EP2692451B1 - Electrical circuit for operating a transceiver unit - Google Patents

Description

State of the art

The present invention relates to an electrical circuit for operating a transceiver unit such as can be used, for example, in connection with ultrasonic transceivers. In particular, the present invention relates to an improved electrical circuit for shortening the settling time of a transceiver unit.

Transceiver units can be used according to the prior art for many different applications. For example, they are used for distance measurements in motor vehicles, with radar-lidar and sound transducers in particular being used as transceiver units in order to be able to deduce a current distance of the vehicle from the surrounding object from a signal that is transmitted and reflected by an environmental object. In the case of an ultrasonic transducer, a piezo diaphragm is used for this purpose, for example. During the transmission process, electrical energy is applied to generate sound, while after the transmission process and after residual membrane vibrations have decayed, sound arriving at the membrane is converted into electrical signals. As is known, it is necessary here for the transmission pulse to have as short a duration as possible in order to be able to recognize reflection sound impinging on the membrane from the decaying membrane vibrations a short time later. In order to still be able to emit high transmission energy, it is desirable to generate a maximum of membrane amplitudes right from the start of the transmission process and to maintain these over the entire (short) transmission process. In order to generate high amplitude oscillations using signal generators that are as weak as possible generate, in the prior art the signal generator is often excited with a first resonant circuit (for example, consisting of a series connection of a coil and a capacitor), and the voltage at one of the two energy stores is used as an input variable for a second resonant circuit comprising the transceiver unit. In this case, the second resonant circuit can consist exclusively of the transceiver unit (which can easily oscillate) or comprise further energy stores. However, a certain period of time is required to excite both resonant circuits in order to generate sufficient amplitudes at the transceiver unit for a transmission process. This period of time limits, among other things, the so-called close measurement capability of a distance measurement system.

The pamphlet DE 198 14 331 A1 describes a device for generating acoustic pressure pulses, in which two LC resonant circuits are coupled to one another and use a common capacitor.

The pamphlet FR 2 757 009 A1 relates to a device for operating a piezoelectric signal converter, in which an amplifier and a control circuit can be coupled to one another via a switch.

The pamphlet DE 195 48 161 C1 also describes a device for operating a piezo element, in which an excitation source can be coupled to the piezo element via a switch.

It is an object of the present invention to create an electrical circuit for the operation of a transceiver unit, by means of which the close-range measurement capability of an ultrasound-based distance measurement system can be improved in use.

Disclosure of the invention

The above-mentioned object is achieved according to the invention by an electrical circuit having the features according to claim 1. Advantageous further developments are the subject of the respective dependent claims.

Accordingly, an electrical circuit is proposed which is suitable for operating a transceiver unit, for example an ultrasonic transceiver. The circuit includes a first resonant circuit for generating a transmission signal and a second resonant circuit with a transceiver unit. The first resonant circuit can be coupled to a signal generator or a signal source whose or whose signal can excite the first resonant circuit to oscillate. The second resonant circuit can for example comprise one or more sound transducers, by means of which sound energy can be emitted on the one hand and sound energy can be absorbed and converted into electrical signals on the other hand. In this case, the second resonant circuit can consist exclusively of the transceiver unit (which can easily oscillate) or comprise further energy stores. The electrical circuit according to the invention further comprises a switching unit, the switching unit being set up to couple the first resonant circuit and the second resonant circuit to one another. In other words, the switching unit can ensure that electrical energy stored in the first resonant circuit can reach the second resonant circuit.

According to the invention, this is caused in response to a first predefined threshold value of a state variable of the first resonant circuit being reached. In other words, for example, a current and / or a voltage in one and / or both energy stores of the first resonant circuit can reach a predefined value and, in response to this, the switching unit can be caused to couple the first resonant circuit and the second resonant circuit to one another. In this way, a reflection can still be expected and evaluated in the second resonant circuit, while energy is already being collected in the first resonant circuit for a further transmission process without this being superimposed on the received signal.

The subclaims show preferred developments of the invention.

The threshold value of the state variable can preferably be a minimum amplitude of a variable coupled to the oscillation energy of the first resonant circuit. For example, a voltage and / or a current across a capacitance of the first resonant circuit can be used as a variable which causes a switching process of the switching unit. Alternatively or additionally, a current and / or a voltage can be used in an inductance of the first resonant circuit. This has the advantage that there is a simple possibility of determining a suitable trigger time for a switching process, which can be used as an input variable, for example, by a transistor as a switching unit by means of analog circuit technology.

