MI Sensor Antenna Synchronous Detection Circuit Noise Reduction
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Solution Overview
Problem
Existing antenna circuits using magneto-impedance sensors lack sensitivity to detect magnetic fields effectively, resulting in poor reception of radio-frequency signals, particularly due to high noise levels and difficulty in synchronizing signals for accurate side band detection.
Innovation Solution
The implementation of a synchronous detection circuit with a magnetic field detecting unit that reduces noise by inverting and adjusting the radio-frequency signal, allowing for improved detection of side bands and enhanced sensitivity through the use of a resonant circuit to isolate specific frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetic sensor using a magneto-impedance element is used to form an antenna, then the antenna can detect magnetic field changes, but the sensitivity is insufficient and noise levels are high
Solution Approach 1:
The patent introduces a synchronous detection circuit as an intermediary between the magnetic sensor and the output. This circuit uses a reference signal at the same frequency as the input signal to selectively amplify only the signal components that are synchronous with the reference, effectively filtering out noise while enhancing the desired magnetic field detection signal.
Solution Approach 2:
The synchronous detection circuit employs feedback mechanisms where the reference signal is continuously compared with the detected signal. The circuit adjusts the detection parameters based on the phase and amplitude relationship between the reference and input signals, optimizing the signal-to-noise ratio through continuous feedback control.
2Measurement precision
If a filter circuit is added after the antenna circuit to detect side bands, then magnetic field change detection is improved, but the circuit complexity increases
Solution Approach 1:
The patent combines the filter circuit and synchronous detection circuit into an integrated detection system. The filter circuit selectively passes side band frequencies while the synchronous detection circuit simultaneously performs phase-sensitive detection, merging multiple functions into a unified circuit architecture that reduces overall complexity compared to separate independent circuits.
Solution Approach 2:
The synchronous detection circuit serves multiple functions: it acts as a filter for specific frequencies, an amplifier for weak signals, and a phase detector. This multi-functionality eliminates the need for separate dedicated circuits for each function, thereby reducing overall circuit complexity while maintaining high detection accuracy.
3Power
If the radio-frequency signal level is high, then the signal can be detected, but the side bands become extremely small and difficult to detect
Solution Approach 1:
The synchronous detection circuit acts as an intermediary that selectively extracts side band information from the modulated signal. By using a reference signal and performing phase-sensitive detection, it isolates the small side band components from the dominant carrier signal, making them detectable even when the carrier power is high.
Solution Approach 2:
The patent changes the detection parameter from direct amplitude measurement to phase-sensitive detection. By measuring the phase relationship between the reference signal and the input signal, the system can detect small side band variations that would be imperceptible in the presence of a strong carrier signal.
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 the sensitivity of the antenna circuit, enabling more accurate detection of magnetic field changes and improving the reception of radio-frequency signals by reducing noise and isolating specific frequency components, thus improving the overall performance of the antenna system.
Implementation Method 1
the magneto-impedance effect represents an effect that impedance of soft magnetic material changes sensitively when external magnetic field is applied thereto so that output voltage across the soft magnetic material changes
Implementation Method 2
a resonant circuit connected with the magnetic field detecting circuit are included, a magnetic field change of a predetermined frequency is retrieved as an electric signal from a magnetic field change which is detectable by the magnetic field detecting element with a resonant effect of the resonant circuit
Implementation Method 3
The impedance change in the magnetic sensor modulates the signal of the radio-frequency signal generator S1. As shown in FIG. 20A, the signal of the radio-frequency signal generator S1 is modulated to be a state represented by reference numeral 2002 according to magnetic field change
Data Source
AI summary
The antenna circuit 42 includes: an MI magnetic sensor having an electric property which changes in accordance with a magnetic field change; a radio-frequency signal generator S1 to apply a radio-frequency signal to the MI magnetic sensor Z1; an inverter 92 to invert the radio-frequency signal; an adder 94 to reduce the radio-frequency signal by adding the inverted signal with a received signal obtained by the MI magnetic sensor Z1; and detectors D1 and D2 to detect the received signal in which the radio-frequency signal has been reduced. Further, included are a resonant circuit 620 including a magnetic sensor circuit Z1 and a resonant element such as quartz to retrieve a magnetic field change of a resonant frequency from a detected magnetic field change; and a resistance R0. Further, the magnetic sensor circuit 610 includes a magnetoresistance element 612, a DC power source 611 and a resistance R1.