Method and circuit for signal transmission via a current loop

• US 8,885,760 B2
• Filed: 03/23/2010
• Issued: 11/11/2014
• Est. Priority Date: 03/25/2009
• Status: Active Grant

• Current Assignee: Endress + Hauser Conducta Gesellschaft Fur Mess- Und Regeltechnik Mbh + Co. Kg
• Original Assignee: Endress + Hauser Conducta Gesellschaft Fur Mess- Und Regeltechnik Mbh + Co. Kg
• Inventors: Haase, Bjorn, Maringer, Bernd
• Primary Examiner(s): Tran, Khai
• Assistant Examiner(s): Badipour, Bahman
• Application Number:
  US13/258,086
• Publication Number:
  US 20120020430A1
• Time in Patent Office: 1,694 Days
• Field of Search: 375/295
• US Class Current: 375/295
• CPC Class Codes: H03M 3/438 the modulator having a higher order loop filter in the feedforward path
• CPC Class Codes: H03M 3/462 Details relating to the decimation process decimation filters in general H03H17/0416, H03H17/0621
• CPC Class Codes: H03M 7/3028 the quantiser being a single bit one
• CPC Class Codes: H04L 12/40013 Details regarding a bus controller
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26

Abstract

A method for signal transmission between a first and a second system; wherein the first and the second system are connected with one another via a current loop. A direct current signal is transmitted in a first frequency range and an alternating current signal in a second frequency range via the current loop. The direct current signal and the alternating current signal are superimposed and the alternating current signal is used for digital signal transmission and the direct current signal is used for analog signal transmission. By means of a control unit, a first data stream is produced, in which the direct current signal and alternating current signal to be set in the current loop are digitally encrypted. The first data stream is transmitted to an electrical current output circuit and the transmitted first data stream is converted by the electrical current output circuit into an electrical current signal. The electrical current signal is composed of the superimposed direct current signal and alternating current signal, or the transmitted first data stream is converted by the electrical current output circuit into the direct current signal and the alternating current signal. The electrical current signal or the direct current signal and the alternating current signal are set in the current loop.

Claims

1. A method for signal transmission between a first and a second system, wherein the first and the second system connected with one another via a current loop, a direct current signal is transmitted in a first frequency range from 0-30 Hz and an alternating current signal is transmitted in a second frequency range from 100-10000 Hz via the current loop, the direct current signal and the alternating current signal are superimposed, wherein the direct current signal and alternating current to be set in the current loop are encrypted in a digital manner, the alternating current signal is used for digital signal transmission and the direct current signal is used for analog signal transmission, comprising the steps of:

producing by means of a control unit, said first data stream, in which the direct current signal and the alternating current signal to be set in the current loop are digitally encrypted;

transmitting the first data stream to an electrical current output circuit; and

converting the transmitted first data stream by the electrical current output circuit into an electrical current signal, wherein;

the electrical current signal is composed of the superimposed direct current signal and alternating current signal, or that the transmitted first data stream is converted by the electrical current output circuit into the direct current signal and the alternating current signal; and

the electrical current signal or the direct current signal and the alternating current signal are set in the current loop.

2. The method for signal transmission as claimed in claim 1, wherein:

at least a first control signal, in which the alternating current signal and direct current signal to be set in the current loop are digitally encrypted, is produced by the control unit, and at least a second control signal is produced by the control unit, in which the direct current signal to be set in the current loop is digitally encrypted.

3. The method for signal transmission as claimed in claim 2, wherein:

by means of the first control signal, at least one numerical value is produced, which corresponds to the alternating current signal to be set.

4. The method for signal transmission as claimed in claim 2, wherein:

by means of the first control signal, a sequence of numerical values is produced, wherein the sequence corresponds to the alternating current signal to be set.

5. The method for signal transmission as claimed in claim 3, wherein:

the numerical value or individual numerical values of the sequence are produced in a format with a bit width of n bits, wherein n is a natural number, especially three or four.

6. The method for signal transmission as claimed in claim 2, wherein:

by means of the second control signal, a numerical value corresponding to the direct current signal to be set, especially with a bit width of less than m bits, is produced, wherein m is a natural number.

7. The method for signal transmission as claimed in claim 6, wherein:

at least one numerical value of the sequence, which represents the alternating current signal, is scaled, especially to the bit width of the numerical value of the DC signal.

8. The method for signal transmission as claimed in claim 6, wherein:

at least one numerical value of the sequence representing the alternating current signal, and the numerical value of the DC signal to be set, are combined, especially added, and are converted into the first data stream.

9. The method for signal transmission as claimed in claim 8, wherein:

said conversion is performed by means of a digital delta-sigma modulator, wherein;

the digital delta-sigma modulator is operated in first or second order dependent on an input value, the input value being dependent on the direct current signal and/or alternating current signal to be set; and

the input value is derived especially from at least one numerical value of the sequence, which corresponds to the alternating current signal to be set and/or to the numerical value of the DC signal to be set.

