Harvester with an RFID modulator

Abstract

A harvester with an RFID modulator has two input terminals (RF1, RF2) and two output terminals (HRV, GND). The harvester comprises at least two stages (S1a, S2, S3), wherein a single stage (S2) comprises two capacitors (C1, C2) and two transistors (T1, T2), wherein a first capacitor (C1) is connected to the first input terminal (RF1) and a second capacitor (C2) is connected to the second input terminal (RF2). Transistors (T1, T2) are drain-connected and connected to the first capacitor (C1), wherein the first transistor (T1) is connected as a source to the input of a given stage (S2), and the second transistor (T2) is connected as its source to the second capacitor (C2) and to the output of the given stage (S2). The gate of one of the transistors (T1) in at least one harvester stage (S2) is connected to the source of the other transistor (T2) in the same stage, while the gate and drain of the other transistor (T2) in that stage are connected to each other.In at least one harvester stage (S1a), the gate of the first transistor (Tw) is connected to the input or output of this stage (S1a) via a modulating transistor, the gate of which is connected to the modulation input of the circuit (M). Furthermore, the gate of the first transistor (Tw) is also connected to the output of one of the harvester stages (S3) via a resistor (R) or via a current source transistor. The gate and drain of the second transistor in this stage (S1a) are connected together.

Description

[0001] RFID harvester with modulator

[0002] The invention concerns an RFID harvester with modulator intended especially for NFC circuits.

[0003] From the European invention EP4095754A1, there is known a radio frequency identification (RFID) tag. The RFID tag includes an antenna port to receive an input AC signal and a hybrid limiter including a clamping device configured to limit a voltage of the input AC signal to a preconfigured limit. The hybrid limiter is configured to provide a stable ground reference for the clamping device.

[0004] In particular, this invention is known for a solution of a harvester with modulator, in which the harvester in the form of a rectifier is connected in parallel with the modulator, and both of these circuits are connected to the inputs of the RFID tag.

[0005] From the German patent application DE102005032590A1, there is known an invention concerning a modulator used for data transmission between a transponder and a bases station, that can either modulate amplitude or phase of a carrier signal. The modulator comprises a control unit, a rectifier circuit for rectifying the carrier signal that has one or more rectifier stages, and at least a circuit device that can be controlled via the modulation control signal and which overrides, at its output side, at least one rectifier stage by acting upon at least one node of the rectifier stage with a reference voltage. The invention also relates to a transponder with an inventive modulator and an operating method for an inventive modulator.

[0006] In particular, a solution of a harvester with a modulator is known from this invention, in which the harvester in the form of a rectifier is built of stages, wherein one stage contains two capacitors connected to the input terminals of the circuit and two diodes connected to the capacitors and the input and output of the given stage. A switching device controlled by a modulation signal is connected to the terminals of one of the diodes in one of the stages, which synchronously connects the proper node to a reference potential, which additionally or alternatively causes amplitude keying of reflected waves. Two modes of operation are possible, i.e., amplitude keying and phase shift keying, which can be implemented simultaneously or, depending on the application, separately from each other.

[0007] It is known from the Chinese invention CN102104329A, a harvester in the form of a rectifier, which contains stages, whereas one stage contains two capacitors connected to the input terminals of the circuit and two diodes connected to the capacitors and the input and output of a given step.

[0008] From the American patent US7167090B1, there is known a harvester in the form of a rectifier and a charge pump, in which the charge pump stage includes two capacitors and four transistors connected to the capacitors and inputs and outputs of this stage, wherein the gates of the transistors being connected to the drains or sources of other transistors.

[0009] In the state-of-the-art, especially in electronics engineering, there are known (remote) radio-frequency identification (RFID) systems, and in particular near-field communication (NFC). There are known in the art field-effect transistors (FETs) with an insulated gate, thin-film transistors (TFTs), as well as transistors based on indium-gallium zinc oxide (IGZO or InGaZnO - from: indium (In), gallium (Ga), zinc (Zn), oxygen (O)). It is also known that the designation of the drain and source of these transistors is conventional, because due to the symmetrical structure of the transistor, changing these designations does not affect the functionality of the transistor or the circuit in which it is located; however, this nomenclature is of an ordering nature.

