METHOD FOR A BATTERY AND PASSIVE POWER SUPPLY TO AN RFID TAG AND A SWITCHING CIRCUIT FOR CARRYING OUT SAID METHOD

• US 20110241842A1
• Filed: 12/16/2009
• Published: 10/06/2011
• Est. Priority Date: 12/16/2008
• Status: Active Grant

• Current Assignee: ams R&D d.o.o. (Ams-Osram AG)
• Original Assignee: ams R&D d.o.o. (Ams-Osram AG)
• Inventors: Kovacic, Kosta, Pletersek, Anton, Vodopivec, Andrej
• Granted Patent: US 9,239,980 B2
• Time in Patent Office: Days
• US Class Current: 340/10.1
• CPC Class Codes: G06K 19/0702 the arrangement including a battery
• CPC Class Codes: G06K 19/0707 the arrangement being capable of collecting energy from external energy sources, e.g. thermocouples, vibration, electromagnetic radiation G06K19/0702 takes precedence
• CPC Class Codes: G06K 19/0712 the arrangement being capable of triggering distinct operating modes or functions dependent on the strength of an energy or interrogation field in the proximity of the record carrier active means for hindering electromagnetic reading or writing G06K19/07336
• CPC Class Codes: G06K 19/0717 the sensor being capable of sensing environmental conditions such as temperature history or pressure
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs

Abstract

A controlled switching circuit (csc) comprises two controlled switches (cs1, cs2) fabricated with PINTOS transistors and connected between its output terminal as well as a battery (b) or a rectifier rectifying voltage induced in an antenna. Conditions of the battery voltage and the rectified voltage with a time delay are checked. Only when the battery voltage gets unacceptable and the value of rectified voltage exceeded a preset value tag circuits are supplied by the rectified voltage induced in an antenna.

The invention provides for an automatic selection of a way of supplying an RFID tag in a way that it is stably supplied by a battery as far as still possible, but just according to the invention this is rendered possible for a longer time due to a very low voltage drop across a controlled switching circuit, and that a supply by a radio-frequency radiation field is selected only when the battery gets depleted.

Claims

1. A method for battery power supply and passive power supply to an RFID tag, which is provided with a battery (b) and situated in a radio-frequency radiation field, characterized in

that a value of a battery voltage (Vbat) is checked whenever the battery (b) is connected or

whenever a rectified voltage (Vrect) obtained by rectifying a voltage induced in an antenna (a) due to the radio-frequency radiation field reaches a preset value,

that, in case of an acceptable value of the battery voltage (Vbat),

circuits of the RFID tag are energized by the battery (b) through a controlled switching circuit (csc),

across which the battery voltage (Vbat) drops by a voltage drop across an open PMOS transistor,

and that, in case of an unacceptable value of the battery voltage (Vbat) and

after a termination of a time delay after the rectified voltage (Vrect)

obtained by rectifying the voltage induced in the antenna (a) due to the radio-frequency radiation field exceeded the preset value,

circuits of the RFID tag are energized by a rectifier rectifying said induced voltage through the controlled switching circuit (csc),

across which the output voltage (Vrect) of said rectifier drops by the voltage drop across the open PMOS transistor.

2. The method as recited in claim 1, characterized in

that said time delay extends between 5 microseconds and 500 microseconds.

3. The method as recited in claim 1, characterized in

that said time delay extends between 10 microseconds and 100 microseconds.

4. The method as recited in claim 2, characterized in

that said voltage drop across the open PMOS transistor amounts to several millivolts.

5. A switching circuit for battery power supply and passive power supply to an REID tag, which is provided with a battery (b) and situated in a radio-frequency radiation field,

characterized in

that it comprises a first controlled switch (cs1),

which is fabricated with a first PMOS transistor and

whose first terminal is connected to the energizing battery (b) having the voltage (Vbat) and

whose second terminal is connected to an output terminal (ps) of a controlled switching circuit (csc)

whereat there is a supply voltage (Vps), and

a second controlled switch (cs2),

which is fabricated with a second PMOS transistor and

whose first terminal is connected to a rectifier output terminal

whereat there is a rectified voltage (Vrect)

obtained by rectifying a voltage induced in an antenna (a) due to the radio-frequency radiation field and

whose second terminal is connected to an output terminal (ps) of the controlled switching circuit (csc),

that a signal (bat_OK) indicating good condition of said battery voltage (Vbat) and a time-delayed signal (rect_OK) indicating good condition of said rectified voltage (Vrect) are conducted to a logic decision circuit (ldc),

whose output signal causes a logic control circuit (lcc) either to close the first controlled switch (cs1) and to open the second controlled switch (cs2),

when the value of said battery voltage (Vbat) is acceptable, or to open the first controlled switch (cs1) and to close the second controlled switch (cs2),

when the value of said battery voltage (Vbat) is unacceptable and

the value of said rectified voltage (Vrect) exceeded a preset value,

and that a comparator circuit (cc) selects the higher between the battery voltage (Vbat) and said rectified voltage (Vrect) and said higher voltage being the highest voltage (Vmax) in the controlled switching circuit (csc)

is conducted through the logic control circuit (lcc) to bodies of the PMOS transistors of said first and second controlled switches (cs1, cs2).

6. The switching circuit as recited in claim 5, characterized in

that said time delay extends between 5 microseconds and 500 microseconds.

7. The switching circuit as recited in claim 5, characterized in

that said time delay extends between 10 microseconds and 100 microseconds.

8. The switching circuit as recited in claim 6, characterized in

that a dynamic-reset generator (drg) is connected to the output terminal (ps) of the controlled switching circuit (csc).