DE102014220260A1 - Antenna multiplexer, driver circuit with a switching element and active transmitting device with a switching element - Google Patents

Abstract

Switching element (71) having a first and a second transistor (711, 712), wherein a first load terminal (S) of the first transistor (711) is connected to a first load terminal (S) of the second transistor (712) and the first transistor (7) 711) receives a first voltage (U1) at a second load terminal (D). The switching element includes a potential generation unit (713) configured to provide a potential at an output terminal in an activated state, and a control unit (714) configured to receive the potential generated by the potential generation unit (713). to provide a control voltage (Ugs) to the first transistor (711) and the second transistor (714), and to vary the control voltage (Ugs) in response to a temperature in the switching element (71). The control voltage (Ugs) is always greater than a voltage which is the sum of the first voltage (U1) and a threshold voltage (Uth) of the first transistor (711) minus a voltage (Ug) at the control terminal (G) of the first transistor ( 711).

Description

The invention relates to a multiplexer with a switching element, in particular with a switching element with field effect transistors, a driver circuit with a switching element and an active transmitting device with a switching element, in particular in a keyless vehicle access and start system.

Keyless vehicle entry and start systems, such as the Passive Start Entry (PASE) system, are automatic systems for unlocking a vehicle without actively using a car key and starting it just by pressing the start button. This is made possible by an electronic key with a chip, which the vehicle driver carries with him. Periodically, from a base station in the vehicle via at least one antenna located on the vehicle, a request signal coded by means of a first coding table is transmitted on an LF frequency (LF stands for "low frequency" with frequencies between, for example, 20 kHz and 200 kHz). The base station then switches to a receive mode in the UHF range (UHF stands for "Ultra High Frequency" with frequencies in the three-digit MHz range, for example) and waits for confirmation. If a transponder-equipped key is in range, it receives the LF signal, decodes it, and retransmits it using a second encoding table with a new encoding as the UHF signal. The UHF signal is decoded by the base station. Since the base station knows both coding tables, it can compare its own original transmission with the signal just received and grant access if it matches. If there is no correct answer within a defined time, nothing happens and the base station returns to standby. The engine start process essentially corresponds to that of the access control, except that here the engine start button is actuated.

As an antenna for transmitting the LF signal is predominantly an inductive antenna use, which is designed for example as a winding provided with a ferrite core (also known as magnetic or ferrite antenna). The inductance of the inductive antenna is often operated together with a capacitor in a resonant circuit. A base station can also have more than one antenna (and thus also several oscillating circuits), for example to cover several areas around the vehicle. The different antennas can, as in the publication DE 198 35 155 A1 described, are individually controlled by means of separate drivers. However, since such a solution requires a considerable amount of circuitry, base stations are known with only one driver for multiple antennas, the individual antennas can be controlled via a multiplexer. From the publication DE 10 2004 011 927 A1 For example, a transmitting device is known in which a multiplexer is arranged on the side of the antenna facing away from the driver. However, it is also possible to arrange a multiplexer between the driver and the antennas, as in the EP 0 741 221 B1 described.

The multiplexer used may be embodied in a MOSFET technology, that is to say that the multiplexer has MOSFETs which can be turned on via a control signal at its gate terminal and activate or deactivate a respectively assigned antenna in accordance with the control signal.

One problem, however, is that the resistance of the transistors used changes with a change in temperature. This has a negative effect on the quality of the respective antenna resonant circuit and on the strength of the radiated from the respective antenna electromagnetic field.

The object of the invention is to provide an improved switching element of an antenna multiplexer in this respect. Furthermore, an improved driver circuit with a switching element and an improved active transmitting device with a switching element are to be provided.

The object is achieved by an antenna multiplexer according to claim 1, a driver circuit according to claim 10, or an active transmitting device according to claim 11.

The inventive antenna multiplexer (hereinafter multiplexer) has a switching element with a first transistor and a second transistor, each having a first load terminal, a second load terminal and a control terminal, wherein the first load terminal of the first transistor with the first load terminal of second transistor is connected and the first transistor receives at its second load terminal, a first voltage. The switching element further comprises a potential generation unit configured to provide a potential at an output terminal in an activated state, and a control unit configured to receive the potential generated by the potential generation unit, a control voltage at the first transistor and at the second Transistor to provide and change the control voltage in dependence on a temperature in the switching element, wherein the control voltage is always greater than a voltage which is the sum of the first voltage and a Threshold voltage of the first transistor, minus a voltage at the control terminal of the first transistor corresponds.

