RU2714224C1 - Data transmission device with galvanic isolation by means of pulse transformer - Google Patents

Abstract

FIELD: data transmission means.

SUBSTANCE: disclosed is a data transmission device with galvanic isolation using a pulse transformer, comprising an input Schmitt trigger with a paraphrase output, four univibrators, two buffer amplifiers with output to the transformer, at the output of the transformer there is a differential amplifier, two comparators, an RS-trigger and an output buffer amplifier.

EFFECT: high noise-immunity, unambiguous recovery of the shape of the original signal, reduced intersymbol interference.

4 cl, 6 dwg

Description

The present invention relates to the field of electronics and digital data transmission devices. It is intended for use as a data transmission device with galvanic isolation by means of a pulse transformer with a data transfer rate of at least 20 Mbit / s.

It is known that for the transmission of galvanically isolated data, various physical principles of signal transmission through an insulating non-conductive medium can be used. These principles include:

1. Signal transmission through a static magnetic field.

In this case, a pair is used: the source of the magnetic field is an open electromagnetic coil and a magnetically sensitive element, for example, a magnetically sensitive resistor or a Hall sensor. An example of such devices is the IL600 series of NVE Corporation chips manufactured with IsoLoop® technology and protected by US Pat. No. 5,831,426; and No. US 6,300,617.

The disadvantages of this principle of signal transmission include the following:

- sensitivity to external permanent magnetic fields,

- the technological complexity of the manufacturing process of magnetically sensitive elements in the framework of typical silicon CMOS technologies.

2. Signal transmission through an electrostatic field.

In this case, a high voltage capacitor is used as an element of high voltage isolation. An example of such devices is the Texas Instruments Incorporated ISO723X series of chips.

The disadvantages of this principle of signal transmission include the following:

- the complexity of signal formation: the method of frequency separation of the transmitted signal and its “assembly” on the secondary side are used.

- The required breakdown voltage is achieved by an additional, not typical, technological operation of the CMOS process.

3. Transmission of signals through an electromagnetic field (micropower radio signal). An isolation capacitor is also used. An example of such devices is the Si84xx series of chips from Silicon Laboratories Inc (US No. 7,738,568).

The disadvantages of this principle of signal transmission include the following:

- The same disadvantages as in the previous version, plus increased power consumption.

Closest to the invention is a data transmission device with galvanic isolation using a pulse transformer, which is based on the isolation technology of Analog Devices, called iCoupler. [US patent No. 7683654]. This device is selected as a prototype of the proposed solution.

In the patent formula, 11 paragraphs are described that describe various methods for distinguishing the leading and trailing edges of an input transmitted logical signal and methods for its restoration on the secondary side. The main idea of the invention lies in various methods of converting the edges of the input signal into various unipolar pulses, which differ from each other either in quantity or in duration.

In more detail in Russian literature, the principle of operation of the iCoupler system is described in the article [1].

The disadvantages of this technical solution include the following:

- the need to limit the minimum pulse width of the input signal to uniquely select the transmission of the leading or trailing edges;

- with the indicated method of generating pulses, a constant component occurs in the transformer, which leads to the occurrence of intersymbol interference of the output signal.

The technical result achieved by using the proposed device is to expand the functionality of the device:

- in increasing noise immunity;

- the unambiguity of the restoration of the shape of the original signal;

- in reducing intersymbol interference.

This is achieved due to the fact that in a data transmission device with galvanic isolation, with galvanic isolation by means of a pulse transformer, containing a Schmitt input trigger with a paraphase output to the non-inverting output of which is connected the first one-shot to the output of which the third one-shot is connected, and to the inverting output of the input trigger the second one-shot is connected; the outputs of the first and fourth one-shots are connected to the first logical element OR, the outputs of the second and third are one ibratorov attached to the second OR gate, the outputs of OR gates are respectively connected to the inputs of buffer amplifiers whose outputs are in turn connected to inputs of the transformer primary winding.

In turn, the outputs of the pulse transformer are connected to a differential correction amplifier containing proportionally integrating RC links, the differential output of the amplifier is connected to the inputs of two comparators, the first of which is triggered by an input signal of positive polarity, and the second is triggered by a signal of negative polarity, the outputs of the comparators are connected to the inputs of the RS-trigger, which restores the shape of the input signal, an output buffer amplifier is connected to the output of the RS-trigger troystva.

