DE102018114861A1 - Active filter for filtering common mode interference - Google Patents

Abstract

The invention relates to an active filter (1) for suppressing common mode interference in a two-pole transmission line (3) for differential signals, the active filter (1) being galvanically connected to the two transmission lines (31, 32) in order to create a simply constructed filter It is proposed that it can be produced inexpensively that two current mirrors (21, 22) connected in parallel are each connected between the positive transmission line (31) and the negative transmission line (32), each of these two current mirrors forming a low-impedance discharge path for either positive or negative common-mode interference ,

Description

The invention relates to an active filter for suppressing common mode interference according to the features of the preamble of claim 1.

In practice, passive components are generally used to suppress common mode interference. In particular, frequency-dependent networks consisting of chokes and capacitors are used. However, these have the disadvantage that, depending on the frequency range to be filtered, the components have a large volume and are relatively expensive to manufacture.

In document EP 2 814 215 A1 describes an active filter for suppressing common mode interference in a signal transmission path between the transmitter and the receiver, the signal transmission path being electrically isolated via capacitors. The signal transmission path has a positive and a negative signal line, the active filter being connected to these two signal lines. The active filter has MOSFET transistors which are connected in such a way that they keep the voltage on the signal lines constant. For this purpose, the gate drive of the MOSFET transistors has a crossed feedback path, which contains a frequency-dependent network, in order to improve the signal transmission behavior of the active filter.

The US 2006/0251188 A1 shows a circuit for signal transmission in an Ethernet. To suppress common mode interference, active filters are also provided here, in which integrated amplifier circuits are used.

The document DE 100 21 928 A1 describes current mirrors in which an input current in a current sink is converted nonlinearly into a voltage, the voltage being used to control a further additional current source with essentially the same transmission characteristic. The circuit used for this essentially consists of several MOSFETs and, under certain conditions, is also suitable as an active filter for suppressing common mode interference. However, this circuit has separate inputs and outputs and can therefore not be used for bidirectional or direction-independent filtering in transmission lines.

The object of the present invention is to provide an active filter for the suppression of common mode interference, which can be used in differential signal transmissions. The active filter should be simple and inexpensive to manufacture. In particular, the active filter should be able to be used regardless of the direction, can be used in addition or as a replacement for a choke and should enable good interference suppression with a simple circuit design.

This object is achieved according to the invention by an active filter with the features of claim 1.

According to the invention, the active filter is designed to suppress common mode interference in a transmission path with a first transmission line and a second transmission line, the active filter being electrically connected to the two transmission lines. It is essential that two current mirror circuits connected in parallel are connected between the first transmission line and the second transmission line and each of these two current mirror circuits has at least one current mirror which is connected to a derivative or a center voltage line or a ground line in order to avoid common mode interference via the derivative or the center voltage line or to derive the ground line. The derivative is preferably a common line which has a defined potential. The defined potential of the derivation can be determined, for example, via an external power supply. In particular, the derivation serves to discharge interference currents or interference voltages.

A signal transmission line between a transmitter and a receiver is regarded as the transmission path, via which useful signals are transmitted between the transmitter and receiver. By inserting the two parallel current mirror circuits directly between the first transmission line and the second transmission line, bidirectional or direction-independent filtering is achieved. The active filter is preferably designed as a bidirectional filter. That is, the active filter suppresses interference signals, regardless of their direction of propagation or origin.

In conventional filter circuits, the inputs and outputs are separated, so that the direction of the signals and thus the filtering of the interference signals is fixed in a single direction, or a specific frequency response is specified. The parallel connection of the two current mirror circuits results in direction-independent or bidirectional interference signal suppression. This efficiently suppresses the propagation of interference signals on the transmission path or the transmission line.

In the case of signal transmission using the push-pull method (differential mode), the signals are push-pull, ie inverted (by 180 °) via two separate signal lines or transmission lines out of phase). The signal is thus transmitted via two transmission lines, that is to say via a first transmission line or positive transmission line and a second transmission line or negative transmission line. The receiver evaluates the difference between the two signals. If interference occurs due to induction or external electromagnetic fields, this interference occurs evenly in the two signal lines, ie not out of phase (common mode interference or CM, i.e. common mode) and is generally eliminated in the receiver. To prevent these common mode interference (CM interference) from spreading over the signal line, additional filters are used to suppress common mode interference (CM filter).

