FR2807585A1 - Integrated circuit on tele-supplied non contact 'smart' card, electronic label or badge has rectifier circuit including two MOS N and P transistor invertors - Google Patents

Abstract

The integrated circuit (13) includes a rectifier (3), connected to output terminals (A,B) of an oscillator (2), to supply a constant voltage between first and second supply lines (L1,L2), between which is logic circuits (1). The rectifier includes two MOS N and P transistor inverters (IV1,IV2) connected between the first and second supply lines and linking the input and output (A,B) of the oscillating circuit. Each inverter (IV1) includes a P type MOS transistor (M2) and an N type MOS transistor (M0) connected in series between the lines (L1,L2). The transistor grids are commoned on the terminal (A) of the resonant circuit, their drains are commoned on the other terminal (B). An isolation circuit (4) is connected between the first line (L1) and a corresponding input (Vdd) on the logic circuit (1). A filter circuit is connected between the lines (L1,L2) behind the isolation circuit.

Description

The present invention relates to a rectifier device in a remotely powered integrated circuit. It relates to all the fields where the integrated circuits are supplied by means of an electromagnetic field emitted by a system external to the circuit.

It applies in particular to contactless smart cards and electronic labels or badges.

In such applications, an oscillating circuit, of the LC type for example, is used for the regeneration of the power supply and the data transmission between the card and the reader. The oscillating circuit can be partially or completely integrated into the integrated circuit, or offset to the outside.

The oscillating circuit placed in an electromagnetic field delivers on its terminals, an alternating signal the same frequency as the signal emitted by the reader. The amplitude of this voltage signal is maximum when the natural resonance frequency of the oscillating circuit is equal to the transmission frequency of the reader.

An integrated circuit for such applications usually includes a circuit for rectifying the alternating signal supplied by the oscillating circuit. The function of the rectifier circuit is to connect this alternating voltage to a continuous load, corresponding to the load of the logic circuitry of the integrated circuit. In other words, this rectifier circuit converts the AC supply voltage into a DC supply voltage for the logic circuitry of the integrated circuit. This DC voltage is not constant, but contains an AC component (ripple) which is superimposed on a DC component (medium level).

A conventional embodiment of a rectifier circuit uses diodes, in an assembly can be simple, full wave, or other.

A well-known example of embodiment of a full-wave, or two-way rectifier circuit is shown in FIG. 1. In this example, the logic circuit 1 to be supplied is represented by equivalent load, typically a resistor Re in parallel on a Ce capacitor.

The rectifier circuit 3 is connected to the output pads A and B of an LC type oscillating circuit.

The rectifier circuit comprises a first diode D1 whose anode is connected to the pad and the cathode on a first supply line; a second diode D2, the cathode of which is connected to pad A and the anode to a second supply line, a third diode D3, the anode of which is connected to pad B, the cathode on the first supply line; and fourth diode D4 including the cathode connected to pad B and the anode to the second supply line. Thus, the two connected cathode diodes D1 and D3 supply the load and the two connected anode diodes D2 and D4 bring the load current to the other supply line. The first channel of this rectifier circuit is thus formed by the pair of diodes D1, D4 and the second channel is formed by the pair D2, D3. In applications of the contactless smart card or electronic label type, the signal level that is recovered from the pads A and the oscillating circuit is extremely variable, from zero to a few tens of volts, or even one hundred volts, depending on the applications. concerned. The signal level depends on many parameters, including the quality of the oscillating circuit, the intensity of the electromagnetic field, the surfaces of the transmitting and receiving antennas, the distance between the reader and the card.

As it is sought that the same integrated circuit can function in a wide range of applications, the rectifier circuit must therefore not only be able to detect the low levels, but also to limit the highest levels, so that the elements of the logic circuitry are not damaged. For this type of application, conventional diode rectifier circuits show poor performance. they lack sensitivity (detection.

low levels) and do not allow effective limitation of the average level of the DC voltage supplied at the output. The sensitivity of these rectifier circuits can be improved by using diode-mounted MOS transistors, which makes it possible to have a low diode detection threshold, equal to MOS transistor threshold voltage, but this is insufficient to obtain an effective limitation of the average level. voltage output. an additional specific limiting device must then be provided, which may conventionally include a zener diode or a large transistor upstream of the logic circuitry, capable of conducting a lot of current. This limiting device can be placed either directly on each of the output pads of the oscillating circuit, or in parallel on the electronic circuitry. Such additional devices represent an additional cost of silicon which is very troublesome for the intended applications.

An object of the invention is a rectifier circuit suitable for regenerating the supply of an electronic circuit from an electromagnetic field which does not have the above-mentioned drawbacks.