There is an option in which the reset input of the first multivibrator is connected to the output of the first comparator, the output of which is connected to the second alternative reset input of the RS flip-flop.

A variant is possible where the OR gate is connected to the outputs of the first and second single-vibrators, the output of which is connected to the reset input of the second multivibrator, the output of which is connected to the first alternative inputs of the first and second logical elements “AND”, the non-inverting and inverting are connected to the second inputs respectively the outputs of the Schmit trigger, while the output of the first logic element “AND” is connected to the second alternative input of the first one-shot, and the output of the second logic element And It attaches to the second input of the second monostable alternative.

A variant is also possible in which resistors are connected to the outputs of a planar transformer, a common point of which is connected to the output of the operational amplifier, a non-inverting input of which is connected to a power source with an output voltage equal to half the supply voltage of the differential amplifier, and a common point of resistors is connected to the inverting input, the second the ends of which are connected to the inputs of a differential amplifier.

In fig. 1 is a diagram of the inventive data transmission device with galvanic isolation using a planar transformer, where:

100 - Smith input trigger; 101, 102, 103, 104 - single vibrators; 105, 106 - logical elements OR; 107, 108 — buffer amplifiers; 109 - pulse transformer; 114 - differential amplifier; 110, 111, 113, 115 - resistors of the frequency correction circuits; 112, 116 - frequency correction capacitors; 117, 118 - comparators with an asymmetric threshold; 119, - RS-trigger; 120 - output buffer amplifier.

In fig. 2 shows a variant of the device, which differs from the variant in Fig. 1 in that the output of the first comparator 117 is connected to the reset input of the first multivibrator 400, the output of which is connected to the second alternative reset input of the RS trigger 119.

In fig. 3 is a diagram of a device in which, compared with the variant of Fig. 1, the OR gate 302 is connected to the outputs of the single-shots 101 and 102, the output of which is connected to the reset input of the second multivibrator 303, the output of which is connected to the first alternative inputs of the first and second logic gates “AND "300 and 301, to the second inputs of which respectively are connected the non-inverting and inverting outputs of the Schmit trigger 100, while the output of the first logical element And 300 is connected to the second alternative input of the first one-shot Ator 101, and the output of the second AND gate 301 is connected to a second input of the second alternative monostable 102

In fig. Figure 4 shows a circuit that differs from the variant in Fig. 1 in that resistors 500 and 501 are added to the outputs 200 and 201 of the pulse transformer 109, the common point of which is connected to the output of the operational amplifier 502, to the non-inverting input of which a power source is connected, with an output voltage equal to half voltage supply of the differential amplifier, and a common point of resistors 503 and 504 is connected to the inverting input, the second ends of which are connected to the inputs of the differential amplifier 114.

A data transmission device with galvanic isolation by means of a pulse transformer (Fig. 1), containing an Schmitt input trigger with a paraphase output, to the non-inverting output of which a first one-shot is connected, to the output of which a third one-shot is connected, and to the inverting output of a Schmitt input, a second one-shot and second one-shot outputs single vibrators are connected to the first logical element "OR", the outputs of the second and third single vibrators are connected to the second logical element that OR, the outputs of the logical elements "OR" are respectively connected to the inputs of the buffer amplifiers, the outputs of which are in turn connected to the inputs of the primary winding of a planar transformer,

in turn, the outputs of the planar transformer are connected to the input differential correction amplifier containing proportionally integrating RC links, the differential output of the amplifier is connected to the inputs of two comparators, the first of which is triggered by an input signal of positive polarity, and the second is triggered by a signal of negative polarity, the outputs of the comparators are connected to the inputs of the RS-trigger, which restores the shape of the input signal, the output buffer ilitel data transmission device with galvanic isolation via the planar transformer.

There is an option (Fig. 2) in which the reset input of the first multivibrator is connected to the output of the first comparator, the output of which is connected to the second alternative reset input of the RS-flip-flop.

