阅读说明：本技术 用于转换差分输入信号的开关装置和具有开关装置的系统 (Switching device for converting differential input signals and system having a switching device ) 是由 B·诺伦贝格 C·森夫特 S·里克特 H·J·科拉尔 M·马德尔 于 2020-02-27 设计创作，主要内容包括：本发明涉及一种用于以控制信号(S-EXT)将差分输入信号(S-DIFF-IN)转换为对地输出信号(S-OUT)的开关装置(1),其中,识别错误状态,所识别的错误状态导致对地输出信号(S-OUT)的关断,并且附加地显示在控制信号(S-EXT)上。(The invention relates to a switching device (1) for converting a differential input signal (S _ DIFF _ IN) into a ground output signal (S _ OUT) with a control signal (S _ EXT), wherein an error state is detected, which error state leads to a switch-off of the ground output signal (S _ OUT) and is additionally displayed on the control signal (S _ EXT).)

1. A switching device (1) for converting a differential input signal (S _ DIFF _ IN) with a control signal (S _ EXT) into a ground output signal (S _ OUT),

it is characterized in that the preparation method is characterized in that,

an error state, in particular an error state caused by an error in the level transition and/or the signal transmission time, is detected,

the identified error state results in a switch-off of the ground output signal (S _ OUT) and is additionally displayed on the control signal (S _ EXT), in particular in order to generate a defined signal state on the ground output signal (S _ OUT) while the number of interface signals remains unchanged and to achieve a time-optimized error correction.

2. The switching device (1) as claimed IN claim 1, wherein the switching device (1) comprises a differential stage (2) and an output stage (3), the differential stage (2) generating a first ground pair signal (S1) from the differential input signal (S _ DIFF _ IN) with a delay of a first signal transmission time t1, the output stage (3) generating a ground pair output signal (S _ OUT) from the first ground pair signal (S1), IN particular from a control signal (S _ EXT),

the switching device (1) comprises a further differential stage (4), an evaluation stage (5) and a bidirectional communication stage (6),

the further differential stage (4) generates a second ground signal (S2) from the differential input signal (S _ DIFF _ IN) with a delay of a second signal transmission time t2, IN particular wherein the second signal transmission time t2 is much shorter than the first signal transmission time t1,

the evaluation stage (5) generates a third ground signal (S3) on the basis of the first ground signal (S1) and the second ground signal (S2) taking into account the first signal transmission time t1 and the second signal transmission time t2,

the two-way communication stage (6)

-or from said third signal (S3)

-or from said third signal (S3) and at least one counterparty station

A control signal (S EXT) is generated,

the output stage (3) additionally passes a first ground-to-ground signal (S1) to a ground-to-ground output signal (S _ OUT) in accordance with the third ground-to-ground signal (S3).

3. The switching device (1) as claimed in claim 2, wherein the differential stage (2) achieves a ground reference by means of an opto-coupler (21), the output signal of the opto-coupler (21) being conducted via a filter element (22), a first switching element (23) delivering a supply Voltage (VCC) to the first ground signal (S1) depending on the output signal of the filter element (22), a first signal transmission time t1 of the differential stage (2) consisting of the sum of the switching time of the opto-coupler (21) and the switching time of the first switching element (23) and the delay time of the filter element (22).

4. The switching device (1) as claimed in one of the preceding claims, wherein the further differential stage (4) implements a second ground signal (S2) by means of a further opto-coupler (41), the second signal transmission time t2 of the further differential stage (4) substantially corresponding to the switching time of the further opto-coupler (41).

5. The switching device (1) according to one of the preceding claims, wherein the evaluation stage (5) evaluates the first ground signal (S1) and the second ground signal (S2) via at least one first logic gate (51), in particular via an XOR logic gate, an output signal of the first logic gate (51) being conducted via a further filter element (52),

the further filter element (52) has a delay time tf,

the delay time tf is selected as a function of the first signal transmission time t1, the second signal transmission time t2 and the signal transmission time tolerance value td, in particular wherein the delay time tf is | t2-t1| + td.

6. The switching device (1) according to one of the preceding claims, wherein the further filter element (52) comprises an RC filter (521) and a second logic gate (522), in particular an inverting logic gate, the nominal value of the RC filter being selected to tf R C, the second logic gate (522) digitizing the output signal of the RC filter (521) and generating the output signal of the further filter element (52), in particular wherein the second logic gate (522) is implemented in CMOS technology.