In particular, it can be provided in one embodiment that the first current mirror circuit forms a derivation path for positive common mode interference and the second current mirror circuit forms a derivation path for negative common mode interference. As a result, the active filter preferably forms a discharge path for interference signals of any polarity with low impedance, and a high-impedance path for the useful signals. The signal transmission of the useful signal is thus impaired as little as possible with efficient interference signal suppression.

The two current mirrors connected in parallel are preferably arranged symmetrically to one another. This ensures that interference signals can be filtered that are present on both the input and output side.

In particular, the two current mirror circuits are each driven by the same transmission line. Either the two current mirror circuits are driven jointly by the first transmission line, or the two current mirror circuits are jointly driven by the second transmission line.

It can preferably be provided that each of the two current mirror circuits is designed as a three-pole, each three-pole having an input, an output and a discharge or center voltage connection, and the input and the output of the three-pole are each connected to one of the transmission lines and the Lead connector is connected to the lead connector of the other tripole to form the common lead. The operating principle is as follows: A current at the input, pole "IN", flows due to the operating principle of the current mirror circuit at the same level and polarity at the output, pole "OUT". Due to the node condition, a leakage current then flows through the “COM” discharge connection pole. The internal structure of the current mirror circuit can vary as long as the current mirror circuit fulfills the structure and function described. Current mirror circuits such as Widlar, Kaskode, Wilson, etc., which are known to the person skilled in the art, can be used as current mirror circuits of the triple pole.

In one exemplary embodiment, it can be provided that each of the two current mirror circuits each has at least two transistors connected to one another, each of which forms a current mirror with a transmission ratio of 1. The use of a gear ratio of 1 enables the use of a simple circuit structure with efficient signal suppression at the same time.

Bipolar transistors or FET (field effect) transistors or MOS-FETs (metal oxide semiconductor field effect transistor) or J-FETs (junction field effect transistor), or HEMTs (high-electron mobility transistor) can be used as transistors. The active filter can be at least partially designed as a discrete filter with discrete transistors. As an alternative or in addition, the active filter can also have integrated semiconductors or integrated circuits, for example ICs.

In particular, the two current mirror circuits are constructed symmetrically. The circuit structure of the two current mirror circuits can in principle be the same. In particular, the symmetrically constructed circuit has both a p-doped current mirror, that is to say a current mirror comprising at least two p-doped transistors, and also an n-doped current mirror connected in parallel thereto, that is to say a current mirror of the at least two n-doped transistors includes. Thus, the first current mirror circuit can have, for example, only N-type transistors with basically the same structure and the second current mirror circuit can only have P-type transistors, or vice versa.

In one possible embodiment, the current mirrors can have field-effect transistors. For example, the two current mirrors each have at least two field-effect transistors connected to one another and the first current mirror has two N-type field-effect transistors, preferably N-MOSFET, and the second current mirror has two P-type field-effect transistors, preferably P-MOSFET. The use of field effect transistors has the advantage that they have a very high input resistance, so that the signal present at the input, for example at the drain connection, can be passed on with as little loss as possible and largely unchanged.

The source connections of the four field effect transistors can be connected to a common, externally applied center voltage. This serves as a derivation path for the common mode faults. The center voltage is preferably at the quiescent potential of the transmission lines, ie the first transmission line or the second transmission line. Alternatively, the center voltage can also have a potential which lies between the potentials of the transmission lines. In systems with a symmetrical supply voltage, the center voltage can form the ground potential, for example.

The drain connections of two of the field effect transistors can be connected to the first transmission line and the drain connections of the two further field effect transistors can be connected to the second transmission line.

In this case, for example, all the gate connections of the four field effect transistors can be connected to one another and either connected to the same first transmission line or to the same second transmission line. Thus, the two current mirror circuits are driven by the same transmission line.

