Modulation circuit with automatic load resistance adjustment function

Abstract

The invention provides a modulation circuit with an automatic load resistance adjustment function. The modulation circuit comprises an electromagnetic induction coupling circuit, a rectification circuit, an amplitude limiting circuit and a self-adjusting circuit. The electromagnetic induction coupling circuit comprises a first inductor, a second inductor and a first capacitor, wherein two ends ofthe first inductor are connected with an alternating current power supply, one end of the second inductor is connected with one end of the first capacitor, the other end of the second inductor is connected with the other end of the first capacitor, and the second inductor is connected with the first inductor through a mutual inductance coefficient. The NMOS transistors in the rectifying circuit and the amplitude limiting circuit are respectively and independently connected into a diode form, so that the mutual crosstalk among the rectifying circuit, the amplitude limiting circuit and the modulation circuit is reduced. Meanwhile, the NMOS transistor in the modulation circuit can be used for copying the current of the NMOS transistor in the amplitude limiting circuit in proportion, so that the static working power consumption of the modulation circuit can be reduced.

Description

technical field [0001] The invention belongs to the technical field of radio frequency identification in integrated circuits, and relates to a modulation circuit with automatic adjustment of load resistance. Background technique [0002] Radio frequency identification technology is a non-contact automatic identification technology (Radio Frequency Identification, RFID). Its basic principle is to use radio frequency signals to transmit data between readers and transponders to achieve target identification and information exchange. The load resistance (turned on or off) on the transponder antenna will cause the voltage change of the reader antenna, so as to realize the data transmission from the transponder to the reader. This data transmission method is called load modulation. Schematic diagram of the working principle of load modulation Such as figure 1 shown. [0003] Due to the weak coupling between the reader antenna and the transponder antenna, the useful signal voltag...

AI Technical Summary

Problems solved by technology

[0016] 1) When the transponder 120 is in weak magnetic field modulation, the modulation load resistance is relatively small, resulting in a relatively large amplitude of the modulation signal of the reader 110. At this time, there are more interference signals on the antenna of the reader 110, which is not conducive to signal demodulation ;

[0017] 2) When the transponder 120 is in weak field modulation, the energy obtained by the transponder 120 will be relatively small, and the modulation load resistance is also relatively small at this time, which will easily cause the power supply voltage of the transponder 120 to drop rapidly, and further cause the chip of the transponder 120 to work unusual;

[0018] 3) If the transponder 120 is modulated with a small load resistance, it is necessary to design a modulation load resistance with an excessively large area, which will cause the chip area to be too large and difficult to integrate

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