There is an option (Fig. 3) in which the OR gate is connected to the outputs of the first and second single-vibrators, the output of which is connected to the reset input of the second multivibrator, the output of which is connected to the first alternative inputs of the first and second logical elements “AND”, to the second inputs which respectively connect the non-inverting and inverting outputs of the Schmit trigger, while the output of the first logical element “And” is connected to the second alternative input of the first one-shot, and the output of the second th element "I" is coupled to the second input of the second monostable alternative.

A variant is also possible (Fig. 4), in which resistors are connected to the outputs of the pulse transformer, the common point of which is connected to the output of the operational amplifier, to the non-inverting input of which a power source is connected, with the output voltage equal to half the supply voltage of the differential amplifier, and connected to the inverting input a common point of resistors whose second ends are connected to the inputs of a differential amplifier.

The device operates as follows:

An input digital signal with edges of arbitrary duration, up to 2-3 μs, is fed to the input of a Schmit trigger (100) with a paraphase output, where it is converted into a paraphase signal with steep edges. Further, this signal is fed to the inputs of single vibrators 101 and 102, which respectively act on the edge (101) or fall (102) of the input signal and produce single, so-called “information” pulses of about 2-3 ns duration, these pulses, in turn, trigger single vibrator 103 or 104, respectively. Single vibrators 103 and 104 form single, so-called “demagnetizing” pulses. "Demagnetizing" pulses are necessary to return the current of the transformer to its original, "zero" state, and thereby eliminates intersymbol interference. Next, the output signals are fed to the OR logic elements (105, 106) and to the buffer amplifiers 107 and 108. From the outputs of the buffer amplifiers, the signals are fed to the primary winding of the planar transformer 109. Then, from the output of the transformer, the signal is fed to the correction amplifier 114, the frequency correction is carried out elements 110, 111, 112, 113, 115 and 116. Frequency correction is necessary to compensate for distortions arising in the pulse transformer. The reconstructed signal is fed to the inputs of the comparators 117 and 118, which transform, due to the offset threshold of operation, the bipolar transformer signals into short pulses of positive polarity. Next, using the RS-trigger 119 restores the original input signal, which is fed to the output buffer amplifier 120.

Timing diagrams explaining the operation of the device are shown in Fig. 5a and 5b. In fig. 5a, the upper graph shows the input voltage, the next graph shows the output signals of single vibrators, following each other the first pulse will be called “information”, and the second “demagnetizing”. The following graph shows the differential voltage across the transformer primary. The graph shows that the first pulse in amplitude is less than the second, this is due to the fact that at the first pulse the current is opposite to the voltage (counter-EMF) and in the second pulse the voltage and current coincide in the direction the voltage drop from the flowing current is added to the EMF of the transformer winding. The last graph shows the current of the primary winding of the transformer. It can also be seen from the graph that the current due to the small value of the inductance of the pulse transformer first rises, and when a “demagnetizing” pulse is applied, it decreases at a speed determined by the supply voltage of the output buffer amplifiers.

EMF winding approximately corresponds to:

When applying the "informational" impulse E _TV = V _cc -I _m * (R _buf + R _TV ),

When applying a "demagnetizing" pulse E _TV = V _cc + I _m * (R _buf + R _TV ),

Where E _TV is the winding EMF, V _cc is the supply voltage of the buffer amplifiers, I _m is the transformer winding current, R _buf is the output resistance of the buffer amplifiers, R _TV is the transformer winding resistance, the slew rate of the transformer winding is determined by the formula dI _m / dt = E _TV / L _TV , where L _TV is the transformer winding inductance.

It can be seen from the above formulas that, in practice, by a parametric (indirect) method, by adjusting the magnitude of the “demagnetizing” depending on the resistances, it is possible to achieve a small residual value of the transformer winding current, thereby ensuring that the shape of subsequent pulses is independent of previous ones at a high repetition rate of input signals . Those. ensure minimal intersymbol interference and increase noise immunity at a high repetition rate of input pulses.

In fig. 5b, the input and output signals of the device are shown in the upper graph, the differential voltage at the output of the planar transformer is shown in the following graph, the output voltage of the correction amplifier is shown, and the output voltage of the comparators is shown in the last graph. The graphs show that when the input pulse duration is 12 ns, intersymbol interference is completely absent. The production of experimental samples showed that when implementing a chip using 0.25 μm technology, the maximum data transfer frequency without distortion can reach 200 Mbit / s.