It can advantageously be provided that the gate connections of the four field effect transistors are directly connected to one another and are connected to the same first transmission line or to the same second transmission line via a resistor. The resistance can also be formed or replaced by a frequency-dependent reactance network. The frequency-dependent reactance network allows a specific frequency behavior of the active filter to be set in a targeted manner.

In an alternative embodiment it can be provided that the two current mirrors each have two bipolar transistors connected to one another. For example, the first current mirror can have npn transistors and the second current mirror can have pnp transistors. The use of bipolar transistors has the advantage that there are no interfering gate-source and gate-drain capacitances and thus a faster switching of the transistors at high frequencies of the input signal can be guaranteed.

It can be provided here that the emitter connections of the four bipolar transistors are connected to a common derivative or a center voltage. In this embodiment, too, the center voltage serves as a discharge path for the common-mode currents. The center voltage is preferably at the quiescent potential of the first transmission line or the second transmission line. Alternatively, the center voltage can also have a potential which lies between the potentials of the transmission lines. In systems with a symmetrical supply voltage, the center voltage can form the ground potential, for example.

It can further be provided that the collector connections of two of the bipolar transistors are connected to the first transmission line and the collector connections of the two further bipolar transistors are connected to the second transmission line.

Furthermore, all base connections of the four bipolar transistors can be connected to one another and connected either to the same first transmission line or to the same second transmission line. This ensures that the two current mirror circuits are each driven by the same transmission line.

The mode of operation of the embodiment using bipolar transistors is basically the same as that using field-effect transistors or MOSFETs. However, the base current of the bipolar transistors with the same current gain causes an error which causes an undesired differential mode signal. This error is caused by the fact that a base current flows when using bipolar transistors. This can lead to a falsification of the signal to be transmitted, since the output signal is directly influenced and changed by the base current.

In order to avoid this error, it can advantageously be provided in one embodiment that the base connections of the two bipolar transistors of a current mirror are directly connected to one another and the base current of a current mirror is controlled either by the first or the second transmission line via an intermediate bipolar transistor or field-effect transistor. The insertion of a further bipolar transistor to provide the base current is known to the person skilled in the art as a cascode current mirror. In addition to the cascode current mirror, there are other improved current mirror circuits (e.g. Wilson current mirror) that solve the described problem of the base current.

If a field effect transistor is inserted, its gate connections are directly connected to one another, and either directly or via a resistor, preferably via a frequency-dependent reactance network, to the same first Transmission line or the same second transmission line connected.
By using a resistor, preferably a frequency-dependent reactance network, the system described can be stabilized or the frequency behavior can be set in a targeted manner.

The described embodiments of an active filter are preferably used in a circuit arrangement for signal transmission with a transmitter and a receiver and an intermediate signal transmission line, comprising a first transmission line and a second transmission line for the transmission of push-pull signals, an active filter between the first transmission line and the second transmission line is switched according to one of the embodiments described above for the suppression of common mode signals.

In one embodiment it can be provided that the signal transmission line between the transmitter and the receiver is galvanically isolated. The galvanic isolation can take place by an optical coupling, or an inductive coupling, or by a capacitive coupling. The galvanic isolation can ensure that only AC signals are fed into the active filter, while DC signals cannot bridge the galvanic isolation.

In particular, it can be provided that the signal transmission line connected to the transmitter has a different voltage level, ie a higher voltage level or a lower voltage level than the signal transmission line directly connected to the receiver.

The active filter is preferably looped into the signal line directly connected to the receiver and is operated at the voltage level of the receiver signal line.

Alternatively, the active filter can be looped into the signal line directly connected to the transmitter and operated at the voltage level of the transmitter signal line.

Thus, the active filter can be operated at a suitable voltage level and transmission paths can also be filtered, the voltage level of which deviate from the specifications of the transistors used.

