Demodulation circuit for amplitude keying modulation signals

Abstract

The invention discloses a demodulation circuit for amplitude keying modulation signals. The demodulation circuit comprises a rectification circuit, a hysteresis comparator CMP1, a resistor R1, a resistor R2, a resistor R3, a metal oxide semiconductor (MOS) transistor M1, an MOS transistor M2, an MOS transistor M3, an MOS transistor M4, an MOS transistor M5, an MOS transistor M6, a capacitor C1 and a capacitor C2 which form a structure of two MOS transistor strings. A variable resistor formed by the two MOS transistor strings in the demodulation circuit can adjust the level of a signal input to the hysteresis comparator under the condition of high field intensity, so that the hysteresis comparator works in a normal state all the time; therefore, the demodulation circuit is ensured to work well in an overall dynamic range.

Description

technical field [0001] The invention relates to a demodulation circuit of an amplitude keying (ASK) modulation signal. Background technique [0002] In recent years, with the expansion of the application of contactless radio frequency cards compatible with ISO-14443TYPE A, more and more fields have begun to use this type of contactless radio frequency cards, such as access control, micropayment, transportation, souvenirs, etc. Due to the expansion of the application field, the use environment of the card has also become diversified. Various card readers and application environments have put forward high requirements for the compatibility of the card. This requirement is transformed from the perspective of chip design. The requirements for chip analog front-end design include requirements for chip port characteristics, power-on reset level, rectified voltage stability, clock extraction capability, signal demodulation capability, return modulation depth and many other requirem...

AI Technical Summary

Problems solved by technology

This kind of circuit has the advantages of simple structure, low power consumption, high demodulation sensitivity, and easy integration, etc., but the defect is that under the condition of large magnetic field, the demodulation circuit will have a serious decrease in sensitivity or even fail to demodulate.

However, in the current market applications, many card readers need to use very small transmitting coils due to space constraints or miniaturization, which will cause the magnetic field strength in the near-field area close to the antenna to reach a large value, thereby making the The card using the traditional R-C delay demodulation circuit cannot demodulate the signal of the card reader, which seriously affects the compatibility of the card.

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