Voltage production circuit

Details Voltage production circuit Voltage production circuit

2001-12-27

2003-09-16

Berhane, Adolf D. (Department: 2838)

Electric power conversion systems

Current conversion

With voltage multiplication means

Reexamination Certificate

active

06621720

ABSTRACT:

FIELD OF THE INVENTION
The invention is related to the field of voltage production circuits, and, more particularly, to contactless chip cards or smart cards having an electrically erasable and programmable memory.
BACKGROUND OF THE INVENTION
FIG. 1
is a standard diagram of an integrated circuit for contactless smart cards. The integrated circuit comprises a detection circuit
10
, a rectifier circuit
20
, a filter
30
, a low-voltage regulation circuit
34
, modulation and demodulation circuits
36
, a logic circuit
38
and a memory
40
. The detection circuit
10
comprises a resonant circuit, including an antenna loop represented by the turns of a winding
11
, and a capacitor
12
. The elements
11
and
12
are parallel-connected. The rectifier circuit
20
comprises a four-diode bridge
21
and a capacitor
22
having one of its terminals connected to ground.
The filter
30
has a resistor
31
and a capacitor
32
. One of the terminals of the resistor
31
is connected to the common point
23
of one of the outputs of the bridge of diodes
21
and the capacitor
22
. Another terminal of the resistor
31
is connected to one of the terminals of the capacitor
32
and to an output
33
of the filter
30
. Another terminal of the capacitor
32
is connected to ground.
The low-voltage regulation circuit
34
comprises an input terminal connected to the output terminal
33
of the filter
30
and an output terminal
35
connected to the modulation and demodulation circuits
36
, the logic circuit
38
and the memory
40
. The modulation and demodulation circuits
36
comprise an input terminal connected to the common point
23
and an output terminal connected to the logic circuit
38
and the memory
40
. The low-voltage regulation circuit
34
as well as the modulation and demodulation circuits
36
are formed of transistors, resistors and capacitors in a conventional manner as would be appreciated by the skilled artisan.
In contactless smart cards, the data as well as the power received by the chip are transmitted by the reader in the form of an amplitude-modulated RF signal. The signal received by the card is detected and then rectified by the detection circuit
10
and the rectifier circuit
12
to give a rectified voltage HV
1
to the common point
23
. The mean amplitude of this rectified voltage HV
1
varies according to the mean power received by the card. This mean power depends mainly on the distance between the card and the reader. When the card is close to the reader, about a few centimeters, the amplitude of the rectified voltage HV
1
can thus reach 15-20 V, with an appropriate detection circuit.
The filter
30
lowers the level of the rectified voltage HV
1
. Then, through the regulation circuit
34
, a stable, DC low supply voltage V
cc
of about 4 V to 5 V is obtained at the output terminal
35
. The assembly formed by the detection circuit
10
and the rectification circuit
20
, the filter
30
and the low-voltage regulation circuit
34
is thus equivalent to a source of stable voltage that provides a low supply voltage V
cc
. This source of stable voltage supplies power to all the circuits of the smart card and especially the modulation and demodulation circuits
36
, the logic circuit
38
and the memory
40
. At the same time, the modulation and demodulation circuits
36
decode the voltage HV
1
and provide a binary signal DATA, containing the data transmitted to the card, the logic circuit
38
and the memory
40
.
The memory
40
is an electrically erasable and programmable memory, for example of the EEPROM type. It comprises a memory array
42
storing the data received by the card and a logic circuit
44
to control read and/or write operations in the memory array
42
. To carry out a write operation in the memory array
42
, it is necessary to have a voltage of about 16 to 18 V. For this, a voltage step-up circuit
46
provides a stable, DC high programming voltage HT from the low supply voltage V
cc
. The voltage step-up circuit
46
is, for example, of the charge pump type, and is made of capacitors, transistors and/or diodes according to known techniques.
The smart card receives a limited quantity of energy. Hence, a write operation is most usually performed alone in order to make the best possible use of the power received by the card. Nevertheless, to provide the high programming voltage HT, the charge pump consumes substantial current and hence a large quantity of energy. This causes an overload on the supply voltage source that gives the low voltage V
cc
. This overload could lead to a loss of the data received by the card, the erroneous storage of this data or else a break in communication between the reader and the smart card.
Moreover, a conventional charge pump takes up a large silicon surface area of up to 20% of the silicon surface area used for the memory. Indeed, the elements that form this charge pump, especially the capacitors and transistors, are bulky because their sizes are determined so that they can withstand high levels of voltage and power. Lastly, a charge pump is fragile, in particular because the capacitors forming it stand up rather poorly to excessively high voltages.
Given the characteristic disadvantages of the charge pump, it would therefore be worthwhile to eliminate it from a smart card memory, provided however that it is possible to have a stable, DC high voltage source, since this is indispensable for memory write operations.
SUMMARY OF THE INVENTION
An object of the invention is to provide an integrated circuit comprising a detection circuit and a rectifier circuit, series-connected to give a rectified voltage, and a low-voltage regulation circuit that receives the rectified voltage and gives a low supply voltage. According to the invention, the integrated circuit also comprises a voltage production circuit that receives the rectified voltage and produces a high voltage different from the low voltage. Thus, with the invention, the high voltage is no longer produced from the low supply voltage but directly from the rectified voltage, thus enabling the elimination of the charge pump commonly used.
The invention has the advantage of separating the voltage production circuit from the low voltage regulation circuit which provides the low supply voltage and from the circuits that are connected to it. Any malfunction in these circuits, due to the overloading of the low-voltage regulation circuit, is thus avoided. The transfer of data between the reader and the card is also avoided since the transfer is managed solely by the modulation and demodulation circuit and the logic circuit.
Furthermore, the voltage production circuit of the invention is far smaller and less fragile, and consumes far less energy than a charge pump as will be seen more clearly here below. Finally, by eliminating the charge pump commonly used in the memories, the invention provides for considerable savings in silicon surface area. This advantage is particularly valuable for applications such as electronic labels which require smaller circuits. According to one use of the invention, the integrated circuit also comprises a memory comprising a memory array, the memory array receiving the low voltage and the high voltage. The memory array is thus powered directly by the voltage production circuit and no longer by a charge pump internal to the memory.
According to one embodiment of the invention, the voltage production circuit is simply a wire. This embodiment is particularly simple to implement and it may be sufficient if the integrated circuit is used always at the same distance, of some centimeters, from the reader. In this case, the variation in the amplitude of the rectified voltage is fairly small.
According to another embodiment, the voltage production circuit comprises a controlled switch that is closed when it receives an active control signal (WRITE), and open otherwise. The control signal (WRITE) is for example a signal given by the logic circuit of the memory, if this logic circuit exists, or else by any other logic circuit of the int

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