It is advantageous that the active filter according to the invention works bidirectionally and can therefore also be used in a bidirectional transceiver system. It is thus possible to use the active filter according to the invention for signal transmissions in alternating operation or in the half-duplex method. For this purpose, it can be provided that the circuit arrangement for signal transmission has two transmitter and receiver pairs, which are connected via a signal transmission line in such a way that bidirectional signal transmission takes place in duplex or half-duplex operation, the active filter being designed as a bidirectional active filter and into which Signal transmission line is looped in between the first transmission line and the second transmission line.

• 1: Eine Schaltungsanordnung mit einem kapazitiv gekoppelten Übertragungspfad der einen erfindungsgemäßen CM-Filter aufweist;
• 2: Eine Umsetzung des erfindungsgemäßen CM-Filters durch Verschaltung von zwei Stromspiegeln;
• 3: Einen erfindungsgemäßen CM-Filter in einer Ausführungsform mit MOSFET Transistoren;
• 4: Einen erfindungsgemäßen CM-Filter in einer Ausführungsform mit bipolar-Transistoren;
• 5: Einen erfindungsgemäßen CM-Filter in einer Ausführungsform mit bipolar-Transistoren und vorgeschalteten MOSFETs
• 6: Einen erfindungsgemäßen CM-Filter in einer Ausführungsform mit bipolar-Transistoren und vorgeschalteten MOSFETs mit Widerstand im Gate-Kreis;
• 7: Einen erfindungsgemäßen CM-Filter in einer Ausführungsform mit MOSFETs und mit Widerstand im Gate-Kreis;

Further refinements of the invention are described in the figures and the following description of the figures. Show:

• 1 : A circuit arrangement with a capacitively coupled transmission path which has a CM filter according to the invention;
• 2 : Implementation of the CM filter according to the invention by connecting two current mirrors;
• 3 : A CM filter according to the invention in one embodiment with MOSFET transistors;
• 4 : A CM filter according to the invention in one embodiment with bipolar transistors;
• 5 : A CM filter according to the invention in one embodiment with bipolar transistors and upstream MOSFETs
• 6 : A CM filter according to the invention in one embodiment with bipolar transistors and upstream MOSFETs with resistance in the gate circuit;
• 7 : A CM filter according to the invention in one embodiment with MOSFETs and with resistance in the gate circuit;

In the 1 to 7 different configurations of the active filter according to the invention are shown. The same or equivalent components are provided with the same reference symbols. In the respective description of the figures, the differences between the individual embodiments are dealt with without the common circuit components being repeated in detail. The basic operating principle of the active filter is the same in all of the exemplary embodiments shown.

It is clear to the person skilled in the art that the exemplary embodiments described are not exhaustive. For example, the described advantages of the individual exemplary embodiments can be combined with one another without departing from the scope of the invention.

The 1 shows a circuit arrangement for signal transmission 9 with a transmitter 11 and a receiver 12 , Between the transmitter 11 and the recipient 12 is a transmission path 3 arranged with a first transmission line and a second transmission line. Symmetrical push-pull signals (DM differential mode) are transmitted via the transmission path. The signals can be analog signals or digital signals. The transmission path between transmitters 11 and receiver 12 has a galvanic isolation 7 by means of capacitors. In the receiver-side transmission path 3 is an active filter according to the invention 1 looped. If the transmission path is long, several active filters can also be used 1 parallel in the transmission path 3 be looped in. Also a combination of the active filter 1 with additional passive filter networks in the transmission path is possible in order to obtain improved interference signal filtering.

In the 2 is a schematic diagram of the CM filter according to the invention 1 in a transmission line 3 shown. The transmission line 3 has a first transmission line 31 and a second transmission line 32 on. There are two current mirrors between these two transmission lines 21 . 22 arranged. The current mirror 21 . 22 are each as a three-pole 4 . 4 ' trained and among themselves via the common derivative 44 , or the medium voltage line V _mid connected. Each of the current mirrors 21 . 22 has an entrance 41 , an exit 42 and one with the common derivative 44 connected discharge connection 43 on. For everyone the current mirror 21 . 22 applies: A current at the entrance 41 , Pole "IN" flows due to the functioning of the current mirror 21 respectively. 22 at the same height and polarity at the output 42 , Pole "OUT". A leakage current then flows through the leakage connection due to the node condition 43 , Pole "COM". The internal structure of the current mirror circuit 21 respectively. 22 is variable. Current mirror circuits such as Widlar, Kaskode, Wilson, etc., known to those skilled in the art, can be used as current mirror circuits.

