radio frequency circuit for contactless ic card

Abstract

The invention discloses a radio frequency circuit used for non-contact IC card. The radio frequency circuit adopts a variable-bandwidth amplitude-limiting circuit whose bandwidth is far lower than a modulation signal in a demodulation stage; and when a load modulation stage is entered or other high power operation is performed, bandwidth of the variable-bandwidth amplitude-limiting circuit is configured to be higher than a load current change frequency, an amplitude change of a carrier wave can be quickly tracked, and thus maximum load current is guaranteed to be provided. The radio frequency circuit used for the non-contact IC card can relatively remarkably improve a current load capability and working distance of the non-contact IC card.

Description

Technical field [0001] The present invention relates to the field of radio frequency technology, in particular to a radio frequency circuit used in a contactless IC (Integrated Circuit) card. Background technique [0002] Traditional non-contact IC card radio frequency circuit such as figure 1 Shown in the dashed box. This kind of radio frequency circuit has a problem: because the non-contact IC card communicates with the card reader through amplitude modulation, the amplitude limiter circuit will essentially limit the amplitude change; in order to ensure that the limiter circuit will not affect the solution of the non-contact IC card Harmonic modulation generally requires the limiting circuit to be designed as a low-pass circuit, with the highest cut-off frequency much lower than the signal frequency, and it cannot respond to rapid changes in the carrier amplitude. When entering the load modulation stage or performing other high-power operations, the average signal amplitude of...

AI Technical Summary

Problems solved by technology

There is a problem with this kind of radio frequency circuit: Since the non-contact IC card communicates with the card reader through amplitude modulation, the limiter circuit will essentially limit the change of the amplitude; in order to ensure that the limiter circuit will not affect the solution of the non-contact IC card Harmonic modulation generally requires the limiting circuit to be designed as a low-pass circuit, the highest cut-off frequency is much lower than the signal frequency, and cannot respond to rapid changes in carrier amplitude

When entering the load modulation stage or performing other high-power operations, the average signal amplitude of the carrier will become smaller, but because the limiter circuit cannot quickly track the change of the carrier amplitude, on the one hand, the current load capacity of the RF (radio frequency) circuit will decrease. On the other hand, the limiter circuit continues to discharge the unreasonable current

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