7. The switching device (1) according to any one of the preceding claims, wherein the output signal of the further filter element (52) corresponds to a third ground signal (S3).

8. The switching device (1) according to one of the preceding claims, wherein the output signal of the further filter element (52) sets a memory element (53), in particular an RS flip-flop, the output signal of a third logic gate (54), in particular a wide-OR logic gate, resets the memory element (53), the third logic gate (54) evaluates a first ground signal (S1) and a second ground signal (S2), the output signal of the memory element (53) corresponding to the third ground signal (S3).

9. The switching device (1) according to any one of the preceding claims, wherein the bidirectional communication stage (6) comprises a communication interface (61), in particular an open-drain interface, having a pull-up resistor (62) connected either to a supply Voltage (VCC) or to another supply voltage (VCC EXT), the control signal (S EXT) being short-circuited to ground potential (GND) via a second switching element (63) in dependence on the third ground-to-ground signal (S3), in particular in anti-phase.

10. The switching device (1) according to any one of the preceding claims, wherein the output stage (3) comprises a fourth switching element (31) and at least one fourth logic gate (32), the fourth switching element (31) passing the first ground pair signal (S1) to at least one supply voltage input of the fourth logic gate (32) depending on a third ground pair signal (S3), the fourth logic gate (32) generating a ground pair output signal (S _ OUT) depending on a signal at the supply voltage input, in particular and depending on the control signal (S _ EXT).

11. Switching device (1) according to one of the preceding claims, wherein the output signal of the filter element (22) of the differential stage (2) is additionally passed to the output stage (3) as a fourth ground pair signal (S4), the fourth logic gate (32) of the output stage (3) is implemented as an AND logic gate with inverting input or as a NOR logic gate, AND the ground pair output signal (S _ OUT) is additionally generated as a function of the fourth ground pair signal (S4).

12. The switching device (1) according to any one of the preceding claims, wherein an error condition caused by an error on the further supply voltage (VCC _ EXT) is identified.

13. The switching device (1) according to any one of the preceding claims, wherein the switching device (1) comprises a supply voltage protection stage (7) which generates the supply Voltage (VCC) depending on a signal level of a further supply voltage (VCC _ EXT), monitors a voltage level of the further supply voltage (VCC _ EXT), a voltage level within a valid range, in particular within +3.0V DC to +3.5V DC, resulting in a transfer of the further supply voltage (VCC _ EXT) to the supply Voltage (VCC), a voltage level outside the valid range resulting in an isolation between the further supply voltage (VCC _ EXT) and the supply Voltage (VCC).

14. A system with a switching device (1) according to one of the preceding claims, with a safety-relevant switching device and a frequency converter, characterized IN that a differential input signal (S _ DIFF _ IN) can be generated by the safety-relevant switching device, a control signal (S _ EXT) can be evaluated and driven by the frequency converter, and the output signal to ground (S _ OUT) can be used to interrupt the generation of the rotating field of the frequency converter.

15. System according to claim 14, wherein the control signal (S EXT) can be short-circuited to ground potential (GND) via at least one third switching element in the frequency converter,

and/or the bus driver module can be supplied with power via a ground output signal (S _ OUT) for transmitting a PWM signal for generating the frequency converter rotating field.

Technical Field

The present invention relates to a switching device and system for converting differential input signals.

Background

A switching device for converting a differential input signal into a ground output signal/ground-referenced output signal is known from US 2010/0327914 a 1.

Another prior art is known from US 2008/0025451 a 1.

Disclosure of Invention

It is an object of the invention to improve an electronic circuit arrangement.

According to the invention, this object is achieved by a switching device according to the features given in claim 1 and a system with a switching device according to the features given in claim 14.

In order to convert a differential input signal into a ground output signal with a control signal, it is an important feature of the invention that an error state/fault state, in particular an error state caused by an error in the level transition and/or the signal transmission time, is identified, the identified error state causing the ground signal to be switched off and additionally displayed on the control signal.

Advantageously, with a constant number of interface signals, a defined/defined state of the ground output signal can be established and time-optimized error correction/troubleshooting can be ensured.