The 3 shows a possible embodiment of the invention. It is a circuit diagram of an active filter 1 to suppress common mode noise using MOSFETs NMOS1 . NMOS2 . PMOS1 . PMOS2 using a current mirror 2 , The active filter 1 is between the first transmission line 31 and the second transmission line 32 a transmission path 3 (as in 1 visible) looped. It has a current mirror 2 consisting of two symmetrical current mirror circuits connected in parallel 21 . 22 on. Each of these current mirror circuits 21 . 22 either assigns a pair NMOS transistors NMOS1 . NMOS2 , or a pair of PMOS transistors PMOS1 . PMOS2 on. Each transistor pair forms a current mirror 21 . 22 with a transmission ratio k _I = 1.

The transmission line 3 has a galvanic isolation 7 (as in 6 or 7 outlined) by means of two capacitors 71 . 72 on. These capacitors 71 . 72 disconnect the DC circuit on the transmitter side of the transmission line 3 from the receiving end. However, as a result of displacement currents, common mode interference can be passed on via these capacitors, by means of the active filter 1 be suppressed.

The two current mirrors 21 . 22 are on a common signal line 31 driven. This is the first transmission line 31 , For this purpose, all gates are in the same way with this transmission line 31 connected. Alternatively, the control could also be via the second transmission line 32 respectively.

The MOSFETs are on the source side NMOS1 . NMOS2 . PMOS1 . PMOS2 with an externally applied center voltage V _mid connected, which serves as a derivation or derivation path for the interference signals. The center tension V _mid can be provided, for example, by an external voltage supply or can be derived in a known manner from a supply voltage. The center voltage can be between the potential of the first transmission line 31 V _{RX +} and the second transmission line 32 V _RX- lie, for example in the middle.

Between the first transmission line 31 and the second transmission line 32 are also working resistances R1 . R2 connected. These resistors serve to stabilize the operating point by compensating currents can be derived through the resistors.

The drain connections of the MOSFETs NMOS1 . NMOS2 . PMOS1 . PMOS2 are in pairs NMOS1 . PMOS1 or NMOS2 . PMOS2 with a transmission line 31 or 32 connected.

The general functioning of the active filter can be described as follows:

$$I_{rx-}=I_{CMrx-}+I_{DMrx-}$$

The one over the first transmission line 31 transmitted currents are called I _{rx +} and the currents transmitted over the second transmission line are called I _rx- designated. About the isolation capacitors 71 . 72 insulation capacities are provided, which with C _iso be designated. The streams I _{rx +} and I _rx- can both from a common mode (CM) portion I _CM , as well as a differential mode (DM) component I _DM consist. $$I_{rx+}=I_{CMrx+}+I_{DMrx+}$$

$$I_{rx-}=I_{CMrx-}+I_{DMrx-}$$

$$I_{DMrx+}=-I_{DMrx-}$$

Are the insulation capacities C _iso The same applies in both signal lines: $$I_{CMrx+}=I_{DMrx-}$$

$$I_{DMrx+}=-I_{DMrx-}$$

Is the stream I _{rx +} be positive NMOS1 and NMOS2 modulated. is U _th > 0, is NMOS1 in the constriction area, there U _DS = U _GS , In general, the following applies to a MOSFET in the pinch area $$I_D=\frac{K}{2}{\left(U_{GS}-U_{tH}\right)}^2\left(1+\frac{U_{DS}}{U_A}\right)$$

I_D:

Drainstrom

U_GS:

Gate-Source Spannung

U_DS:

Drain-Source Spannung

U_th:

Schwellenwertspannung

U_A:

Ausgangsspannung

K:

Kennlinienparameter

The following applies:

I _D :

drain current

U _GS :

Gate-source voltage

U _DS :