In this way, a change in the resistance between the first load terminals and the second load terminals of the transistors over the temperature can be significantly reduced. Thus, the quality of an antenna resonant circuit connected to the switching element and thus also the strength of an electromagnetic field emitted by the antenna remains substantially constant.

The control unit may be configured to increase the control voltage as the temperature in the switching element increases and decreases as the temperature in the switching element decreases.

The control unit can have at least one diode which has a greater diffusion voltage at lower temperatures than at higher temperatures. Thus, the control unit can be implemented in a simple manner without much circuit complexity.

The first transistor and the second transistor may be formed as MOSFETs, in particular as n-channel MOSFETs, wherein in each case the first load terminal is a source terminal, the second load terminal is a drain terminal and the control terminal is a gate terminal and the control voltage is a gate terminal. Tension is.

The temperature in the switching element may be a temperature in the first or second transistor or in both transistors.

The potential generation unit may include a charge pump or a bootstrap circuit to provide a sufficiently high control voltage.

The potential generation unit may be configured to receive a control signal and provide a potential when the control signal is present or has a predetermined level. A control voltage which enables the transistors to be turned on and thereby the activation of a subsequent antenna is thus provided only if this is actually desired.

The first voltage may be a trapezoidal, a rectangular or a sinusoidal voltage.

An inductance driver circuit has a driver stage configured to provide a first voltage. The driver circuit furthermore has a multiplexer (in particular an antenna multiplexer as described above) with at least two switching elements, the switching elements each having a first transistor and a second transistor, each having a first load terminal, a second load terminal and a control terminal the first load terminal of the first transistor is connected to the first load terminal of the second transistor, and the first transistor receives the first voltage on its second load terminal. The switching elements further each have a potential generating unit, which is designed to provide a potential at an output terminal in an activated state, and a control unit, which is configured to receive the potential generated by the potential generating unit, a control voltage at the first transistor and at second transistor, and to vary the control voltage in response to a temperature in the switching element, wherein the control voltage is always greater than a voltage corresponding to the sum of the first voltage and a threshold voltage of the first transistor, minus a voltage at the control terminal of the first transistor ,

An active transmitting device has at least two inductive antennas, a driver stage, which is designed to provide a first voltage, and a multiplexer with at least two switching elements, wherein the switching elements each have a first transistor and a second transistor, each having a first load terminal, a second load terminal and a control terminal, wherein the first load terminal of the first transistor is connected to the first load terminal of the second transistor and the first transistor receives the first voltage at its second load terminal. The switching elements further each have a potential generating unit, which is designed to provide a potential at an output terminal in an activated state, and a control unit, which is configured to receive the potential generated by the potential generating unit, a control voltage at the first transistor and at second transistor and to change the control voltage in dependence on a temperature in the switching element, wherein the control voltage is always greater than a voltage corresponding to the sum of the first voltage and a threshold voltage of the first transistor, minus a voltage at the control terminal of the first transistor.

The invention will be explained in more detail with reference to the embodiments illustrated in the figures of the drawing. It shows:

1 in a circuit diagram, a driver circuit for an inductance in an application as an active transmitting device for LF signals,

2 in a circuit diagram, a switching element with a first circuit for temperature compensation,

3 in a circuit diagram, a switching element with another circuit for temperature compensation.

1 shows a driver circuit for a plurality of inductors, which in the present case by inductive antennas 11 . 12 . 13 , which may be ferrite antennas (wound ferrite cores), for example, when used as an active transmitting device. The driver circuit and the inductive antennas may be part of a keyless vehicle access and start system. The inductive antennas 11 . 12 . 13 can substitute as in the 1 represented by an electrical series circuit of a purely inductive component 21 . 22 . 23 and an ohmic share 31 . 32 . 33 to be discribed. A capacity 41 . 42 . 43 is in each case between the inductive antenna 11 . 12 . 13 and a connection for a reference potential M is connected.

