Double Frequency Conversion Circuit for RF SIM Card Image Rejection
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Solution Overview
Problem
Existing radio-frequency SIM cards operating in the 2.4 GHz ISM frequency band require external image rejection filters and have high power consumption due to image rejection issues, which are not effectively addressed by existing frequency conversion technologies.
Innovation Solution
A double frequency-conversion circuit and method for radio-frequency SIM cards, incorporating a low-noise amplifier, high-medium-frequency mixer, low-medium-frequency mixer, local oscillator, quadrature I/Q circuit, and frequency divider, which generates a high-local-oscillation signal that is frequency divided and processed to achieve double frequency conversion without the need for an external image rejection filter, reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external image rejection filter is used in 2.4 GHz ISM frequency band, then image rejection problem is solved, but device complexity and power consumption increase
Solution Approach 1:
The patent extracts the image rejection function from external filters and implements it internally through frequency translation. By shifting the image frequency to 3 GHz band through double frequency conversion, the harmful image signal is separated from the 2.4 GHz working band, eliminating the need for external image rejection filters while maintaining reliable operation.
Solution Approach 2:
The patent changes the frequency parameters through double frequency conversion. The first mixer converts the 2.4 GHz RF signal to an intermediate frequency, and the second mixer converts it to baseband, while the image frequency is translated to approximately 3 GHz. This parameter transformation resolves the image rejection problem without requiring additional external filtering components.
2Reliability
If external image rejection filter is used, then image rejection is achieved, but power consumption increases
Solution Approach 1:
The patent removes the power-consuming external filter component from the system architecture and replaces it with frequency conversion circuitry that achieves image rejection through frequency translation to 3 GHz band, thereby reducing overall power consumption while maintaining image rejection capability.
Solution Approach 2:
The patent substitutes passive filter components with active frequency conversion mechanisms. By using mixers and local oscillators to translate frequencies, the system replaces the need for power-consuming external filters with a more energy-efficient frequency-based solution that achieves the same image rejection function.
3Device complexity
If single frequency conversion is used, then device complexity is reduced, but image rejection problem persists
Solution Approach 1:
The patent segments the frequency conversion process into two distinct stages: first mixing 2.4 GHz RF to intermediate frequency, then mixing intermediate frequency to baseband. This segmentation allows the image frequency to be translated to 3 GHz band in the first stage, achieving reliable image rejection while keeping each conversion stage relatively simple.
Solution Approach 2:
The patent adds a frequency dimension by translating the image signal to a different frequency band (3 GHz) through double frequency conversion. This dimensional transformation in the frequency domain resolves the image rejection problem without requiring complex filtering in the time domain, effectively solving the contradiction between simplicity and reliability.
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 solution effectively improves signal image frequency to approximately 3 GHz, eliminating the need for external image rejection filters and reducing power consumption, thereby addressing image rejection problems and enhancing operational efficiency in the 2.4 GHz ISM frequency band.
Implementation Method 1
a frequency divider, which performs N frequency dividing to a high-local-oscillation signal generated by the local oscillator to obtain a low-local-oscillation signal, N being a positive integer
Implementation Method 2
a high-medium-frequency mixer, a low-medium-frequency mixer... the antenna signal frf, after being amplified by the low-noise amplifier, is outputted to the high-medium-frequency mixer for mixing, to obtain a high-medium-frequency signal IFH
Data Source
AI summary
A double frequency-conversion receiving circuit used for a radio-frequency SIM card, including a low-noise amplifier (01), a high-medium-frequency mixer (02), a low-medium-frequency mixer (03), a local oscillator (04), a quadrature I/Q circuit (05), and a low-medium-frequency processing circuit (07), characterized in that it also includes a frequency divider (06) that performs N frequency dividing to a high-local-oscillation signal generated by the local oscillator (04), wherein the divided low-local-oscillation signal is inputted into the quadrature I/Q circuit (05), the outputted I/Q local-oscillation signal is inputted into the low-medium-frequency mixer (03) to obtain, after mixing, a low-medium-frequency signal, and the low-medium-frequency signal is further processed by the low-medium-frequency processing circuit (07) to output the signal needed, which has gone through the double frequency-conversion. The scheme described in this invention can improve the signal image frequency to approximately 3 GHz through smart frequency distribution without using an external image rejection filter. This effectively solves the image rejection problem when the radio-frequency SIM card is used in the 2.4 GHz ISM frequency band, and reduces power consumption of the chip.