More preferably, the switching unit can be set up to connect an output of the first resonant circuit to an input of the second resonant circuit. In other words, an electrical connection can be established between the first resonant circuit and the second resonant circuit for coupling the two resonant circuits through the switching unit. This offers the advantage that the transceiver unit remains voltage-free until it is coupled to the first resonant circuit.

The output of the first resonant circuit can preferably be arranged in parallel to an energy store of the first resonant circuit. In other words, the signal is tapped at a first connection of an energy store lying parallel to the output, the second connection of which with the electrical ground is connected. The switching unit, which in the closed state connects the output of the first resonant circuit to the input of the second resonant circuit, can now be connected to the first connection. The above-mentioned arrangement represents a simple embodiment that is easy to control in terms of circuitry.

Alternatively or additionally, the switching unit can be set up to electrically couple a connection on the ground side of the transceiver unit to the electrical ground. In other words, the switching unit or an additional switching unit can establish a connection between the transceiver unit and the electrical ground without the interposition of further electrical components. In contrast to the structure described above, according to which an electrical connection is switched between the two oscillating circuits, the alternative offers a simpler way of controlling the switch.

More preferably, the transceiver unit of the second resonant circuit can be designed as an ultrasonic transducer or at least include one. This offers the advantage that, on the one hand, this technology can be safely controlled and, on the other hand, the required ultrasonic transducers are manufactured in large numbers for automobile construction, so that a circuit according to the invention can be produced cost-effectively. Since, as will be discussed in connection with the attached drawing figures, an ultrasonic transducer based on piezo itself already behaves like an electrical oscillating circuit, no further electrical components apart from such an ultrasonic transducer need to be provided for the construction of the second oscillating circuit. This offers the advantage of a particularly simple and inexpensive construction of an electrical circuit according to the invention.

More preferably, a transistor, in particular a field effect transistor, extremely preferably a metal oxide layer field effect transistor (MOSFET) can be provided as the switching unit. This offers the advantage that, on the one hand, transistors can be manufactured as mass-produced articles and can therefore be purchased cheaply, and on the other hand, in particular in connection with the aforementioned field-effect transistors, low switching and blocking losses occur.

More preferably, a signal source can be coupled to the first resonant circuit, wherein the coupling can in particular be permanent, in other words not switchable. This offers the advantage of a particularly simple structure, while the functional reliability is increased.

The subclaims show preferred developments of the invention.

Brief description of the drawings

Figur 1

ein Schaltbild eines typischen Ausführungsbeispiels gemäß dem Stand der Technik,

Figur 2

ein Schaltbild eines Ausführungsbeispiels gemäß der vorliegenden Erfindung,

Figur 3

zwei Diagramme, veranschaulichend die Spannung zur Anregung des ersten Schwingkreises (oben) und die resultierende Spannung an der Sendeempfangseinheit (unten),

Figur 4

ein Zeitdiagramm von Strömen durch eine Sendeempfangseinheit gemäß dem Stand der Technik und der vorliegenden Erfindung (oben) und ein Zeitdiagramm von Spannungen an der Sendeempfangseinheit gemäß dem Stand der Technik und der vorliegenden Erfindung (unten), und

Figur 5

zwei Zeitdiagramme zur Veranschaulichung der unterschiedlichen Anregungsdauer nach dem Stand der Technik und nach der vorliegenden Erfindung.

Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawings is:

Figure 1

a circuit diagram of a typical embodiment according to the prior art,

Figure 2

a circuit diagram of an embodiment according to the present invention,

Figure 3

two diagrams illustrating the voltage to excite the first resonant circuit (above) and the resulting voltage at the transceiver unit (below),

Figure 4

a timing diagram of currents through a transceiver unit according to the prior art and the present invention (above) and a timing diagram of voltages at the transceiver unit according to the prior art and the present invention (below), and

Figure 5

two timing diagrams to illustrate the different excitation duration according to the prior art and according to the present invention.

Embodiments of the invention

Figure 1 shows an electrical circuit such as is used in the prior art for the use of an ultrasonic transceiver. A Signal source 4 is set up to apply a sinusoidal voltage to an oscillating circuit consisting _{of a coil L 1} of, for example, 285 μH and a capacitor C _{1 of 46 nF.} In parallel with the capacitor C ₁ , the equivalent circuit diagram of a transceiver 2 is shown, which consists of a parallel connection of four branches. The first branch consists of a capacitance C ₂ of 2 nF. The second branch consists of an inductance L ₃ of 350 mH, a _{capacitance C 3} of 40 pF connected in series with _{the inductance L 3} and an ohmic load R ₃ of 3 kΩ also connected in series. The third branch consists of an inductance L ₄ of 50 μH, a capacitor C ₄ of 40 pF and an ohmic load R ₄ of 3 kΩ. Finally, the fourth branch consists of a coil L ₅ of 20 mH, a capacitance C ₅ of 40 pF and an ohmic load R ₅ of 3 kΩ. A switching unit is not provided, so that the signal source 4 always sees both resonant circuits or the entire illustrated arrangement of passive elements as a load.