10. The method for signal transmission as claimed in claim 1, wherein:

the direct current signal and the alternating current signal set in the current loop are converted into a second data stream;

the direct current signal and the alternating current signal are digitally encrypted in the second data stream, and

the second data stream is transmitted back from the electrical current output circuit to the control unit.

11. The method for signal transmission as claimed in claim 1, wherein:

the superimposed direct current and alternating current signal set in the current loop is sampled and converted into a second data stream.

12. The method for signal transmission as claimed in claim 11, wherein:

the sampling rate of the second data stream is lessened, especially by means of a decimation filter.

13. The method for signal transmission as claimed in claim 12, wherein:

from the especially decimated second data stream, especially a decimated second data stream, a first numerical value is ascertained, which represents the direct current and alternating current signal set in the current loop.

14. The method for signal transmission as claimed in claim 13, wherein:

from the first numerical value, a second numerical value is derived, which corresponds to the direct current signal set in the current loop, and from the first numerical value, a third numerical value is derived, which corresponds to the alternating current signal set in the current loop.

15. The method for signal transmission as claimed in claim 14, wherein:

a frequency response correction of the sampled especially decimated direct current and/or alternating current signal, especially a decimated signal, is performed.

16. The method for signal transmission as claimed in claim 15, wherein:

the third numerical value is converted or decoded, especially by means of a quadrature demodulator, into signals readable by the control unit and transmitted to the control unit.

17. The method for signal transmission as claimed in claim 1, wherein:

the first data stream and/or the second data stream are transmitted across a galvanic barrier.

18. The method for signal transmission as claimed in claim 1, wherein:

a value of the DC signal and/or AC signal set in the current loop and transmitted back is compared with a desired value by means of the control unit.

19. The method for signal transmission as claimed in claim 1, wherein:

an operating mode is provided, in which operating mode a maximum value of the DC signal settable in the current loop is predetermined by means of the first data stream, in which operating mode the value of the DC signal in the current loop is furthermore limited by a unit provided in the second system to a value smaller than or equal to predetermined the maximal value, and in which operating mode the value of the DC signal set in the current loop is transmitted via the second data stream to the control unit.

20. The method for signal transmission as claimed in claim 1, wherein:

the alternating current signal set in the current loop is an essentially sinusoidal, alternating current signal; and

overtones of the sinusoidal AC signal up to and including 6th order are attenuated by a value of at least 30 dB relative to the amplitude of the fundamental oscillation of the sinusoidal AC signal.

21. The method for signal transmission as claimed in claim 20, wherein:

at least one overtone of 7th order or a higher order is attenuated by a value of less than 30 dB relative to the amplitude of the fundamental oscillation.

22. An electrical and/or electronic circuit for signal transmission between a first and a second system, said first and said second system are connected with one another via a current loop, wherein the current loop serves to transmit a direct current signal in a first frequency range from 0-30 Hz and an alternating current signal in a second frequency range from 100-10000 Hz, wherein the alternating current signal and the direct current signal are superimposed, wherein the direct current signal and alternating current to be set in the current loop are encrypted in a digital manner, and wherein the direct current signal serves for analog signal transmission and the alternating current signal serves for digital signal transmission, comprising:

a control unit, which serves for producing said first data stream, which the direct current signal and alternating current signal to be set in the current loop are digitally encrypted;

an electrical current output circuit in said second system; and

a first transmission unit, which serves to transmit said first data stream to said electrical current output circuit, wherein;

said electrical current output circuit serves to convert said transmitted first data stream into an electrical current signal; and

said electrical current signal is composed of the superimposed direct current signal and alternating current signal, or the electrical current output circuit serves to convert the transmitted first data stream into the direct current signal and the alternating current signal.

23. The electrical and/or electronic circuit as claimed in claim 22 further comprising:

a digital switching unit, which serves for producing said first data stream, especially the AC signal to be set in said current loop, by means of a first control signal-especially a digital control signal-output by said control unit.

24. The electrical and/or electronic circuit as claimed in claim 23, wherein:

said control unit has a digital communication interface, especially a serial digital communication interface, and the digital communication interface serves for transmission between said digital switching unit and said control unit of control signals representing the alternating current signal to be set.

25. The electrical and/or electronic circuit as claimed in claim 24, wherein:

said digital switching unit serves to produce from the control signals transmitted by said control unit via the digital communication interface at least one numerical value or a sequence of numerical values;

the numerical value or the sequence corresponds to the alternating current signal to be set in said current loop; and

the numerical values are especially presented in a format with a bit width of n bits.

26. The electrical and/or electronic circuit as claimed in claim 25, further comprising:

a register, which is operable from said control unit, especially by means of a second control signal, and serves to output a numerical value corresponding to the direct current signal to be set, wherein;

the numerical value is presented in a format with a bit width of m bits.

