alternating current component of the quadrature mixer output signal, eliminating the need for auxiliary mixing signals and thereby reducing parasitic modulation, allowing for effective phase-error correction without introducing additional interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a mixer circuit is used for phase detection, then phase detection can be performed, but a parasitic direct current signal is generated that causes phase control errors and degrades reception quality
Solution Approach 1:
The patent extracts the parasitic direct current component from the mixer output signal and removes it before using the signal for phase detection. This is achieved by detecting the alternating current component that is synchronous with the auxiliary mixing signal and eliminating the parasitic DC offset, thereby preventing phase control errors while maintaining phase detection capability
Solution Approach 2:
The patent introduces an auxiliary mixing signal as an intermediary to modulate the phase-detection oscillator signal. This auxiliary signal serves as a mediator that enables the separation of the useful phase detection signal from the parasitic DC component, allowing for effective filtering and elimination of the harmful DC offset
2Object-affected harmful factors
If an auxiliary mixing signal is used to modulate the phase-detection oscillator signal, then the parasitic direct current signal can be eliminated, but the auxiliary mixing signal causes parasitic modulation of other oscillator signals and adversely affects reception quality
Solution Approach 1:
The patent converts the harmful effect of the auxiliary mixing signal by using it to generate a detectable alternating current component in the quadrature mixer output. This alternating current component, which would otherwise be useless, is now utilized as an indicator to control the phase-error corrector, thereby eliminating the parasitic DC signal without requiring the auxiliary signal to directly modulate other oscillators
3Reliability
If a phase-error corrector is introduced to correct quadrature phase errors, then reception quality can be improved, but the device complexity increases
Solution Approach 1:
The patent merges the phase-error correction function with the existing synchronization circuitry by integrating the phase-error corrector into the feedback loop of the phase-locked loop. The phase-error correction is combined with the automatic frequency control, allowing both functions to operate within a unified circuit architecture, thereby minimizing additional complexity
Solution Approach 2:
The phase-error corrector automatically adjusts the phase of the oscillator signals based on the detected alternating current component magnitude, without requiring external intervention. The system self-regulates by using the quadrature mixer output to control the phase correction, eliminating the need for complex external control mechanisms
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 enhances reception quality by accurately correcting quadrature phase errors, reducing the impact of parasitic direct current signals, and simplifying the receiver design, making it suitable for direct conversion receivers that are less sensitive to interference and cost-efficient.
Implementation Method 1
A quadrature mixer mixes the quadrature oscillator signal with the amplitude-modulated signal so as to obtain a quadrature mixer output signal
Data Source
AI summary
In a receiver, a synchronization circuit (MIX2, OSC, C1, R1) provides a set of oscillator signals (OSI, OSQ) that are synchronized with a carrier of an amplitude-modulated signal. The set of oscillator signals (OSI, OSQ) comprises a quadrature oscillator signal (OSQ), which is substantially 90° phase shifted with respect to the carrier of the amplitude-modulated signal. A quadrature mixer (MIX2) mixes the quadrature oscillator signal (OSQ) with the amplitude-modulated signal so as to obtain a quadrature mixer output signal (MO2a). A phase-error corrector (PEC) adjusts the phase of the oscillator signals in response to a variation in the magnitude of an alternating current component (AC) in the quadrature mixer output signal (MO2a).