An ohmic resistance 51 . 52 . 53 is in each case between the inductive antennas 11 . 12 . 13 and a multiplexer 60 connected. Through the resistance 51 . 52 . 53 , the inductive antennas 11 . 12 . 13 as well as the capacity 41 . 42 . 43 a branch is formed in each case a resonant circuit. The multiplexer 60 has a number of switching elements 71 . 72 . 73 on, where the number of switching elements 71 . 72 . 73 the number of inductive antennas 11 . 12 . 13 equivalent. Each of the switching elements 71 . 72 . 73 is an inductive antenna 11 . 12 . 13 assigned and is adapted to the respective antenna 11 . 12 . 13 to activate (switching element 71 . 72 . 73 closed) or to deactivate (switching element 71 . 72 . 73 open). For this, each of the switching elements receives 71 . 72 . 73 a control signal S21, S22, S23. A switching element 71 . 72 . 73 For example, it can be closed if the corresponding control signal S21, S22, S23 is present or has a certain level. An operating voltage Ur of the multiplexer 60 can be provided by a vehicle battery (eg directly, or indirectly via a voltage regulator).

The operating voltage Ur can continue (directly, or indirectly via a voltage regulator) a driver stage 80 to be provided. The driver stage 80 may comprise an amplifier to which a control signal S10 is provided at an input. The effective amplification factor of the driver stage 80 depends on the height of the operating voltage Ur. The input side with the control signal S10 driven driver stage 80 generated during operation of the driver circuit on the output side, a voltage U1, which for driving the antennas 11 . 12 . 13 is used when the corresponding switching element 71 . 72 . 73 closed is. The voltage U1 may be, for example, trapezoidal, sinusoidal or rectangular.

A switching element 71 . 72 . 73 (the multiplexer 60 ) may comprise two transistors, which may be formed as MOSFETs. This is in 2 by way of example with reference to a switching element 71 shown. The switching element 71 has a first MOSFET 711 and a second MOSFET 712 on. In the 2 shown MOSFETs are n-channel MOSFETs. MOSFET stands for Metal-Oxide-Semiconductor Field-Effect Transistor (German: Metal-Oxide-Semiconductor Field Effect Transistor). A MOSFET is a three-terminal active device. These are a control terminal (gate terminal) G, a first load terminal (source terminal) S and a second load terminal (drain terminal) D. A MOSFET acts like a voltage-controlled resistor, that is, via a control voltage (gate voltage ) Ugs a resistor between drain terminal D and source terminal S, and thus a current through the transistor can be changed. This resistance is temperature dependent. In the case of small resistors, only a slight increase in resistance results in an increase in the temperature. For large resistors, however, a temperature increase has a noticeable effect on the resistance. In a temperature range of -40 ° to + 105 ° C, the resistance can vary by a factor of 3. This has a negative effect on the quality of the subsequent resonant circuit.

The two MOSFETs 711 . 712 are connected to each other with their source terminals S. Its drain D is the first MOSFET 711 with the driver stage 80 (in 2 not shown). The second MOSFET 712 is with its drain terminal D with the resonant circuit (in 2 not shown). This arrangement ensures that in a locked state of MOSFETs 711 . 712 there is no conductive connection between the two drain terminals D. The MOSFETs 711 . 712 each have a parasitic diode between their drain and source terminals D, S. These diodes are switched antiseries in the present arrangement and thus prevent a conductive connection in the deactivated state.

To the switching element 71 to turn on to activate the resonant circuit, a gate voltage Ugs is required, which is around a threshold voltage Uth of the first MOSFETs 711 is greater than the driver stage 80 generated voltage U1 minus a voltage Ug of the first MOSFETs 711 (Ugs> (U1 + Uth - Ug), where the voltage Ug is a voltage at the gate terminal G of the first MOSFET 711 is based on a ground potential. The threshold voltage Uth of a MOSFET (often referred to as the threshold voltage) is generally between 1V and 3V, but may be greater or none. In this case, the gate voltage Ugs is less than a voltage equal to the sum of the voltage through the driver stage 80 generated voltage U1 and the threshold voltage Uth of the first MOSFETs 711 , minus the voltage Ug of the first MOSFET (that is, if Ugs <(U1 + Uth - Ug)), the MOSFETs 711 . 712 do not lead. To generate a sufficiently high gate voltage Ugs are a potential generation unit 713 and a control unit 714 intended. The potential generation unit 713 the operating voltage Ur is also provided. At an input receives the potential generation unit 713 the control signal S21. When the control signal S21 is applied or when it has a predetermined level, the potential generation unit stops 713 a potential ready at its exit.