[0010] The aim of the invention is to create a harvester circuit with a modulator that will solve the problem of simultaneously effectively obtaining power while performing modulation with given parameters.

[0011] In an RFID harvester with modulator, having two input terminals and two output terminals, the harvester comprises at least two stages, wherein a single stage comprises two capacitors and two transistors, where a first capacitor is connected to the first input terminal and the second capacitor is connected to the second input terminal, and the drains of the transistors are connected together and connected to the first capacitor, wherein the source of the first transistor is connected to the input of a given stage, and the source of the second transistor is connected to the second capacitor and to the output of a given stage, according to the invention, the gate of one of the transistors in at least one stage of the harvester is connected to the source of a second transistor in the same stage, while the gate and the drain of the second transistor in this stage are connected together. Furthermore, in at least one harvester stage, the gate of the first transistor is connected to either the input or the output of this stage through a modulation transistor, the gate of which is connected to the modulation input of the circuit. The gate and the drain of the second transistor in this stage are connected to each other, whereas the gate of the first transistor is also connected to an output of one of the harvester stages through either a resistor or a transistor having its gate connected to its drain constituting a current source.

[0012] The technical advantages of this solution are as follows. By connecting the gate and drain of the transistor, it acts as a diode. By connecting the gate of one of the transistors to the source of the other transistor within one stage, the voltage on the gate of the transistor is boosted, providing better performance than a diode due to faster switching. By using a modulation transistor, the energy efficiency of the harvester can be controlled. By using a resistor or a current source, the initial polarization of the transistor of a given stage is obtained.

[0013] Advantageously, the input of the first stage is connected to the second input terminal. Therefore, the first stage of the entire cascade is connected to one of the input terminals providing power supply of the circuit. Advantageously, the second input terminal simultaneously constitutes the ground of the entire RFID circuit. Therefore, all RFID circuits can operate on a typical reference, which is delivered the ground potential.

[0014] Advantageously, the RFID harvester with modulator operates substantially at a frequency of 13.56 MHz of the input signal. For that reason, it is possible to use the circuit to implement the NFC standard.

[0015] Advantageously, between the first input terminal and the first output terminal a diode is connected, formed from the transistor channel, in which a gate is connected to the first input terminal. For that reason, the function of a bypass diode is implemented, which shortens the switch-on time of the circuit connected to the harvester output.

[0016] Advantageously, the RFID harvester with modulator has 3 or 4 stages. Three stages provide relatively higher circuit efficiency, while four provide a higher harvester output voltage.

[0017] Advantageously, the resistor is connected to the output of the last or one before the last stage of the harvester. As a result of the connection to the last stage, the modulation coefficient has the highest value. In contrast, when connected to the penultimate stage, the rectifier opening angle is relatively smaller and therefore, the power losses are relatively lower.

[0018] Advantageously, the transistor constituting the current source is connected to the output of the last or one before the last stage of the harvester. As a result of the connection to the last stage, the modulation coefficient has the highest value, whereas when connected to the preceding stage, the opening angle is relatively smaller and therefore, the power losses are relatively lower.

[0019] Advantageously, all transistors in the circuit are the FETs of "n" type. The use of one type of FETs with insulated gates simplifies the technological process of implementing a circuit.

[0020] Advantageously, all transistors in the circuit are TFT-type transistors. TFTs allow to manufacture cheap and / or flexible integrated circuits.

[0021] Advantageously, the transistor channels are made of amorphous semiconductor material. The use of amorphous semiconductor material ensures low cost of manufacturing transistors (at relatively low temperatures).