In cases where there is a need to remove the uncertainty of the output signal in case of power failure at the input part of the device (up to a pulse transformer) or “freezing” of the input signal source, the device can be supplemented, as shown in Fig. 2. In the circuit of the output part of the device at the output of the comparator 117 (a comparator for receiving a logical “1” signal, a multivibrator is installed at the input, which is reset by the signal of this comparator and performs the function of a time delay. And if an input reset signal is not received within a specified time delay, then the first output signal of the multivibrator resets the output signal of the device to the state log "0", thereby removing the uncertainty in the input signal.

In cases where the input signal changes its state quite rarely, and at the output of the device it is desirable to have information about the input status (activity) not less than, for example, 1 ms, then a multivibrator 303 can be introduced into the input circuit of the device, periodically confirming with pulses in the transformer , the state of the input signal, as shown in Fig. 3. To do this, the “OR" element 302 is installed at the output of the comparators 101 and 102, which, if there is activity in the input signal, constantly resets the multivibrator 303. If the state of the input signal does not change during the time specified by the multivibrator, then the output signal of the multivibrator is periodically through matching schemes “I” 300 or 301 confirms the current state of the input and confirmation pulses are generated in the transformer, transmitted to the output of the device.

In cases where it is necessary to ensure the operation of the device at high speeds of changing the isolation voltage and suppressing the common mode current flowing through the transformer through passage and entering the input of a differential amplifier with a level that threatens to saturate the input stages, a compensating operational amplifier can be introduced into the transformer signal receiving circuits, holding input common-mode voltage at a given level. The maximum rate of rise of the insulation voltage at which the common-mode parasitic current can be suppressed is determined by the formula:

dU / dt = ± V _amp / (C _TV * R _comp ), where dU / dt = is the rate of change of the insulation voltage, ± V _amp is the amplitude of the output voltage of the compensating amplifier, C _TV is the passage capacity of the transformer. R _comp is the value of the compensating resistors.

At ± V _amp = 1.5 V, C _TV = 2 pF, R _comp = 30 Ohm dU / dt = 25 kV / μs,

which is a good indicator for devices of this type.

The use of two buffer amplifiers with a paraphase output to the transformer winding made it possible to supply to the transformer a sequence of two consecutive bipolar pulses arising in a data transmission device with galvanic isolation by means of a planar transformer containing Schmitt input trigger with a paraphase output to the non-inverting output of which the first is connected a single-shot to the output of which a third one-shot is connected, and to the inverting output of the input Schmitt trigger, the second one-shot is connected, the outputs of the first and fourth one-shots are connected to the first OR gate, the outputs of the second and third one-shots are connected to the second OR gate, the outputs of the OR gates are respectively connected to the inputs of the buffer amplifiers, the outputs of which are in turn connected to the inputs of the primary winding of a planar transformer, which led to the suppression of intersymbol interference, an increase in the signal transmission rate and an increase in the noise immunity of the device ystvo in general.

The execution of the first multivibrator in the output part of the device, the reset input connected to the output of the first comparator connected, the output to the second alternative RS reset input of the trigger, allowed to remove the uncertainty in the output signal in case of power failure of the input part and in other unauthorized cases.

Connection to the outputs of the first and second single-vibrators of the OR logic element, the output of which is connected to the reset input of the second multivibrator, the output of which is connected to the first alternative inputs of the first and second logic elements AND, the second inputs of which are respectively connected to the non-inverting and inverting outputs of the Schmit trigger , while the output of the first logic element “And” is connected to the second alternative input of the first one-shot, and the output of the second logic element “And” is connected to the second alternative input of the second one-shot, provides confirmation of the logical state of the input signal by retransmitting a pair of bipolar pulses with a period of operation of the multivibrator.

Connecting to the outputs of a planar transformer two resistors, the common point of which is connected to the output of the operational amplifier, to the non-inverting input of which a power source is connected, with an output voltage equal to half the supply voltage of the differential amplifier, and a common point of resistors is connected to the inverting input, the second ends of which are connected to the inputs differential amplifier, provides compensation for stray currents flowing through the passage capacity of the transformer with sharp drops x tension between the two sides of galvanic isolation.

