U.S. patent application number 14/612977 was filed with the patent office on 2015-12-03 for method and apparatus for wired signal transmission.
The applicant listed for this patent is J. CRAIG OXFORD, D. MICHAEL SHIELDS. Invention is credited to J. CRAIG OXFORD, D. MICHAEL SHIELDS.
Application Number | 20150349843 14/612977 |
Document ID | / |
Family ID | 40454432 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150349843 |
Kind Code |
A1 |
OXFORD; J. CRAIG ; et
al. |
December 3, 2015 |
METHOD AND APPARATUS FOR WIRED SIGNAL TRANSMISSION
Abstract
A method and apparatus for high quality signal transmission,
which utilizes normal-mode current flow and produces an audio
output signal with suppression of normal-mode voltage amplitude,
comprising transmitting an audio input signal source though (1) a
buffer amplifier; (2) a modulated current source; (3) a pair of
wires; (4) a current transformer; and (5) a receiver amplifier for
said current transformer.
Inventors: |
OXFORD; J. CRAIG;
(NASHVILLE, TN) ; SHIELDS; D. MICHAEL; (ST. PAUL,
TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OXFORD; J. CRAIG
SHIELDS; D. MICHAEL |
NASHVILLE
ST. PAUL |
TN |
US
TN |
|
|
Family ID: |
40454432 |
Appl. No.: |
14/612977 |
Filed: |
February 3, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11901702 |
Sep 17, 2007 |
8948273 |
|
|
14612977 |
|
|
|
|
Current U.S.
Class: |
375/258 |
Current CPC
Class: |
H04L 25/0264 20130101;
H04L 25/028 20130101; H04L 25/0266 20130101; H04L 25/0292 20130101;
H04B 3/54 20130101 |
International
Class: |
H04B 3/54 20060101
H04B003/54 |
Claims
1. An apparatus for high quality signal transmission generally in
the sub-audio to video range by means of normal-mode current flow
with suppression of normal-mode voltage amplitude signal comprising
a transmitter and a receiver connected by a pair of wires.
2. The apparatus in claim 1 wherein said transmitter is comprised
of a non-inverting buffer amplifier, an inverting buffer amplifier
and a modulated current source.
3. The apparatus in claim 1 wherein said receiver is comprised of a
current transformer and a receiver amplifier for current
transformer.
4. The apparatus in claim 2 wherein said modulated current source
is single-ended.
5. The apparatus in claim 2 wherein said modulated current source
is symmetrical with respect to the common terminal of said
transmitter.
6. The apparatus in claim 2 wherein said modulated current source
comprises a voltage source and a sufficiently large series
resistance.
7. The apparatus in claim 6 wherein said voltage source is
single-ended.
8. The apparatus in claim 6 wherein said voltage source is
symmetrical with respect to the common terminal of said
transmitter.
9. The apparatus in claim 1 wherein said receiver is comprised of a
current transformer and a receiver amplifier for said current
transformer.
10. The apparatus in claim 9 wherein said receiver amplifier has
essentially zero input impedance.
11. A method of high quality signal transmission, which utilizes
normal-mode current flow and produces an audio output signal with
suppression of normal-mode voltage amplitude, comprising
transmitting an input signal source though (1) a buffer amplifier;
(2) a modulated current source; (3) a pair of wires; (4) a current
transformer; and (5) a receiver amplifier for said current
transformer.
12. The method in claim 11 wherein said modulated current source is
single-ended.
13. The method s in claim 11 wherein said modulated current source
is symmetrical with respect to the transmitter common terminal.
14. The method in claim 12 wherein said modulated current source
comprises a voltage source and a sufficiently large series
resistance.
15. The method in claim 11 wherein said voltage source is
single-ended.
16. The method in claim 11 wherein said voltage source is
symmetrical with respect to the common terminal of the
transmitter.
17. The method in claim 11 wherein said receiver amplifier has
essentially zero input impedance.
Description
[0001] This application is a continuation of U.S. application Ser.
No. 11/901,702, filed Sep. 17, 2007, and is entitled to the benefit
of that filing date in whole or in part. The complete
specification, drawings and disclosure of U.S. application Ser. No.
11/901,702 are incorporated herein by specific reference for all
purposes.