Advantageously, according to the invention, it is possible to identify during operation: whether the information of the output signal always corresponds to the information on the input signal.

In addition, in the present invention, an error state due to an error in level conversion and/or signal transmission time is recognized, and the recognized error state causes the output signal to be turned off and additionally displayed on the pin of the control signal.

The invention therefore has the advantage that defined states of the output signal are generated with a constant number of interface signals and time-optimized error correction is possible.

In a further advantageous embodiment, the switching device comprises a differential stage which generates a first ground-pair signal from the differential input signal with a delay at a first signal transmission time t1, and an output stage which generates a ground-pair output signal from the first ground-pair signal and from the control signal, the switching device comprising a further differential stage which generates a second ground-pair signal from the differential input signal with a delay at a second signal transmission time t2, in particular wherein the second signal transmission time t2 is substantially smaller than the first signal transmission time t1, an evaluation stage which generates a third ground-pair signal from the first ground-pair signal and the second ground-pair signal taking into account the first signal transmission time t1 and the second signal transmission time t2, and a bidirectional communication stage which generates the control signal either from the third ground-pair signal or from the third ground-pair signal and at least one counterparty station, the output stage additionally passes the first ground-to-ground signal to the ground-to-output signal in accordance with the third ground-to-ground signal. A counterpart station is here understood to be a component which is in connection with the switching device and which exchanges information with the switching device.

Advantageously, both the second signal transmission time t2 and the second signal to ground may be used as references to be able to identify and communicate errors in the differential stage and to provide another switch-off possibility for the signal to ground output.

Advantageously, with a constant number of interface signals, a defined state of the ground output signal can be established and time-optimized error elimination can be guaranteed.

Advantageously, according to the invention, it can be recognized during operation whether the information of the output signal always corresponds to the information on the input signal.

In addition, in the present invention, an error state due to an error in level transition and/or signal transmission time is recognized, and the recognized error state causes the output signal to be turned off and additionally displayed on the pin of the control signal.

The invention therefore has the advantage that defined states of the output signal are generated with a constant number of interface signals and time-optimized error correction is possible.

In a further advantageous embodiment, the differential stage is referenced to ground by means of an optocoupler. The output signal of the optocoupler is conducted via the filter element. The first switching element passes the supply voltage to the first ground signal in dependence on the output signal of the filter element. The first signal propagation time t1 of the differential stage is composed of the sum of the switching times of the optocoupler and of the first switching element and the delay time of the filter element.

This advantageously ensures galvanic isolation between the differential input signal and the first counterpoise signal, the interference pulses and/or transients/transients, i.e. the most transient signal level variations in the differential input signal that are either intentionally (for example for testing electronic circuits) or unintentionally (for example due to interference radiation) coupled onto the actual useful signal are suppressed, and the first counterpoise signal can be used for conducting higher currents, in particular for powering other circuit components.

In a further advantageous embodiment, the further differential stage implements a second signal to ground by means of a further optocoupler. The second signal transmission time t2 of the other differential stage corresponds substantially to the switching time of the other optocoupler. This advantageously ensures galvanic isolation between the differential input signal and the second ground signal.

In a further advantageous embodiment, the evaluation stage evaluates the first and second ground signals via at least one first logic gate, in particular via an exclusive-or (XOR) logic gate. The output signal of the first logic gate is conducted via the further filter element. The other filter element has a delay time tf. The delay time tf is selected according to the first signal transmission time t1, the second signal transmission time t2 and the signal transmission time tolerance value td, in particular wherein the delay time tf is | t2-t1| + td. Advantageously, a deviation between the first and second ground signals in terms of signal transmission time and signal level can thus be determined.

In a further advantageous embodiment, the further filter element comprises an RC filter and a second logic gate, in particular an inverting logic gate. The nominal value of the RC filter is chosen to be tf-R C. The second logic gate digitizes the output signal of the RC filter and generates the output signal of the other filter element. In particular, the second logic gate is implemented in CMOS technology. Thereby, the setting/adjustment of the delay time tf can advantageously be performed in a cost-effective and space-saving manner.

In a further advantageous embodiment, the output signal of the further filter element corresponds to a third ground signal.