Figure 2 shows a circuit diagram of an embodiment according to the present invention. A signal source 4 drives an oscillating circuit SK ₁ , which consists of a series connection of a first inductance L ₁ and a first capacitance C ₁ . An output terminal 3 of the first resonant circuit SK _{1 is} arranged between the inductance L ₁ and the capacitance C _1. A first switch S ₁ for coupling the two oscillating circuits SK ₁ and SK _{2 is connected} to the output terminal 3. With the switch S ₁ is already in connection with Figure 1 discussed equivalent circuit diagram of an ultrasonic transducer 2 connected as a transceiver unit. _{On the ground side, a second switch S 2} (dashed lines) is provided as a second switching unit S ₂ between the ultrasonic transducer 2 and the electrical ground 10. The elements of the equivalent circuit diagram of the transceiver unit 2 agree with those in Figure 1 match shown, so that a detailed discussion of these can be dispensed with for the sake of brevity. The function of the circuit according to the invention is as follows: The signal source excites the first resonant circuit SK ₁ , in response to which voltage amplitudes that are many times higher than the signal source 4 alone can be set across the capacitance C _1. In response to reaching a first threshold value, which corresponds to amplitudes suitable for a transmit / receive process, the first switch S _{1 is} closed, whereby the voltages applied across the first capacitance C _{1 are} now generated by the ultrasonic transducer _Two -pole as the second SK 2 resonant circuit are present. The above statements apply in the event that the second switch S _{2 is} either closed or not present. The second switch S ₂ could be used identically while the first switch S _{1 is} closed or not present. The mode of operation results for the second switch S ₂ accordingly. After the transmission process has ended, the switch used in each case (or, if both switches S ₁ / S ₂ are used, at least one of the two switches S ₁ / S ₂ ) is opened so that no more energy from the first resonant circuit SK ₁ into the second resonant circuit SK ₂ arrives and the membrane of the transceiver unit 2 decays or is, for example, passively or actively attenuated in a known manner. Echoes arriving at the transceiver unit 2 can in turn cause the membrane of the transceiver unit 2 to vibrate and can be detected in a known manner from the electrical signal of the transceiver unit 2.

Figure 3 shows in its upper half a timing diagram of a voltage signal V ₄ , as indicated by the in Figure 2 signal source 4 shown could be generated. The alternating voltage shown has an amplitude of 3 V. Due to the first resonant circuit SK ₁ , a significantly higher amplitude results after some time, for example for the voltage across the first capacitance C ₁ . This voltage is already used in the prior art to apply an electrical signal suitable for transmission to the transceiver unit 2. In the lower half of Figure 3 a voltage V _{2 is} plotted against time, which occurs in a circuit according to the prior art (see FIG Figure 1 ) could result on the ultrasonic transducer without a switching process according to the invention. It can be seen that from the point in time from which the signal source 4 _{outputs a voltage V 4} , a voltage V ₂ is also applied across the ultrasonic transducer, which, however, only reaches its maximum amplitude at the same time as the end of the voltage signal V ₄ . The amplitude of the voltage V ₂ then decays essentially with an exponential function.

Figure 4 shows in its upper half a comparison of time diagrams of two currents as they _{would flow according to the present invention I 2E} ) or according to the prior art I _2PA ) with a corresponding excitation through the ultrasonic transducer 2. The lower half of Figure 2 shows the corresponding voltage _{signals (V 2E} : voltage at the ultrasonic transducer 2 according to FIG present invention, V _2PA : voltage at the ultrasonic transducer 2 according to the prior art), which corresponds to the respective currents, as shown in the upper half of FIG Figure 4 are shown belong. The voltage profile according to the prior art V _2PA essentially corresponds to that in the lower half of FIG Figure 3 shown course. Since the first resonant circuit is not fully excited at the beginning of the excitation of the ultrasonic transducer 2, the amplitude of the voltage V _{2PA increases} only slowly. The same applies in particular to the current I _2PA through the ultrasonic transducer 2 in the upper half of the Figure 4 . Thus, energy is only "pumped" slowly into the second resonant circuit SK _2. Significantly different courses result according to the present invention. The voltage V _2E in the lower half of Figure 4 begins with a maximum amplitude, since at the time of switching the first resonant circuit SK _{1 is} already fully excited and thus the voltage across the first capacitance C _{1 has} already reached its maximum. The excitation of the ultrasonic transducer 2 with maximum voltages leads to a significantly faster increase in the current I _2E flowing through it. In other words, the signal amplitudes required for a transmission process result much earlier, so that the required sound energy can be emitted by the ultrasonic transducer 2 within a shorter time. Since the transmission process ends earlier in this way and the membrane vibrations have decayed to the extent required for a reception process, echoes from the signal of the ultrasonic transducer 2 can be detected at an earlier point in time than in the prior art. In this way, the so-called “near detection threshold” can be significantly reduced, so that surrounding objects arranged close to the vehicle or to the ultrasonic transducer 2 can also be reliably detected.