FIELD OF INVENTION
[0002] The present invention is a method of high quality analog or
digital signal transmission by wire, generally in the sub-audio to
video range, by means of normal-mode current flow with suppression
of normal-mode voltage amperage.
BACKGROUND OF INVENTION
[0003] The transmission of audio signals is generally in the range
of 5 Hz-100 kHz between electronic equipment that process or
otherwise employ the signal. Generally, such transmission is done
by originating the signal from a low impedance and receiving it at
a high impedance, often referred to as "voltage matching" or
"bridging". In some (usually large) systems such as telephony the
source and receiving impedances are matched. This is also true in
voltage based video transmission. This is seldom done anywhere else
in contemporary audio practice, either consumer or professional. In
all such systems the signal voltage is impressed across the
dielectric (insulation) of the conductors. As a result, the
properties of the dielectric may strongly affect the quality of the
resulting received signal. Specifically, the attribute of
dielectric absorption seems to impart an audible degradation.
[0004] Industrial control practice has for many years used another
method for transmitting process signals over long distances. It is
known as a current-loop. There are several variations of the
technique, but the most common is known as a 4-20 mA current-loop.
In this method of transmission, the signal is originated from a
high impedance source and received by a low impedance receiver,
essentially the opposite of voltage matching mentioned above.
Generally the bandwidth of 4-20 mA loops is not high enough to
support audio applications, but there is nothing inherent in the
technique which precludes greater bandwidth. Industrial
current-loops generally allow the reporting of a DC value and this
is not necessary for audio or video, which are AC signals. This
permits a different approach to current-based signal
transmission.
SUMMARY OF THE INVENTION
[0005] The present invention is an apparatus for signal
transmission comprising a transmitter and a receiver connected by a
pair of wires. The transmitter is comprised of a non-inverting
buffer amplifier, an inverting buffer amplifier and a pair of
modulated current sources. The receiver is comprised of a current
transformer and a receiver amplifier for the current transformer.
The modulated current source can be single-ended or symmetrical
with respect to the common terminal of the transmitter. The
dielectric properties of the insulation of the pair of wires
connecting the transmitter and receiver do not affect the
transmission quality. The DC resistance of the pair of wires also
does not affect the transmission quality.
[0006] The receiver is comprised of a current transformer and a
receiver amplifier for said current transformer. The receiver
amplifier has essentially zero input impedance.
[0007] The present invention is also a method of high quality
signal transmission, which utilizes normal-mode current flow and
produces an output signal with suppression of normal-mode voltage
amplitude, comprising transmitting input signal source though (1) a
buffer amplifier; (2) a modulated current source; (3) a pair of
wires; (4) a current transformer; and (5) a receiver amplifier for
said current transformer. The modulated current source is
single-ended or is symmetrical with respect to the common terminal
of the transmitter. The modulated current source comprises a
transconductance amplifier or a voltage source, which is
single-ended or is symmetrical with respect to the common terminal
of the transmitter, and a sufficiently large series resistance. The
dielectric properties of the insulation of the pair of wires do not
affect the transmission quality. The DC resistance of the pair of
wires also does not affect the transmission quality. The receiver
amplifier has essentially zero input impedance.
DETAILED DESCRIPTION OF THE INVENTION
[0008] In the following detailed description of the preferred
embodiments, reference is made to the accompanying drawings, which
form a part hereof, and within which are shown by way of
illustration specific embodiments by which the invention may be
practiced. It is to be understood that other embodiments and
structural changes may be made without departing from the scope of
the invention.
[0009] In one embodiment of the present invention, the incoming
signal is fed to a modulated bilateral symmetrical current-source.
A description of a current-source by Thevenin's Theorem is an ideal
generator of current with infinite output impedance. This means
that a specified output current will flow through a connected load
irrespective of the impedance of that load as long as it is finite
or zero. In practice, a current source can be represented as a
source of voltage behind an extremely high resistance. The upper
limit of the voltage is called the compliance voltage; and the
range of approximately constant-current is a function of the ratio
of the range of load impedance to the Thevenin generator
resistance. A modulated bilateral current-source is one, which can
either sink or source current to the load in response to an input
voltage. Such a circuit or device is also known as a Transconducter
and the ratio of output current to input voltage is known as the
transconductance (G). Thus G=Iout/Vin, the unit of G (which stands
for transconductance) in the S.I. system is Siemens.