[0022] Advantageously, the transistors contain indium-gallium zinc oxide. Using indium gallium zinc oxide (IGZO) provides a relatively high carrier mobility parameter.

[0023] Advantageously, the channel lengths of the transistors used in the harvester stages range from 400 to 1000 nm. For that reason, it is possible to obtain the operating frequency of the circuit that is typical for NFC.

[0024] Advantageously, the width-to-length ratio of transistor channels used in the harvester stages ranges from 100 to 300. By providing such a high W / L ratio of transistors, especially when their channels are technologically of the minimum length, it is possible to obtain sufficient power for the entire RFID circuit.

[0025] Advantageously, the width-to-length ratio of the modulation transistor channel ranges from 20 to 50. For that reason, the current efficiency of the modulating transistor, especially when its channel is of technologically minimal length, is adequate to drive a gate of a transistor to which the modulating transistor is connected. Advantageously, the width-to-length ratio of the transistor channel constituting the current source ranges from 0.1 to 0.5. Due to the significant extension of the transistor channel length, especially when its channel is of technologically minimal width, low sensitivity of the transistor current to the gate-source voltage of the current source is ensured.

[0026] Advantageously, the capacitances used in the harvester stages range from 30 to 80 pF. Therefore, the harvester can store enough energy to power the entire RFID circuit.

[0027] Advantageously, the ratio of the capacitance of capacitors used in the first harvester stage to the capacitance of capacitors used in the remaining harvester stages is 1 to 3. Increasing the capacitance of the first stage capacitors provides better ripple rejection during modulation.

[0028] The invention has been described below in detail, with reference to the attached figures. Fig. 1 presents a schematic diagram of a three-stage RFID harvester with modulator, and Fig. 2 - a schematic diagram of a four-stage RFID harvester with modulator.

[0029] RFID harvester with modulator in the embodiment shown in Fig. 1 comprises two input terminals RF1 and RF2, and two output terminals HRV and GND, between which there are three harvester stages Sla, S2 and S3. Each stage’s basic, essential structure is presented in the second stage S2, which comprises two capacitors Cl and C2, and two transistors T1 and T2. The first capacitor Cl is connected to the first input terminal RF1, and the second capacitor C2 is connected to the second input terminal RF2. Both transistors T1 and T2 have drains connected and connected to the first capacitor Cl. The source of the first transistor T1 is connected to the input of the second stage S2. The source of the second transistor T2 is connected to the second capacitor C2 and to the output of second stage S2. The gate of the first transistor T1 is connected to the source of the second transistor T2, while the gate and the drain of the second transistor T2 are connected forming a diode.

[0030] The construction of the first stage Sla of the RFID harvester with modulator corresponds to the construction of the second stage S2, with the difference that the gate of the first transistor Tw of this stage is connected to the source of the second transistor in the same stage through a modulation transistor Tma. Additionally, the gate of the transistor connected to the modulation transistor Tma is also connected to the output of the third stage of the harvester S3 through a resistor R. Nevertheless, the gate of the modulation transistor Tma is connected to the modulation input of the circuit M.

[0031] The structure of the third stage S3 of the RFID harvester with modulator essentially corresponds to the structure of the second stage S2, with the difference that a transistor Td is connected between the first input terminal RF1 and the first output terminal HRV, and the gate of the transistor is connected to the first input terminal RF1, forming a bypass diode.

[0032] RFID harvester with modulator in the embodiment shown in Fig. 2 comprises two input terminals RF1 and RF2, and two output terminals HRV and GND, between which there are four harvester stages Sib, S2, S3, and S4. Each stage's basic, essential structure is presented in the second stage S2, which comprises two capacitors Cl and C2, and two transistors T1 and T2. The first capacitor Cl is connected to the first input terminal RF1, and the second capacitor C2 is connected to the second input terminal RF2. Both transistors T1 and T2 have drains connected and connected to the first capacitor Cl. The source of the first transistor T1 is connected to the input of the second stage S2. The source of the second transistor T2 is connected to the second capacitor C2 and to the output of second stage S2. The gate of the first transistor T1 is connected to the source of the second transistor T2, whereas the gate and the drain of the second transistor T2 are connected together to form a diode.