The potential generation unit 713 may have a charge pump or a bootstrap circuit. In order to generate a gate voltages Ugs, the current temperature of the MOSFETs 711 . 712 adjusted, receives the control unit 714 at an input from the potential generation unit 713 provided potential. The control unit 714 is further connected to the terminal for the reference potential M. With a first exit is the control unit 714 with the gate terminals G of the MOSFETs 711 . 712 connected. With a second output is the control unit 714 connected to a common circuit node of the source terminals S. The control unit 714 Thus, at its outputs, a gate voltage Ugs for the MOSFETs 711 . 712 provide.

The control unit 714 is adapted to the gate voltage Ugs to a temperature in the switching element 71 adapt. Thus, the gate voltage Ugs can be smaller at lower temperatures than at higher temperatures. At lower temperatures, the resistance between drain D and source S can thus be increased, while the MOSFETs have their optimally achievable resistance at higher temperatures. The temperature in the switching element 71 can the temperature in the transistors 711 . 712 be.

The control unit 714 For example, to change the gate voltage Ugs, at least one diode may be used 715 have, as in 3 shown. The at least one diode 715 has a larger diffusion voltage at lower temperatures than at high temperatures, so that the gate voltage Ugs provided varies with temperature. The diffusion voltage is a potential difference across a space charge zone, which counteracts the diffusion of charge carriers. A semiconductor diode has a pn junction. At the boundary between the n-doped and the p-doped semiconductor, the diffusion gradient leads to the diffusion of charge carriers. That is, free electrons from the n-region migrate to the p-region. Similarly, holes (holes) migrate from the p-region to the n-region. Among other things, it comes to the recombination of electrons and holes. As a result of this charge carrier movement (diffusion current), an electric counter field forms between these space charges in the interior of the semiconductor crystal, which counteracts the further diffusion of mobile charge carriers, since it generates an opposite drift current. The electrical voltage generated by the electric opposite field is referred to as the diffusion voltage.

The use of at least one diode 715 is only an example. It is also possible, the gate voltage Ugs in another way to a temperature in the switching element 71 adapt.

Overall, by the in the 2 and 3 shown switching element, the change in the resistance between the drain D and source S over the temperature can be significantly reduced.

LIST OF REFERENCE NUMBERS

11

 inductive antenna

12

 inductive antenna

13

 inductive antenna

21

 inductive component

22

 inductive component

23

 inductive component

31

 resistive component

32

 resistive component

33

 resistive component

41

 capacity

42

 capacity

43

 capacity

51

 ohmic resistance

52

 ohmic resistance

53

 ohmic resistance

60

 multiplexer

71

 switching element

72

 switching element

73

 switching element

80

 driver stage

711

 first transistor

712

 second transistor

713

 Potential generating unit

714

 control unit

715

 diode

G

 Gate terminal

D

 Drain

S

 Source terminal

ur

 operating voltage

U1

 first tension

coll

 Gate voltage

S10

 control signal

S21

 control signal

S22

 control signal

S23

 control signal

M

 reference potential

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19835155 A1 [0003]
• DE 102004011927 A1 [0003]
• EP 0741221 B1 [0003]

Claims (11)