Drain-source voltage

U _th :

Threshold voltage

U _A :

output voltage

K:

Characteristic parameters

The voltage drop between the first transmission line 31 and the center voltage can be neglected the resistances R ₁ and R ₂ , and the channel length modulation can be calculated as follows: $$U_{DS}=U_{GS}=\sqrt{\frac{2I_D}{K}+U_{tH}}$$

Is also I _rx- > I _{rx +} , is located NMOS2 also in the constriction area, but can not more than NMOS1 wear. The excess stream which 2I _DMrx - corresponds, must now either over the resistance R ₂ drain, or when flowing via the MOSFETs, by channel length modulation, generates a significantly higher voltage drop than the CM current components.

The differential voltage drop, U _DM , between the first transmission line 31 and the second transmission line 32 therefore admits: $${\text{U}}_{\text{DM}}=2{\text{I}}_{\text{<figure-callout id="2" label="DM R" filenames="DE102018114861A1\_0008.png,DE102018114861A1\_0009.png" state="{{state}}">DM </figure-callout>}}\frac{R_{}}{}\frac{{}_2\mathrm{*}{r}_{\mathrm{<figure-callout\; id="2"\; label="D\; S\; R"\; filenames="DE102018114861A1\_0008.png,DE102018114861A1\_0009.png"\; state="\{\{state\}\}">D\; </figure-callout>}S}}{R_{}}$$

r_DS:

Drain-Source Widerstand

The following applies:

r _DS :

Drain-source resistance

The two resistors R1 and R2 are optional there r _DS however, depending on the working point, they help stabilize the system. Is the stream I _rx- < I _{rx +} is located NMOS2 no longer in the pinch-off area, but in the ohmic area. The voltage drop across U _DS of NMOS2 is significantly lower than that of the NMOS1 , So it can DM Signal continues to be transmitted.

Is the stream I _{rx +} now negative, the current is no longer over the NMOS , but about the PMOS - drain the current mirror. The basic functionality remains the same.

The 4 shows another possible embodiment of the invention. It is a circuit diagram of the active filter 1 to suppress common mode interference using bipolar transistors NPN1 . NPN2 . PNP1 . PNP2 , Again, there are two symmetrical current mirror circuits 21 . 22 connected in parallel and in the transmission path 3 looped. Here, the current mirror include 21 . 22 four bipolar transistors NPN1 . NPN2 . PNP1 . PNP2 , The base connections of both transistors NPN1 . NPN2 or PNP1 . PNP2 the current mirror 21 or 22 are common to the same first transmission line 31 connected and are controlled by this together. Alternatively, the current mirror could be controlled 21 . 22 also via the second transmission line 32 respectively.

The emitter connections of the bipolar transistors NPN1 . NPN2 . PNP1 . PNP2 are all with a common derivative or a center voltage V _mid connected. Via the common derivative or center voltage V _mid the common-mode currents of the interference signals are derived.

The collector connections of two of the bipolar transistors NPN1 and PNP1 are with the first transmission line 31 connected. The collector connections of the other bipolar transistors PNP1 and PNP2 are with the second negative signal line 32 connected.

5 shows another possible embodiment of the active filter 1 to suppress common mode interference. Here are bipolar transistors NPN1 . NPN2 . PNP1 . PNP2 used. In order to compensate for the voltage errors that occur with bipolar transistors, the current mirror is used in the base circuit 21 . 22 upstream MOSFETs 73 used. This has the effect of compensating for the error that occurs in bipolar transistors with the same power supply. This is in addition to that already in 2 shown circuit diagram each a MOSFET 73 between the bases of the transistors NPN1 . NPN2 respectively. PNP1 . PNP2 and the signal line 31 connected. Thus the base currents of the bipolar transistors NPN1 . NPN2 . PNP1 . PNP2 now about MOSFETs 73 controlled. The power supply of the intermediate MOSFETs 73 occurs through externally applied voltages V _DD respectively V _SS ,

The 6 and 7 show an example of the addition of the circuits described in the control circuit or in the base circuit or source circuit by a resistor R _v , In the 6 is the active filter 1 based on bipolar transistors NPN1 . NPN2 . PNP1 . PNP2 similar to the embodiment of 5 built up. Here is the resistance R _v in the source circuit of the intermediate MOSFETs 73 looped.