[0033] The construction of the first stage Sib of the RFID harvester with the modulator basically corresponds to the construction of the second stage S2, with the difference that the gate of the first transistor Tw of this stage is connected to the second input terminal RF2 through a modulation transistor Tmb and to the source of transistor Tz, which is connected to the output of the third stage of the harvester S3. The gate and the drain of this transistor Tz are connected, and therefore, the transistor Tz, with a suitably long channel, acts as a current source in the circuit. Nevertheless, the gate of the modulation transistor Tmb is connected to the modulation input of the circuit M. Due to the significant Tz transistor channel length extension, especially when its channel is technologically of minimal width, a low sensitivity of the transistor current to the gate-source voltage of the current source is ensured.

[0034] The structure of the third stage S3 of the RFID harvester with a modulator is identical to that of the second stage S2 of the harvester.

[0035] The structure of the fourth stage S4 of the RFID harvester with the modulator essentially corresponds to the structure of the second stage S2, with the difference that a transistor Td is connected between the first input terminal RF1 and the first output terminal HRV, and the gate of the transistor is connected to the first input terminal RF1, forming a bypass diode.

[0036] The operating principle of the harvesters in the presented embodiments is as follows. The connection of an NFC antenna to the RF1 and RF2 harvester inputs allows for obtaining energy from the RF signal, which is then transmitted to subsequent analog subsystems such as: a carrier frequency divider or an AM demodulator. The entire RFID tag circuit can be powered from a single harvester, which acts both as a rectifier and a voltage multiplier of a carrier signal, where the carrier frequency for NFC is 13.56 MHz. The voltage from the harvester usually ranges from 2.5 V to 5 V - depending on the antenna’s proximity to the signal source, the modulation depth of the NFC reader, and the momentary power dissipation of the tag. Combining the harvester and the modulator functionalities allows for reducing the footprint and the total power dissipation. In this solution, the momentary harvester efficiency depends on a digital signal at the modulation input M. Therefore, the change in the voltage at this input M affects the momentary voltage multiplication factor and, thus, the momentary antenna current flow and the resultant output voltage. This technique ensures the proper AM modulation level (>10%) and eliminates the need for the use of an additional modulator circuit. An internal response circuit of the NFC tag provides an encoded message, affecting the harvester by the modulation signal.

[0037] The harvesters in the presented embodiments consist of three or four half-sinewave voltage multiplying stages and a bypass diode made of a Td transistor that reduces the power-up time. The minimum RF signal amplitude ensuring the circuit operation is strictly related to the threshold voltage parameter of the transistors. However, the proper minimum is assumed to be 1.8 V. The logical ‘ 1’ applied to the modulation input M reduces the gate- source voltage of Tw with a transistor key. The effective conduction angle of the Tw diode drops. The opposite logical state at the modulation input M (i.e., the logical ‘0’) increases the conduction angle of Tw, leading to lower circuit efficiency and a higher momentary current flow through the tag, and reader antennas. This way a sufficient AM modulation factor is obtained, which reaches or even exceeds 10% required by the NFC Type-1 standard.

[0038] The invention allows the antenna's RF signal to be obtained efficiently enough to power all subsequent subsystems of the RFID tag, and to modulate the signal, providing return communication from the tag. The industrial application of the invention is in the industry and the market of products requiring individual electronic markings.