[0010] A symmetrical current-source is one in which the two
terminals of the current port are identically electrically distant
from the common reference, usually ground. There are numerous
circuit topologies known to those skilled in the art for producing
transconductance amplifiers. Any of several such circuits can be
used to produce the high impedance source required by the
invention. The receiver is another matter. A current-sourced signal
may be accurately received in a summing amplifier at the node which
is commonly known as the virtual ground. Such a circuit may be made
symmetrical as well. The practical difficulty is that exposing
virtual ground to the "outside world" causes stability problems is
real circuit implementations. A far superior method is to regard
the AC current coming from the source as a floating loop and
galvanically sense the current in the loop. This is done by means
of a device known as a current transformer. The advantages of this
method are numerous. For example, the transformer galvanically
isolates the source from the receiver. This eliminates the effects
of common-mode differences in ground potentials between the
equipments. Additionally, the input impedance of the receiver is
essentially a short-circuit. This means that the signal voltage on
the interconnecting cable is essentially zero. This eliminates the
adverse influence of imperfect cable dielectrics because negligible
voltage is impressed across said dielectric. Also, the symmetry of
the transformer primary renders it immune to induced common mode or
longitudinal currents on the interconnecting cable. Finally, the
resistance of the cable has negligible influence on the results
because the equivalent AC impedance of the current-source is
extremely high in comparison to any possible cable resistance.
[0011] A practical current source for the purpose at hand can be
comprised of a differential-output voltage amplifier followed by a
reasonable value of series output resistance. The amplifier must be
able to drive the output resistance as its entire load, since the
receiver will look like a short circuit. If this is done, the same
output configuration can be used in the conventional way, i.e.
bridged by the receiver, thus allowing compatibility with ordinary
receivers in audio applications. In the embodiment shown in FIG. 2,
on the left side (the transmitter) consists of an inverting and a
non-inverting amplifier feeding out to the twisted-pair through
fixed resistors. True modulated current sources can be used, but
their complexity is not necessary to the example. Also, this
topology illustrates the compatibility concept with ordinary
receivers.
[0012] On the right side of FIG. 2, the current transformer is
typically embodied as a toroidal core with the secondary winding
wound toroidally upon it and the primary consisting simply of a
single conductor passing through the center of the toroid. What is
important, however, is the application of the secondary winding
directly to the summing nodes of the two amplifiers. This causes
the secondary voltage across the transformer to be zero by the
feedback action of the amplifiers. The current induced in the
secondary still flows, and the resulting cancellation current in
the feedback resistors of the amplifiers develops an output
voltage. The two voltages are in opposite phase and are differenced
by the third amplifier to produce a single-ended output. The
elimination of secondary voltage on the transformer prevents
magnetic core saturation which would otherwise limit the dynamic
range of operation. The effective shorting of the secondary
magnetizing inductance prevents its reflection to the primary which
extends the time-constant of the transformer thus allowing better
low-frequency response in relation to the core geometry.
[0013] Turning to FIG. 1, in the idealized arrangement the source
of the signal, 1, is passed through a transmitter 9, a pair of
wires of arbitrary length 5, a receiver 10 to produce an output
signal 8. The transmitter 9 is comprised of a non-inverting buffer
amplifier 2, an inverting buffer amplifier 3, and a modulated
current source 4. The receiver 10 is comprised of a current
transformer 6 and a receiver amplifier for the current transformer
7.
[0014] Turning to FIG. 2, in a preferred embodiment the source of
the signal 13, is passed through a transmitter 11, a pair of wires
of arbitrary length 18, a. receiver 12 to produce an output signal
23. The transmitter 11 is comprised of a non-inverting buffer
amplifier 14, an inverting buffer amplifier 15, and Thevenin
current-source resistances 16 and 17. The receiver 12 is comprised
of a current transformer 19, virtual ground amplifiers 20 and 21, a
differential amplifier 22.
BRIEF DESCRIPTION OF FIGURES
[0015] FIG. 1 shows the idealized arrangement.
[0016] FIG. 2 shows a preferred embodiment.
* * * * *