In the 7 is the active filter 1 based on MOSFETs NMOS1 . NMOS2 . PMOS1 . PMOS2 according to the embodiment of 3 built up. Here is a reactance R _v or a resistance R _v directly into the source circuit of the two current mirror circuits 21 . 22 looped. By inserting one or more additional reactances or resistors R _v , the properties of the active filter 1 , for example the frequency response or the impedance in the control path.

The invention is not restricted to the embodiments shown. In particular, the properties of the active filter, for example frequency-dependent behavior or the impedance in the control path, can be influenced in that the control of the current mirror circuits either by the series resistor shown R _v and / or through a corresponding frequency-dependent network. In addition, other embodiments of the current mirror circuits known from the literature to the person skilled in the art, for example cascode or Wilson current mirrors, are possible.

LIST OF REFERENCE NUMBERS

1

Active filter

11

Channel

12

receiver

2

current mirror

21

first current mirror circuit

22

second current mirror circuit

3

Signal transmission line

31

first or positive transmission line

32

second or negative transmission line

V _mid

center voltage

4, 4 '

three pole

41

Entrance in

42

Output, OUT

43

Drain connection, COM

44

common derivation

7

galvanic isolation

71

isolating capacitor

72

isolating capacitor

73

upstream MOSFET

R1

resistance

R2

resistance

Rv

resistance

NMOS1

N-type MosFET

NMOS2

N-type MosFET

PMOS1

P-type MosFET

PMOS2

P-type MosFET

npn1

N-bipolar transistor

npn2

N-bipolar transistor

pnp1

P-bipolar transistor

pnp2

P-bipolar transistor

9

Circuit arrangement for signal transmission

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• EP 2814215 A1 [0003]
• US 2006/0251188 A1 [0004]
• DE 10021928 A1 [0005]

Claims (19)