Claims

Claims1. An RFID harvester with modulator having two input terminals (RF 1 , RF2) and two output terminals (HRV, GND), in which the harvester comprises at least two stages (SI a, Sib, S2, S3, S4), wherein a single stage (S2) comprises two capacitors (Cl, C2) and two transistors (Tl, T2), where the first capacitor (Cl) is connected to the first input terminal (RF1), and the second capacitor (C2) is connected to the second input terminal (RF2), and the drains of the transistors (Tl, T2) are connected together and connected to the first capacitor (Cl), wherein the source of the first transistor (Tl) is connected to the input of a given stage (S2), and the source of the second transistor (T2) is connected to the second capacitor (C2) and to the output of a given stage (S2), characterized in that the gate of one of the transistors (Tl) in at least one stage of the harvester (S2) is connected to the source of a second transistor (T2) in the same stage, while the gate and the drain of the second transistor (T2) in this stage are connected together, and in that in at least one harvester stage (SI a, Sib) the gate of the first transistor (Tw) is connected to either the input or the output of this stage (SI a, Sib) through a modulation transistor (Tma, Tmb), the gate of which is connected to the modulation input of the circuit (M), while the gate and the drain of the second transistor in this stage (SI a, Sib) are connected to each other, furthermore the gate of the first transistor (Tw) is also connected to an output of one of the harvester stages (S3) through either a resistor (R) or a transistor having its gate connected to its drain (Tz) constituting a current source.

2. The RFID harvester with modulator according to claim 1, characterized in that the input of the first stage is connected to the second input terminal (RF2).

3. The RFID harvester with modulator according to claim 1 or 2, characterized in that the second input terminal (RF2) simultaneously constitutes the ground of the entire RFID circuit (gnd).

4. The RFID harvester with modulator according to claim 1 or 2 or 3, characterized in that it operates substantially at a frequency of 13.56 MHz of the input signal.

5. The RFID harvester with modulator according to any of the claims from 1 to 4, characterized in that between the first input terminal (RF 1) and the first output terminal (HRV) a diode is connected, which was formed from the channel of a transistor (Td), which gate is connected to the first input terminal (RF1).

6. The RFID harvester with modulator according to any of the claims from 1 to 5, characterized in that it has a total of 3 or 4 stages.

7. The RFID harvester with modulator according to any of the claims from 1 to 6, characterized in that the resistor (R) is connected to the output of the last or one before the last stage of the harvester.

8. The RFID harvester with modulator according to any of the claims from 1 to 6, characterized in that the transistor (Tz) constituting the current source is connected to the output of the last or one before the last stage of the harvester.

9. The RFID harvester with modulator according to any of the claims from 1 to 8, characterized in that all transistors in the circuit are the FETs of "n" type.

10. The RFID harvester with modulator according to any of the claims from 1 to 9, characterized in that all transistors in the circuit are TFT-type transistors.

11. The RFID harvester with modulator according to any of the claims from 1 to 10, characterized in that the transistor channels are made of amorphous semiconductor material.

12. The RFID harvester with modulator according to any of the claims from 1 to 11, characterized in that the transistors contain indium-gallium zinc oxide.

13. The RFID harvester with modulator according to any of the claims from 1 to 12, characterized in that the channel lengths of the transistors used in the harvester stages range from 400 to 1000 nm.

14. The RFID harvester with modulator according to any of the claims from 1 to 13, characterized in that the width-to-length ratio of transistor channels used in the harvester stages ranges from 100 to 300.

15. The RFID harvester with modulator according to any of the claims from 1 to 14, characterized in that the width-to-length ratio of the modulation transistor channel (Tm) ranges from 20 to 50.

16. The RFID harvester with modulator according to any of the claims from 1 to 15, characterized in that the width-to-length ratio of the transistor channel (Tz) constituting the current source ranges from 0.1 to 0.5.

17. The RFID harvester with modulator according to any of the claims from 1 to 16, characterized in that the capacitances of the capacitors used in the harvester stages range from 30 to 80 pF.

18. The RFID harvester with modulator according to any of the claims from 1 to 17, characterized in that the ratio of the capacitance of capacitors used in the first harvester stage to the capacitance of capacitors used in the remaining harvester stages is 1 to 3.