In a further advantageous embodiment, the output signal of the further filter element sets a memory element, in particular an RS flip-flop. The output signal of the third logic gate, in particular the WIRED-OR logic gate, resets the memory element. The third logic gate evaluates the first and second ground signals. The output signal of the memory element corresponds to a third signal to ground. Advantageously, the identified error state can thus be stored until both the level of the first and the level of the second ground signal are at ground potential.

In a further advantageous embodiment, the bidirectional communication stage comprises a communication interface, in particular an open-drain interface, which has a pull-up resistor to the supply voltage or to a further supply voltage. The control signal can be short-circuited to ground potential via the second switching element as a function of the third ground signal, in particular in antiphase. An interface can thereby advantageously be formed in which a bidirectional information flow is possible via only one signal.

In a further advantageous embodiment, the output stage comprises a fourth switching element and at least one fourth logic gate. The fourth switching element passes the first pair of ground signals to at least one supply voltage input of the fourth logic gate according to the third pair of ground signals. The fourth logic gate generates a pair-ground output signal from the signal at the supply voltage input and the control signal. Advantageously, a diversified redundancy shutdown of the ground output signal can thus be realized, wherein a diversified redundancy shutdown is to be understood as an equivalent multi-stage shutdown with different functional principles, which can place the ground output signal in a defined state depending on the control signal at the signal input of the fourth logic gate and the supply voltage input of the fourth logic gate.

In a further advantageous embodiment, the output signal of the filter element of the difference stage is additionally passed to the output stage as a fourth signal pair to ground. The fourth logic gate of the output stage is designed here as an AND logic gate with an inverting input or as a NOR (NOR) logic gate AND additionally generates a ground output signal as a function of the fourth ground signal. Advantageously, in this way, in particular without the delay times of the first and fourth switching elements, the ground output signal can be switched off quickly in a transmission-time-optimized manner.

In a further advantageous embodiment, an error state caused by an error at a further supply voltage is identified. Additional fault diagnosis can advantageously be provided in this way.

In a further advantageous embodiment, the switching device comprises a supply voltage protection stage which generates the supply voltage as a function of a signal level of the further supply voltage. The voltage level of the further supply voltage is monitored, wherein voltage levels within an effective range, in particular within +3V DC to +3.5V DC, result in the further supply voltage being passed on to the supply voltage, and voltage levels outside the effective range result in an isolation between the further supply voltage and the supply voltage. The switching device can thus advantageously be protected against disturbances introduced into the system via the supply voltage.

In a further advantageous embodiment, the system with the switching device has a safety-relevant switching device and a frequency converter. The differential input signal (S _ DIFF _ IN) may be generated by a safety-relevant switching device. The control signal (S EXT) can be evaluated and controlled by the frequency converter. The output signal to ground (S _ OUT) can be used to interrupt the generation of the rotating field of the frequency converter.

In a further advantageous embodiment, the control signal (S _ EXT) can be short-circuited to ground potential (GND) via at least one third switching element in the frequency converter.

In a further advantageous embodiment, the bus driver module for transmitting the PWM signal for generating the rotating field of the frequency converter can be supplied with voltage via the output signal to ground (S _ OUT).

Further advantages are given by the dependent claims. The invention is not limited to the combination of features of the claims. Other possible combinations of the features of the claims and/or of the individual claims and/or of the features of the description and/or of the drawings can be made possible for the person skilled in the art, especially if this object is set forth and/or is set forth by comparison with the prior art.

Drawings

The invention is described in detail below with reference to the accompanying drawings.

Detailed Description

Fig. 1 shows an external interface of the switching device (1). According to the invention, the switching device (1) has three external interfaces. The differential input signal (S _ DIFF _ IN) is received, converted, and output as a ground output signal (S _ OUT) IN accordance with the control signal (S _ EXT). The differential input signal (S _ DIFF _ IN) is here a symmetrically transmitted signal, i.e. transmitted using a pair of identical signal conductors.

Typically, an information signal is transmitted on a first signal conductor and a static reference signal or the same but inverted signal as the first signal conductor is transmitted as a reference on a second signal conductor. The differential voltage of the differential input signal (S _ DIFF _ IN) preferably lies IN a voltage range of-30V DC to +60V DC, IN particular wherein the switching means are capable of interpreting differential signal levels smaller than +5V DC as low levels and interpreting differential signal levels larger than +11V DC as high levels, and setting the output signal to ground (S _ OUT) IN dependence on these interpreted level states and IN dependence on the control signal (S _ EXT).