27. The electrical and/or electronic circuit as claimed in claim 22, further comprising:

a first signal processing unit, which includes a digital sigma-delta modulator, which serves to produce said first data stream, especially from the numerical value that represents the direct current signal and the alternating current signal.

28. The electrical and/or electronic circuit as claimed in claim 27, wherein:

said sigma-delta modulator is embodied in such a manner, that said sigma-delta modulator is operable in a first or second order as a function of an input value derivable from the alternating current signal and direct current signal to be set in said current loop.

29. The electrical and/or electronic circuit as claimed in claim 22, further comprising:

a synchronizing unit, which serves to synchronize the transmitted first data stream with a predetermined clock signal.

30. The electrical and/or electronic circuit as claimed in claim 22, wherein:

said electrical current output circuit has a first filter with a low-pass characteristic curve, which converts the transmitted first data stream into an analog voltage.

31. The electrical and/or electronic circuit as claimed in claim 22, wherein:

the electrical and/or electronic components of the electrical current output circuit are spatially surrounded by electrically conductive traces; and

the conductive traces are actively held to essentially the same DC potential as the electrical and/or electronic components.

32. The electrical and/or electronic circuit as claimed in claim 22, wherein:

said current output circuit has a second signal processing unit, which converts the direct current signal and/or alternating current signal set in said current loop into a second data stream; and

the direct current signal and the alternating current signal are digitally encrypted in said second data stream.

33. The electrical and/or electronic circuit as claimed in claim 32, wherein:

said second signal processing unit has an analog delta-sigma modulator, which serves to produce said second data stream.

34. The electrical and/or electronic circuit as claimed in claim 33, wherein:

a loop filter of said analog delta-sigma modulator used for modulation is a time-continuous filter.

35. The electrical and/or electronic circuit as claimed in claim 22, further comprising:

a second transmission unit, which serves to transmit said second data stream to said control unit.

36. The electrical and/or electronic circuit as claimed in claim 22, further comprising:

a decimation filter, especially a CIC filter, which serves to change the sampling rate of said second data stream.

37. The electrical and/or electronic circuit as claimed in claim 36 wherein:

said decimation filter outputs a numerical value or a sequence of numerical values, which represents the direct current signal and the alternating current signal set in said current loop.

38. The electrical and/or electronic circuit as claimed in claim 22, further comprising:

a filter, especially a moving average filter, which separates from one another a first part of the numerical value and a second part of the numerical value which represent the direct current signal and the alternating current signal set in the current loop, wherein;

said first part corresponds to the alternating current signal set in said current loop, and the second part corresponds to the direct current signal set in said current loop.

39. The electrical and/or electronic circuit as claimed in claim 26, wherein:

said register additionally serves to process the second part of the numerical value.

40. The electrical and/or electronic circuit as claimed in claim 38, wherein:

said first part is fed to a quadrature demodulator, which produces signals readable by said control unit, especially an RxD signal and a carrier detect signal.

41. The electrical and/or electronic circuit as claimed in claim 40, wherein:

said RxD signal and the carrier detect signal are deliverable via the digital communication interface UART of said control unit.

42. The electrical and/or electronic circuit as claimed in claim 22, wherein:

the alternating current signal set in said current loop is an essentially sinusoidal, alternating current signal; and

overtones of the sinusoidal AC signal up to and including 6th order are attenuated by a value of at least 30 dB relative to the amplitude of the fundamental oscillation of the sinusoidal AC signal.

43. The electrical and/or electronic circuit as claimed in claim 42, wherein:

at least one overtone of 7th order or a higher order is attenuated by a value of less than 30 dB relative to the amplitude of the fundamental oscillation.

44. The electrical and/or electronic circuit as claimed in claim 22, wherein:

the first system comprises only digital components.

45. The electrical and/or electronic circuit as claimed in claim 22, wherein:

said first data stream is a bit stream.

46. A field device of process and/or automation technology having an electrical and/or electronic circuit, comprising:

a control unit, which serves for producing a first data stream, which the direct current signal in a first frequency range from 0-30 Hz and alternating current signal in a second frequency range from 100-10000 Hz to be set in the current loop are digitally encrypted;

an electrical current output circuit; and

a first transmission unit, which serves to transmit said first data stream to said electrical current output circuit, wherein;

said electrical current output circuit serves to convert said transmitted first data stream into an electrical current signal; and

said electrical current signal is composed of the superimposed direct current signal and alternating current signal, or the electrical current output circuit serves to convert the transmitted first data stream into the direct current signal and the alternating current signal.

47. The field device of process and/or automation technology as claimed in claim 46, wherein:

said field device is an actuator or a measuring transducer/sensor.

48. The field device of process and/or automation technology as claimed in claim 46, wherein:

said first data stream is a bit stream.