Sources of information

1. Isolation ICs based on iCoupler technology from Analog Devices. Dmitry Ioffe. Components and Technologies No. 7 of 2006

2. Si84XX Digital Isolators from Silicon Laboratories. Yaroslav Komolov. Components and Technologies №2 2007

3. Advantages of using a double capacitive barrier in new Texas Instruments digital isolators. Sergey Pichugin. Components and Technologies №14 2008

4. “Chips of embedded wired modems ISOmodem manufactured by SiLabs” Alexey Kurilin. "Electronic Components" No. 5, 2006

5. “Digital devices / Generators / single vibrators” digital.sibsutis.ru/

6. “Inside Coupler® Technology: ADuM347x PWM Controller and Transformer Driver with Quad-Channel Isolators” Design Summary. By Flow Zhao, Design Engineer. 2010 Analog Devices, Inc.

7. "HCPL-9000 / -0900 / -9030 / -0930 / 9021/0931 / -900J / -090J / -901J / -091J / -902J / -092J" Data Sheet. Agilent Technologies 2002.

8. “ISOLATED RS-485 PROFIBUS TRANSCEIVER” Data Sheet. 2008, Texas Instruments Incorporated

9. “HIGH SPEED, TRIPLE DIGITAL ISOLATORS)) Data Sheet. 2008, Texas Instruments Incorporated

10. "Si8410 / 20/21" Data Sheet. 2011 Silicon Laboratories

11. “High-Voltage Lifetime of the ISO72x Family of Digital Isolators)) Application Report 2006, Texas Instruments Incorporated

12. US patent 5,952,849. Sep. 1999.

13. US patent 6,873,065. Mar. 2005.

14. US patent 6,903,578. Jun. 2005.

15. US patent 7,683,654. Mar. 2010.

16. US patent 7,738,568. Jun. 2010.

Claims (4)

1. A data transmission device with galvanic isolation, containing a pulse transformer, at the input of which there is a transmitting device that modulates the input signal, and at the output, a device that demodulates the input signal, characterized in that the input contains an Schmitt input trigger with a paraphase output, to a non-inverting output which the first one-shot is connected to, the output of which is the third one-shot, and the second one-shot is connected to the inverting output of the Schmit input trigger, the outputs of the first and even grated single-vibrators are connected to the first logical element "OR", the outputs of the second and third single-vibrators are connected to the second logical element OR, the outputs of the logic elements "OR" are respectively connected to the inputs of the buffer amplifiers, the outputs of which are in turn connected to the inputs of the primary winding of the pulse transformer, in turn, the outputs of the pulse transformer are connected to the input differential correction amplifier containing proportionally integrating RC links, differential The main output of the amplifier is connected to the inputs of two comparators, the first of which is triggered by an input signal of positive polarity, and the second is triggered by a signal of negative polarity, the outputs of the comparators are connected to the inputs of the RS trigger, which restores the shape of the input signal, and the output buffer is connected to the output of the RS trigger amplifier of a data transmission device with galvanic isolation from a pulse transformer. 2. The data transmission device with galvanic isolation using a pulse transformer according to claim 1, characterized in that the output of the first comparator is connected to the reset input of the first multivibrator, the output of which is connected to the second alternative reset input of the RS trigger 3. The data transmission device with galvanic isolation using a pulse transformer according to claim 1, characterized in that the logic element "OR" is connected to the outputs of the first and second single-vibrators, the output of which is connected to the reset input of the second multivibrator, the output of which is connected to the first alternative inputs the first and second logical elements "AND", to the second inputs of which respectively are connected the non-inverting and inverting outputs of the Schmit trigger, while the output of the first logical element "And" is connected ene entry to the second alternative of the first monostable multivibrator and the output of the second AND gate "AND" the second alternative is attached to the input of the second monostable multivibrator. 4. The data transmission device with galvanic isolation using a pulse transformer according to claim 1, characterized in that resistors are connected to the outputs of the planar transformer, the common point of which is connected to the output of the operational amplifier, to the non-inverting input of which a power source with an output voltage equal to half is connected voltage supply of the differential amplifier, and a common point of resistors is connected to the inverting input, the second ends of which are connected to the inputs of the differential amplifier.

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