Fig. 2 shows a possible implementation of a switching device (1) according to the prior art. The switching device is further refined by being divided into a differential stage (2) and an output stage (3).

The differential stage (2) generates a first ground signal (S1) from the differential input signal (S _ DIFF _ IN). The first signal propagation time t1, i.e. the time required for a state change on the differential input signal (S _ DIFF _ IN) until it appears on the first ground signal (S1), is derived from the internal structure of the differential stage (2).

The output stage (3) provides a ground output signal (S _ OUT) at an output terminal for further application within the system. The state of the control signal (S _ EXT) determines whether the level of the first ground signal (S1) is reflected in the ground output signal (S _ OUT) or whether the ground output signal (S _ OUT) is pulled into a defined state, typically to Ground (GND).

Fig. 3 shows a switching device (1) according to the invention. In addition to the differential stage (2) and the output stage (3), the switching device (1) is further refined by adding a further differential stage (4), an evaluation stage (5) and a bidirectional communication stage (6).

Another differential stage (4) generates a second ground signal (S2) from the differential input signal (S _ DIFF _ IN). The second signal propagation time t2, i.e. the time required for a state change on the differential input signal (S _ DIFF _ IN) until it is displayed on the second ground signal (S2), results from the internal structure of the further differential stage (2). The internal structure of the further differential stage (2) is selected in particular such that the resulting second signal transmission time t2 is much shorter than the first signal transmission time t1 of the differential stage (2).

The evaluation unit (5) compares the first ground signal (S1) with the second ground signal (S2), and generates a third ground signal (S3) according to the comparison result.

This enables a test to be carried out which monitors the function of the differential stage (2) and, in the event of a deviation from the signal behavior of the further differential stage (4) as a reference, takes into account the first signal transmission time t1 and the second signal transmission time t2 and supplies this information in the switching device (1) to the further functional blocks.

In contrast to the prior art, the bidirectional communication stage (6) has an interface for the control signal (S _ EXT), which can process control information transmitted to the switching device (1) and reporting information from the switching device (1).

In addition to the prior art, the output stage (3) uses a third signal to ground (S3). Here, the states of the third ground signal (S3) and the control signal (S _ EXT) determine whether the level of the first ground signal (S1) is reflected in the ground output signal (S _ OUT), or whether the ground output signal (S _ OUT) is pulled to the ground potential (GND) in a defined state, in many cases.

Another embodiment of a switching device (1) according to the invention is shown in fig. 4. In addition to fig. 3, fig. 4 includes a power supply voltage protection stage (7) and a fourth signal to ground (S4).

The supply voltage protection stage (7) is connected upstream of the supply Voltage (VCC) input and monitors the actual supply voltage for operating the switching device (1), referred to as a further supply voltage (VCC _ EXT) here, for a useful voltage range. A voltage level of the further supply voltage (VCC _ EXT) within the effective voltage range results in the further supply voltage (VCC _ EXT) being transferred to the supply Voltage (VCC). A voltage level of the further supply voltage (VCC _ EXT) lying outside the effective voltage range results in the further supply voltage (VCC _ EXT) being isolated from the supply Voltage (VCC) and thus the supply Voltage (VCC) is set to a voltage-free state.

The no-voltage state causes both the output signal to ground (S _ OUT) and the control signal (S _ EXT) to be at or at least close to ground potential (GND). Furthermore, a fourth ground signal (S4) is generated in the differential stage (2), which is also additionally evaluated by the output stage (3).

The state of the third ground signal, the state of the fourth ground signal (S4) and the state of the control signal (S _ EXT) determine whether the level of the first ground signal (S1) is reflected in the ground output signal (S _ OUT) or whether the ground signal (S _ OUT) is pulled to a defined state, typically to Ground (GND). In particular, the supply voltage protection stage (7) is dimensioned such that a supply voltage level at least in the range of-0.5V DC to +15V DC can be applied at an input for receiving a further supply voltage (VCC _ EXT).

Furthermore, the generation and evaluation of the fourth ground signal (S4) is designed such that the ground output signal (S _ OUT) can be switched off quickly in a transmission-time-optimized manner.

