Chip card with field strength detector having a switch and load to limit damping to the measurement cycle
First Claim
1. A contactless and batteryless chip card havingan antenna coil,a transmission and reception stage which via an electromagnetic alternating field generated by a write/read unit supplies the chip card with energy and ensures bidirectional data transmission to the write/read unit,a functional circuit part having a function which is dependent on an application of the chip card, anda detector for determining a field strength of said electromagnetic alternating field transmitting energy to said chip card, said detector having a switch and a load, said load being switched parallel to said coil by said switch for determining the field strength of the electromagnetic alternating field when a measurement cycle signal which is supplied to said switch is generated.
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Accused Products
Abstract
The invention relates to a contactless and batteryless chip card having an antenna coil, a transmission and reception stage which via an electromagnetic alternating field generated by a write/read unit on the one hand supplies the chip card with energy and on the other hand ensures bidirectional data transmission to the write/read unit. The chip card in accordance with the invention has a detector for determining the field strength of the electromagnetic alternating field transmitting energy to said chip card. The functions of the user part, which have a high energy requirement to implement them, are only implemented advantageously when the detector has detected a sufficient field strength. This prevents defective or incomplete implementation of energy-consuming functions of the chip card before they are begun. The field strength detector consists of a switch and load in parallel to the coil with the switch controlled by a control circuit to cause the switch to be on only during a measurement cycle. By having the switch on only during the measurement cycle damping of the coil is prevented and the range of the card is extended compared to a card where the load is always in parallel to the coil. The control circuit can also monitor the supply voltage and prevent the measurement cycle if the supply voltage drops below a predetermined value. Such interruption in the measurement cycle prevents the measurement from reducing the supply of energy to the rest of the circuits.
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Citations
17 Claims
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1. A contactless and batteryless chip card having
an antenna coil, a transmission and reception stage which via an electromagnetic alternating field generated by a write/read unit supplies the chip card with energy and ensures bidirectional data transmission to the write/read unit, a functional circuit part having a function which is dependent on an application of the chip card, and a detector for determining a field strength of said electromagnetic alternating field transmitting energy to said chip card, said detector having a switch and a load, said load being switched parallel to said coil by said switch for determining the field strength of the electromagnetic alternating field when a measurement cycle signal which is supplied to said switch is generated.
Specification