Figure 5 shows two voltage _{curves (V 4E} , V 4PA) for the excitation of the first resonant circuit SK ₁ by the signal source 4, the upper voltage V _{4E being switched on} earlier and switched off earlier than the voltage V 4PA shown below. Although the first resonant circuit _{is supplied with energy at an earlier point in time with the voltage V 4E} , this does not interfere with ongoing receiving processes in the second resonant circuit, since according to the present invention there is no coupling of the resonant circuits at this point in time. The later signal start of the voltage V _4PA according to the prior art coincides in time with the time of excitation of the second resonant circuit. In order to have enough energy for the transmission process To be able to emit the transceiver, according to the prior art, however, a longer excitation time of the second oscillating circuit SK _{2 is} required than according to the present invention. Therefore, shorter pulses can be realized by the present invention, which allow a better range resolution and a better resolution of multiple echoes.

It is a core concept of the present invention to initially supply a first resonant circuit used to generate a transmission signal for a transceiver device with energy without the transceiver device being able to absorb portions of this energy. Only when the energy that can be given off within the first resonant circuit has reached a predetermined level is a switching device enabled to transfer energy from the first resonant circuit to the transceiver unit, which is preferably arranged in a second resonant circuit. Different solutions have been proposed for the arrangements and configurations of the switching unit. The subject matter of the present invention makes it possible, for example, to bring electrical energy into the first resonant circuit by means of the transceiver unit while a receiving process is still in progress and thus to prepare a transmission process following the receiving process.

Even if the aspects according to the invention and advantageous embodiments have been described in detail with reference to the embodiments explained in connection with the accompanying drawing figures, modifications and combinations of features of the embodiments shown, in particular with further solutions known from the prior art and Features, possible without departing from the scope of the present invention, the scope of which is defined by the appended claims.

Claims (9)

1. Electrical circuit (1) for the operation of a transceiver unit (2), wherein the circuit (1) comprises:

   - a first resonant circuit (SK₁) for generating a transmission signal,

   - a second resonant circuit (SK₂) comprising a transceiver unit (2) and

   - a switching unit (S₁, S₂),
   characterized
   in that the switching unit (S₁, S₂) is designed to couple the first resonant circuit (SK₁) and the second resonant circuit (SK₂) to one another when a state variable of the first resonant circuit (SK₁) has exceeded a predefined threshold value.
2. Electrical circuit (1) according to Claim 1, wherein the state variable is a minimum amplitude of a variable linked to the vibrational energy of the first resonant circuit (SK₁).
3. Electrical circuit (1) according to Claim 1 or 2, wherein the switching unit is designed to connect an output (3) of the first resonant circuit (SK₁) to an input of the second resonant circuit (SK₂).
4. Electrical circuit (1) according to Claim 3, wherein the output (3) together with a connection, connected to the electrical earth (10), of the first resonant circuit (SK₁) is arranged in parallel with an energy store (C1) of the first resonant circuit (SK₁).
5. Electrical circuit (1) according to Claim 4, wherein the energy store is a capacitor (C1) or a coil (L1).
6. Electrical circuit (1) according to one of the preceding claims, wherein the switching unit (S₁, S₂) is designed to electrically couple an earth-side connection (5) of the transceiver unit (2) to the electrical earth (10) .
7. Electrical circuit (1) according to one of the preceding claims, wherein the transceiver unit (2) comprises an ultrasound transducer.
8. Electrical circuit (1) according to one of the preceding claims, wherein the switching unit (S₁, S₂) is a transistor and/or a metal oxide layer field-effect transistor.
9. Electrical circuit (1) according to one of the preceding claims, wherein a signal source (4) is also coupled or permanently coupled to the first resonant circuit (SK₁) .

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