An exemplary implementation of the switching device (1) according to the invention is depicted in fig. 5. Starting from fig. 4, the functional blocks of the differential stage (2), the output stage (3), the further differential stage (4), the evaluation stage (5) and the bidirectional communication stage (6) are further refined and a possible circuit implementation is shown.

IN the differential stage (2), the differential input signal (S _ DIFF _ IN) is evaluated by means of a photo coupler (21). The input end of the photoelectric coupler (21) is connected to the resistor voltage divider (24). At the output, the optocoupler (21) switches the supply Voltage (VCC) based on a (gegen) pull-down resistor (25). The output signal of the optocoupler (21) is conducted via a filter element (22) which consists of an RC filter and an inverting logic gate, in particular an inverting logic gate with a Schmitt trigger input.

The output signal of the inverting logic gate here simultaneously forms the output signal of the filter element (22) and is supplied as a fourth signal (S4) to ground to the downstream functional block. Furthermore, the output signal of the filter element (22) is used for driving a first switching element (23), which is embodied here as a PFET transistor, via a series resistor (26). The PFET transistor is capable of delivering a supply Voltage (VCC) to a plurality of downstream functional blocks via a first ground-to-ground signal (S1).

IN a further differential stage (4), the differential input signal (S _ DIFF _ IN) is evaluated by means of a further optocoupler (41). The input of the further optocoupler (41) is switched on via a further resistor divider (42). At the output, the other optocoupler (41) switches the supply Voltage (VCC) on the basis of the other pull-down resistor (43), and the output signal of the other optocoupler (41) is passed directly to the downstream functional block as a second ground signal (S2).

The evaluation stage (5) then compares the first ground signal (S1) with the second ground signal (S2) by means of a first logic gate (51), here embodied as an XOR logic gate.

The output of the first logic gate (51) is conducted via a further filter element (52) which consists of an RC filter (521) and a second logic gate (522), in particular a second inverting logic gate (522) with a schmitt trigger input. The output signal of the second logic gate (522) now simultaneously forms the output signal of the further filter element (52) and is used to actuate the setting input of the RS flip-flop (53). Further, the first ground signal (S1) and the second ground signal (S2) are logically operated with each other via a wire-OR circuit (54) composed of one diode each in a signal path leading to the respective signals, and are connected to the ground potential (GND) via a pull-down resistor.

The output signal of the WIRED-OR circuit is used to reset the RS flip-flop (53). The RS flip-flop (53) is preferably implemented such that its input is active low. Circuit embodiments designed in this way allow different voltage levels between the first (S1) and second (S2) ground signals present over a period of time t greater than a defined delay time tf derived from the selection of components of the RC filter to result in the setting of the RS flip-flop, and the RS flip-flop (53) can only be reset when the first (S1) and second (S2) ground signals are low, i.e. signal levels close to ground level (GND).

The output signal of the RS flip-flop (53) now simultaneously forms the output signal of the evaluation stage (5) and is supplied as a third ground signal (S3) to further downstream functional blocks.

The bidirectional communication stage (6) then uses the third pair of ground signals (S3) in order to drive a second switching element (63), here implemented as an NFET transistor, via a series resistance (64). The NFET transistor forms, in cooperation with an additional pull-up resistor (62) connected to a supply Voltage (VCC), a communication interface (61) (here embodied as an open-drain interface) capable of pulling the control signal (S EXT) to Ground (GND) in response to a third pair of ground signals (S3). Thus, both the bidirectional communication stage (6) and the optionally connected counterpart station can pull the control signal (S _ EXT) to a low level. If neither the bidirectional communication stage (6) nor the opposite station actuates the signal (S _ EXT), the signal (S _ EXT) is always set to a high level by means of a pull-up resistor (62).

The output stage (3) also uses the third pair of ground signals (S3) to drive a fourth switching element (31), here implemented as a PFET transistor, via a series resistance (33). The PFET transistor is now able to transmit the first ground signal (S1) AND thus the supply Voltage (VCC) to a supply voltage input of a fourth logic gate (32), here implemented as an AND logic gate with an inverting input. Meanwhile, the power supply voltage input terminal of the AND logic gate is connected to the ground potential (GND) via a pull-down resistor (34). The control signal (S _ EXT) drives a fifth switching element (35), which is embodied as an NFET transistor. The NFET transistor switches Ground (GND) based on a pull-up resistor (36) which also relates to the supply voltage input of the AND logic gate.