As claimed, the invention relates to a power regeneration device in a remotely powered integrated circuit. I1 comprises a rectifier circuit connected to the output pads of an oscillating circuit, to provide a level of DC voltage between a first and a second supply line, between which a logic circuitry of the integrated circuit is connected. According to the invention, the rectifier circuit includes two NP MOS transistor inverters, connected between the first and second supply lines and looped in input / output on the output pads of the oscillating circuit.

A rectifier circuit according to the invention limits by construction the voltage level of its inputs, that is to say on the inputs of the inverters. In this way the voltage level between the supply lines is also limited. In addition, a rectifier circuit according to the invention is effective even for low input levels, because the use of MOS transistor inverters makes it possible to obtain a low detection threshold. other characteristics and advantages of the invention are presented in the attached detailed description of an embodiment of the invention made by way of indication and limitation and with reference to the appended drawings in which - FIG. 1 already described represents a circuit integrated remotely powered comprising a rectifier circuit according to the state of the art; - Figure 2 shows a block diagram of a rectifier circuit according to the invention; - Figure 3 is a detailed embodiment of a rectifier circuit according to the invention; FIG. 4 shows the change in voltage on the output pad of the oscillating circuit, and FIG. 5 represents an electronic system using remotely powered integrated circuits. For the sake of simplicity, the elements common to the figures bear the same references.

As shown in FIG. 5, an electronic system 10 for a smart card, electronic label or badge type application comprises a reader 11 ensuring inter alia the remote supply of electronic label smart cards 12 by emission of an electromagnetic field B. These smart cards or electronic labels 12 include an integrated circuit of the remotely powered type 13.

This remotely powered integrated circuit 13 includes a power regeneration device.

A supply regeneration device 14 according to the invention is shown diagrammatically in FIG. 2. This device provides a level of direct voltage between a first supply line L1 and a second supply line L2, between which the circuitry electronics 1 of the integrated circuit is connected. The power regeneration device comprises an oscillating circuit 2, typically LC type followed by a rectifier circuit 3.

rectifier circuit 3 comprises two inverter transistors Mos N and P, denoted IV1 and IV2, looped in input / output between the pads A and B oscillating circuit 2. If one notes El and S1, the input and the output of 1 inverter IVl and E2 and S2, the input and output of the inverter IV2, the input E1 and the output S2 are connected together to pad A and the input E2 and output S1 are connected together to pad B.

In FIG. 3, an embodiment of the rectifier circuit according to the invention has been detailed. The inverter IV1 comprises a P-type MOS transistor, and an N-type MOS transistor, M0, connected in series between the first and second supply lines. Their grids connected in common form the input El, connected to the pad A. Their drains connected in common form the output S1, connected to the pad B.

'inverter IV2 comprises a P-type MOS transistor, M3 and an N-type MOS transistor, M1, connected in series between the first and second supply lines. Their grids connected in common form the input E2, connected to the pad B. Their drains connected in common form the output S2, connected to the pad A.

The inverters IV1 and IV2 are therefore looped back into input / output between the output pads and B of the oscillating circuit and connected between the two supply lines L1 and L2 in accordance with the principle of the invention. As the output pads A and B of the oscillating circuit correspond inputs or outputs of the inverters IV1 and IV2, the variation of the voltage level on these pads A and B results in a modification of the conduction states of the transistors in the inverters IV1 and IV2. Thus, depending on the voltage levels present on the pads A and B and on the supply lines L1 and L2, one goes through different operating modes of the transistors of the inverters. Depending on the operating modes, the drains of the inverter transistors are brought to a level corresponding to their sources, thus ensuring the regeneration of the supplies on the supply lines L1 and L2, or, conversely, the sources of the inverter transistors are brought to a level corresponding to their drains, thereby limiting the voltage excursion on the output pads A and B of the oscillating circuit.

Let us detail the operation of the rectifier circuit according to the invention. In FIG. 4, an alternative signal representing the evolution over time of the potential at pad A has been shown, as well as the average level Vdb of regenerated voltage on the first voltage line Ll and the average level Gnd of regenerated voltage on the second supply voltage line L2, with Vdb> Gnd. We denote VA and the potential at plot A and at plot B.

Outside the electromagnetic field, the supply lines L1 and L2 are floating.

When the integrated circuit enters an electromagnetic field, as soon as the voltage difference between the two pads A and B of the oscillating circuit becomes greater than or equal to a threshold voltage (Vt of MOS transistor, the rectifier circuit 3 enters operation. a VA greater than VB, it is the transistors MO and M3 which start to drive. As drain of the MOS transistor M0, connected to the pad B, is low voltage level of the pad B (VA> VB), this transistor thus regenerates this level low voltage on its source, and therefore on the second supply line L2. As the drain of the MOS transistor M3 is at the high voltage level of the pad A, this transistor regenerates this high voltage level on its source, and therefore on the first supply line Ll.