Antenna Multiplexer ( 60 ) with at least one switching element ( 71 ), wherein the switching element ( 71 ) comprises: a first transistor ( 711 ) and a second transistor ( 712 ), each having a first load terminal (S), a second load terminal (D) and a control terminal (G), wherein the first load terminal (S) of the first transistor ( 711 ) with the first load terminal (S) of the second transistor ( 712 ) and the first transistor ( 711 ) receives at its second load terminal (D) a first voltage (U1); a potential generation unit ( 713 ) configured to provide a potential at an output terminal in an activated state; and a control unit ( 714 ), which is adapted to that of the potential generation unit ( 713 ), a control voltage (Ugs) at the first transistor ( 711 ) and at the second transistor ( 714 ), and the control voltage (Ugs) in dependence on a temperature in the switching element (FIG. 71 ), wherein the control voltage (Ugs) is always greater than a voltage which is the sum of the first voltage (U1) and a threshold voltage (Uth) of the first transistor ( 711 ), minus a voltage (Ug) at the control terminal (G) of the first transistor ( 711 ) corresponds. Antenna Multiplexer ( 60 ) according to claim 1, wherein the control unit ( 714 ) is adapted to increase the control voltage (Ugs) when the temperature in the switching element ( 71 ) increases and decreases when the temperature in the switching element ( 71 ) decreased. Antenna Multiplexer ( 60 ) according to claim 2, wherein the control unit ( 714 ) at least one diode ( 715 ) which has a larger diffusion voltage at lower temperatures than at higher temperatures. Antenna Multiplexer ( 60 ) according to one of claims 1 to 3, wherein the first transistor ( 711 ) and the second transistor ( 712 ) are formed as a MOSFET, wherein in each case the first load terminal (S) is a source terminal, the second load terminal (D) is a drain terminal, the control terminal (G) is a gate terminal and the control voltage (Ugs) is a gate voltage , Antenna Multiplexer ( 60 ) according to claim 4, wherein the MOSFETs are formed as n-channel MOSFETs. Antenna Multiplexer ( 60 ) according to one of the preceding claims, wherein the temperature in the switching element ( 71 ) a temperature in the first or second transistor ( 711 . 712 ) or in both. Antenna Multiplexer ( 60 ) according to one of the preceding claims, wherein the potential generation unit ( 713 ) has a charge pump or a bootstrap circuit. Antenna Multiplexer ( 60 ) according to one of the preceding claims, wherein the potential generation unit ( 713 ) is adapted to receive a control signal (S1) and to provide a potential when the control signal (S1) is applied or has a predetermined level. Antenna Multiplexer ( 60 ) according to one of the preceding claims, wherein the first voltage (U1) is a trapezoidal, a sinusoidal or a rectangular voltage. Driver circuit for an inductance ( 1 ) with a driver stage ( 80 ) configured to provide a first voltage (U1); and a multiplexer ( 60 ) with at least two switching elements ( 71 ) each having a first transistor ( 711 ) and a second transistor ( 712 ), each having a first load terminal (S), a second load terminal (D) and a control terminal (G), wherein the first load terminal (S) of the first transistor ( 711 ) with the first load terminal (S) of the second transistor ( 712 ) and the first transistor ( 711 ) receives at its second load terminal (D) the first voltage (U1); a potential generation unit ( 713 ) configured to provide a potential at an output terminal in an activated state; and a control unit ( 714 ), which is adapted to that of the potential generation unit ( 713 ), a control voltage (Ugs) at the first transistor ( 711 ) and at the second transistor ( 714 ), and the control voltage (Ugs) in dependence on a temperature in the switching element (FIG. 71 ), wherein the control voltage (Ugs) is always greater than a voltage which is a sum of the first voltage (U1) and a threshold voltage (Uth) of the first transistor (Ugs) 711 ), minus a voltage (Ug) at the control terminal (G) of the first transistor ( 711 ) corresponds. Active transmitting device with at least two inductive antennas ( 11 . 12 . 13 ), a driver stage ( 80 ) configured to provide a first voltage (U1); and a multiplexer ( 60 ) with at least two switching elements ( 71 ) each having a first transistor ( 711 ) and a second transistor ( 712 ), each having a first load terminal (S), a second load terminal (D) and a control terminal (G), wherein the first load terminal (S) of the first transistor ( 711 ) with the first load terminal (S) of the second transistor ( 712 ) and the first transistor ( 711 ) receives at its second load terminal (D) the first voltage (U1); a potential generation unit ( 713 ) configured to provide a potential at an output terminal in an activated state; and a control unit ( 714 ), which is adapted to that of the potential generation unit ( 713 ), a control voltage (Ugs) at the first transistor ( 711 ) and at the second transistor ( 714 ), and the control voltage (Ugs) in dependence on a temperature in the switching element (FIG. 71 ), wherein the control voltage (Ugs) is always greater than a voltage which is the sum of the first voltage (U1) and a threshold voltage (Uth) of the first transistor ( 711 ), minus a voltage (Ug) at the control terminal (G) of the first transistor ( 711 ) corresponds.

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