With this transistor circuit, the voltage level on the control signal (S _ EXT) is inverted AND connected to one of the inverting input terminals of the AND logic gate. The other inverting input terminal of the AND logic gate is connected to the fourth pair of ground signals (S4). The output signal of the AND logic gate here simultaneously forms the output signal of the output stage (3) AND thus also the ground output signal (S _ OUT) of the switching device (1) according to the invention.

With this circuit configuration, the output stage (3) can rapidly switch off the ground output signal (S _ OUT) depending on the fourth ground signal (S4) and the control signal (S _ EXT) by means of the fourth logic gate (32). Depending on the parasitic residual capacitance when the supply voltage which has to be discharged first is switched off, a slow switching off of the diversity redundancy of the ground output signal (S _ OUT) is additionally caused by the first ground signal (S1) and the third ground signal (S3). By switching off the supply voltage, however, it can be ensured that the ground output signal (S _ OUT) is switched off even if the fourth logic gate (32) fails.

The control signal (S _ EXT) can be used in particular for controlling the output stage (3).

The control signal (S _ EXT) according to the invention is generated not only by the bidirectional communication stage (6) but also by a counterpart station optionally connected to the switching device (1).

In the exemplary embodiment according to fig. 5, a high level of the control signal (S _ EXT) means that the output stage (3) is turned on/enabled, and a low level of the control signal (S _ EXT) means that the output stage (3) is blocked.

Here the low level dominates. A high level is only detected on the signal (S _ EXT) when the communication stage (6) and the opposite station jointly switch on the output stage (3).

If the opposite station wants to switch on the output stage (3), but measures a low level, the opposite station can deduce therefrom: the switching device (1) is in an error state.

It is to be noted again that the output stage (3) evaluates the signal (S _ EXT) in order to accordingly reflect the first ground-to-ground signal (S1) on the ground-to-ground output signal (S _ OUT) or to pull the ground-to-ground output signal (S _ OUT) into a defined state, typically to ground potential (GND), while the signal (S _ EXT) is generated by the bidirectional communication stage (6) in conjunction with a counter-station optionally connected thereto.

The following also applies to this: in contrast to the prior art, the bidirectional communication stage (6) has an interface for the control signal (S _ EXT), which can process both control information transmitted to the switching device (1) and reporting information from the switching device (1).

Therefore, in the present embodiment: the bidirectional communication stage (6) then uses the third pair of ground signals (S3) to drive a second switching element (63), here implemented as an NFET transistor, via a series resistance (64). The NFET transistor forms, in cooperation with an additional pull-up resistor (62) connected to a supply Voltage (VCC), a communication interface (61), here embodied as an open-drain interface, which is capable of pulling the control signal (S EXT) to ground potential (GND) in dependence on a third ground-pair signal (S3). Thus, both the bidirectional communication stage (6) and the partner station optionally connected thereto can pull the control signal (S _ EXT) to a low level. If neither the bidirectional communication stage (6) nor the opposite station actuates the signal (S _ EXT), the pull-up resistor (62) sets the signal (S _ EXT) to a high level at all times.

The following list of reference numerals is incorporated into the specification and illustrates other features of the invention.

List of reference numerals:

1 switching device

2 differential stage

21 photoelectric coupler

22 filter element

23 first switching element

24-resistor voltage divider

25 pull-down resistor

26 series resistance

3 output stage

31 fourth switching element

32 fourth logic gate

33 series resistance

34 pull-down resistor

35 fifth switching element

36 pull-up resistor

4 another differential stage

41 another photocoupler

42 another resistor divider

43 another pull-down resistor

5 evaluation level

51 first logic gate

52 Another filter element

521 RC filter

522 second logic gate

53 memory element

54 third logic gate

6 bidirectional communication stage

61 communication interface

62 pull-up resistor

63 second switching element

64 series resistance

7 power supply voltage protection stage

GND ground potential

Duration of t

t1 first Signal Transmission time

t2 second Signal Transmission time

td signal transmission time tolerance value

tf delay time

S1 first ground signal

S2 second ground signal

S3 third ground signal

S4 fourth ground signal

S _ DIFF _ IN differential input signal

S _ EXT control signal

S _ OUT output signal to ground

VCC supply voltage

VCC _ EXT another supply voltage