Active filter for suppressing common mode interference in a transmission path with a first transmission line (31) and a second transmission line (32), the active filter (1) being galvanically connected to the two transmission lines (31, 32), characterized in that between the the first transmission line (31) and the second transmission line (32) are connected two current mirror circuits (21, 22) connected in parallel and each of these two current mirror circuits (21, 22) has at least one current mirror which has a common derivative (44) or a center voltage line (V _mid ) or is connected to a ground line in order to derive common-mode interference via the common lead (44) or the medium voltage line (V _mid ) or the ground line. Active filter after Claim 1 , characterized in that the first current mirror circuit (21) forms a derivative path for positive common mode interference and the second current mirror circuit (22) forms a derivative path for negative common mode interference. Active filter after Claim 1 or 2 , characterized in that each of the two current mirror circuits is designed as a three-pole (4), each three-pole (4) having an input (41) an output (42) and a derivative connection (43), and in each case the input (41) and the output (42) of the triple pole (4, 4 ') is connected to one of the transmission lines (31, 32) and the lead connection (43) is connected to the lead connection (43) of the other triple pole (4', 4), preferably that the two interconnected lead connections (43) are connected to the common lead (44) or the medium voltage line (V _mid ). Active filter according to one of the Claims 1 to 3 , characterized in that each of the two current mirror circuits (21, 22) each has at least two interconnected transistors which each form a current mirror with a transmission ratio of 1, preferably that the first current mirror circuit (21) has only N-type transistors and the second Current mirror circuit (21) has only P-type transistors. Active filter according to one of the preceding claims, characterized in that the two current mirror circuits (21, 22) each have at least two field effect transistors connected to one another, in particular J-FET's or MOS-FET's or HEMT's, wherein it is preferably provided that the first current mirror circuit has two N -type field-effect transistors, preferably N-MOSFET (NMOS1, NMOS2), and the second current mirror has two P-type field-effect transistors, preferably P-MOSFET (PMOS1, PMOS2). Active filter after Claim 5 , characterized in that the source connections of the four field effect transistors (NMOS1, NMOS2, PMOS1, PMOS2) are connected to the common derivative, preferably a common center voltage line (V _mid ). Active filter after Claim 5 or 6 , characterized in that the drain connections of two of the field effect transistors (NMOS1, PMOS1) are connected to the first transmission line (31) and the drain connections of the two further field effect transistors (NMOS2, PMOS2) are connected to the second transmission line (32). Active filter according to one of the Claims 5 to 7 , characterized in that all gate connections of the four field effect transistors (NMOS1, NMOS2, PMOS1, PMOS2) are connected to one another and are either connected to the same first transmission line (31) or to the same second transmission line (32). Active filter according to one of the Claims 5 to 8th , characterized in that the gate connections of the four field effect transistors (NMOS1, NMOS2, PMOS1, PMOS2) are directly connected to one another and via a resistor, preferably via a frequency-dependent resistance network or reactance network, to the same first transmission line (31) or to the same second transmission line (31) are connected. Active filter according to one of the Claims 1 to 4 , characterized in that the two current mirror circuits (21, 22) each have two interconnected bipolar transistors and the first current mirror circuit (21) has two npn transistors (npn1, npn2) and the second current mirror (22) has two pnp transistors (pnp1, pnp2). Active filter after Claim 10 , characterized in that the emitter connections of the four bipolar transistors (npn1, npn2, pnp1, pnp2) are connected to a common center voltage line (V _mid ). Active filter according to one of the Claims 10 or 11 , characterized in that the collector connections of two of the bipolar transistors (npn1, pnp1) are connected to the first transmission line (31) and the collector connections of the two further bipolar transistors (npn2, pnp2) are connected to the second transmission line (32). Active filter according to one of the Claims 10 to 12 , characterized in that all base connections of the four bipolar transistors (npn1, npn2, pnp1, pnp2) are connected to one another and are either connected to the same first transmission line (31) or to the same second transmission line (32). Active filter according to one of the Claims 10 to 13 , characterized in that the base connections of the two bipolar transistors of a current mirror (21 or 22) are directly connected to one another and the base current of a current mirror is controlled either by the first transmission line (31) or the second transmission line (32) via an interposed field effect transistor (73) becomes. Active filter after Claim 14 , characterized in that the gate connections of the interposed field effect transistors (73) are directly connected to one another, and either directly, or via a resistor (R _v ), preferably via a frequency-dependent resistance network or reactance network, either with the same first transmission line (31) or are connected to the same second transmission line (32). Circuit arrangement for signal transmission with a transmitter (11) and a receiver (12) and an intermediate signal transmission line (3), comprising a first transmission line (31) and a second transmission line (32) for the transmission of differential signals or push-pull signals, characterized in that between the an active filter (1) according to one of the preceding claims for suppressing common mode signals is connected to the first transmission line (31) and the second transmission line (31). Circuit arrangement after Claim 16 , characterized in that the signal transmission line (3) between the transmitter (11) and the receiver (12) is electrically isolated, preferably by an optical coupling, or an inductive coupling, or by a capacitive coupling (7). Circuit arrangement after Claim 16 or 17 , characterized in that the signal transmission line (3) directly connected to the transmitter (11) has a higher voltage level than the signal transmission line (3) directly connected to the receiver (12), and that the active filter (1) is connected to the receiver (12) directly connected signal transmission line (3), or that the transmission line (3) directly connected to the transmitter (11) is at a lower voltage level than the signal transmission line (3) directly connected to the receiver (12) and that active filter (1) is looped into the signal transmission line (3) directly connected to the transmitter (11). Circuit arrangement according to one of the Claims 16 to 18 , characterized in that the circuit arrangement has two pairs of transmitters and receivers which are connected via the signal transmission line (3) in such a way that bidirectional signal transmission takes place in duplex or half-duplex operation, the active filter (1) acting as a bidirectional active filter ( 1) and is looped into the signal transmission line (3) between the first transmission line (31) and the second transmission line (32).

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