If we have VB greater than VA, it is the transistors M1 and M2 which start to drive. As the drain of the MOS transistor M1, connected to the pad A, is at the voltage level of the pad A, this transistor thus regenerates low voltage level on its source, and therefore on the second supply line L2. As the drain of the MOS transistor M2 is at the high voltage level of the pad, this transistor regenerates this high voltage level at its source, and therefore on the first supply line L1.

The rectifier circuit according to the invention thus allows the regeneration of the power supplies, as soon as a potential difference equal to the threshold voltage of a MOS transistor is detected. There is thus a very sensitive rectifier circuit.

In addition, as long as the potential on one of the oscillating circuit pads is lower in absolute value than the regenerated voltage on one or the other supply line, the potential on the other pad of the oscillating circuit is limited by the circuit. rectifier, by feedback, so that the oscillation amplitude across the oscillating circuit is naturally limited. The more the mean level of the supply lines L1 and L2 increases, the more the operating zones of the rectifier circuit, for which the potential on the pads A and B is less than the regenerated voltage between the lines L1 and are extended. The operating area of the limiting rectifier therefore increases with the increase in the voltage level between the lines L1 and L2.

Thus, this limitation is particularly effective.

To explain this limitation in more detail, we base ourselves on Figure 4. In this figure, we consider that we are in steady state. The average voltage level Vdb and Gnd of the lines L1 and L2 has been shown. In practice, the actual tension on these lines fluctuates around these levels.

The regenerated voltage level on lines L1 and L2 is assumed to be constant.

If we take an operating zone Z1 in which the absolute voltage level VA is rising but lower than the regenerated voltage level on the first supply line L1. In this zone Z1, the transistor M2 tends to conduct in order to raise the voltage on its drain, connected to the pad B. Thus, the transistor M2 tends to brake the voltage drop on the pad B.

Thus, according to the absolute voltage levels on the pads A and B and on the supply lines L1 and L2, the transistors of the inverters will regenerate the voltage level Vdb on this line and / or limit the voltage excursion between the studs A and B.

Thus, the structure of the rectifier circuit with inverters with MOS N and P transistors looped allows regeneration of the power supplies with great sensitivity, while ensuring by construction the crushing of the voltage difference between the pads A and B of the oscillating circuit.

The voltage level obtained between the power supply lines of the electronic circuitry depends in practice on the equivalent load of this circuitry and on the dimensions of the transistors of the rectifier circuit. In practice, for example, it is possible to obtain between 4 and 7 volts DC voltage level between the two supply lines. Depending on the case, it may still be necessary to limit this voltage level to reduce it to less than 3 or 4 volts, but the limiting device is then very small in size.

In an improvement represented in FIG. 3, an isolation circuit 4 is provided between the rectifier circuit 3 and the electronic circuitry 1. In the example, and in a completely conventional manner, this isolation circuit is produced by a diode, connected between the first supply line L1 and the positive supply input Vdd of the electronic circuit 1.

In another improvement, a filtering circuit 5 is provided, to eliminate the residual AC component at the output of the rectifier circuit. This filtering circuit typically comprises a resistance Rd and a capacitor in parallel between the two supply lines and L2.

In the case where an isolation circuit 4 is provided, the filtering circuit is preferably connected upstream of the isolation diode.

Claims (7)

1. Power regeneration device in a remotely powered integrated circuit (13), comprising a rectifier circuit (3) connected to the output pads (A, of an oscillating circuit (2), to provide a DC voltage level between a first and a second supply line (L1, L2), between which a logic circuit (1) of the integrated circuit is connected, characterized in that said rectifier circuit comprises two inverters with MOS N and P transistors (IV1, IV2) connected between the first and second supply lines and looped in input / output on the output pads B) of the oscillating circuit. 2. Power regeneration device according to claim 1, characterized in that each inverter (IV1) comprises a P-type Mos transistor (M2) and an N-type MOS transistor (MO) connected in series between the two lines of supply (L1, L2), their grids being connected in common on a studs (A) of the resonant circuit, their drains being connected in common on the other stud (B). . 3. power regeneration device comprising a rectifier circuit according to claim 1 or 2, characterized in that it further comprises an isolation circuit (4) connected between the first supply line (L1) and an input power supply (Vdd) on the logic circuit). 4. Supply regeneration device according to claim 1 or 2, characterized in that it further comprises a filtering circuit of the residual alternating component, connected between the two supply lines (L1, L2). 5. Power regeneration device according to claim 4, comprising an insulation circuit (4) according to claim 3, characterized in that the filtering circuit is connected upstream of said isolation circuit. 6. Integrated circuit remotely powered for smart card or electronic label comprising a power regeneration device according to any preceding claim. 7. Electronic system comprising a reader ensuring the remote supply of smart cards or electronic labels according to claim 6