Abstract:
This invention relates to data communication equipment (DCE), more specifically, high speed transmission of electronic data between data terminal equipment (DTE). The invention sets forth a method and a device for transmitting a voltage signal waveform as a series of current pulses onto a communication line. The method requires converting an input voltage signal waveform to a current signal waveform and transmitting the resulting current pulses onto a communication line wherein a predetermined bias voltage is maintained.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/111,170, filed Dec. 7, 1998. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to a method and device for transmitting data over a transmission medium at high speeds. More specifically, the present invention relates to using variations in electrical current for representing and conveying data over a transmission medium. 
     BACKGROUND OF THE INVENTION 
     There are many modems on the market today for high speed data bit transmission on a twisted-pair of copper telephone lines. Constant demand for increased amounts of data bit transmission has generated the continual need for faster modems capable of transmitting and receiving greater amounts of data. While many high speed transmission techniques such as ADSL and HDSL have emerged in response to this technological demand, there continues to remain a demand for yet greater data transmission rates. In addition, it would be extremely advantageous if the technology incorporating the higher transmission rates were able to implement existing electrical communication infrastructure, i.e., twisted-pair telephone lines. An additional preference would allow for the transmission of these signals at lower power over greater distances without needing fewer or any repeaters to amplify the signal. 
     Conventionally, data transmission is sent via voltage signals that are susceptible to many factors that may adversely affect the quality and distance of the transmission. Some of these factors include: random distortion noise, inherent characteristics or poor physical condition of the transmission line, transmission line length, high frequency, attenuation and distortion effects. One common approach used to overcome some of these adverse affects is to increase the transmission power. Of course, the greater the distance, the greater the impedance and the likelihood of effects due to exposure to external noise sources. FCC regulations also limit frequency levels and power levels of transmission. Bridge taps and loading coils, present in phone line infrastructure also present significant impediments to voltage signal data transmission. Bridge taps tend to divide voltage signals hence weakening them. Loading coils tend to resist changes in voltage level hence degrading data characterized by voltage level. 
     The amount of data that can be transmitted is directly related to the number of quantization levels that a transmitter utilizes. Random distortion noise directly affects the amount of quantization levels. Attempting to increase a transmission rate by merely increasing the amount of quantization levels beyond that in which the data bits can be determined is not useful. To date, the limitations on quantization caused by random distortion noise has prevented conventional modems and transmission techniques from meeting the demand for higher data transmission speed. 
     Additionally, today&#39;s transmission lines incorporate repeaters that amplify a signal that has attenuated or weakened during its transmission. The repeater is necessary to re-amplify the affected signal. A transmission signal that is expected to travel a great distance must often be re-amplified repeatedly. 
     Hence, prior to the present invention, a need existed for a method of data transmission capable of better recognizing and discriminating a signal from accompanying noise. Also needed, were methods and apparatus for transmitting data signals which would avoid or significantly reduce the adverse effects of the factors cited above, so as to provide data transmissions of higher quality, increased capacity, and longer transmission distances at lower power with fewer, or no need for repeaters. 
     SUMMARY OF THE INVENTION 
     This invention relates to data communication equipment (DCE), more specifically, a modem capable of high speed transmission of electronic data between data terminal equipment (DTE). Broadly stated, this invention sets forth a method and a device for transmitting data as a series of current pulses onto a transmission medium such as a communication line. The method requires converting an input signal waveform to a current signal waveform and transmitting the resulting current pulses onto a communication line wherein a predetermined bias voltage is maintained. 
     Transmitting data as current pulses is an improved method of transmitting data, as opposed to using voltage pulses, because current is not affected as much by capacitance. By virtue of Kirchoffs&#39; Law, this allows the transmission of data over greater distances because the signal is less attenuated by line capacitance. With an increase in shunt capacitance and/or an increase in frequency across the capacitance, voltage data pulses weaken. Therefore, bridge taps associated with the current phone line infrastructure will not degrade the signals transmitted according to the invention to the same degree as they degrade (divide) conventional voltage signal waveforms. It is also known that loading coils exist in the infrastructure, are resistant to voltage changes, hence, the loading coils present a significant impediment to voltage waveform signals. On the other hand, it is believed that signals transmitted according to the present invention should be far less affected by loading coils. 
     Another embodiment of this invention includes a method of generating representative pulses of current from an input (either current or voltage) waveform and transmitting resulting current pulses onto a communication line. Another aspect of the invention includes receiving the current pulses, measuring the current pulses, and translating the measured current pulses into data. 
     A circuit for carrying out the method as it relates to transmitting standard voltage-based data, includes a converter for receiving voltage waveform input and generating a series of current pulses in response to the input voltage signal. A transmitter responsive to output of the converter is provided for transmitting the output onto a communication line terminated by a receiver. 
     Another embodiment of the invention provides an automatic system for adjusting series and shunt impedance of a transmitting system relative to changes in data and transmission medium by a circuit for measuring and correcting changes in series and shunt impedance of the line using references internal to the transmitter (voltage, current, impedance, and current range). A gain amplifier is used to control changes in impedance and signal current. Output voltage is kept at a reference level while output current is varied thereby controlling the impedance of the transmitter. The transmitter has a current source for supplying reference currents and a voltage source for supplying reference voltages and a gain controlling circuit for controlling a current signal within a range of values according to binary input data. 
     A common problem of other known modems is the deterioration of the transmission signal due to distortion effects over the transmission line. In effect, the transmission signal is not able to be identified because of the accompanying noise distortion. This invention is able to transmit significantly greater amounts of data than previous methods because it discriminates transmitted data from random distortion noise existing on the communication line. 
     A primary advantage of this invention is the provision of significantly increased amounts of data by being able to transmit and receive a low voltage signal amidst the accompanying random distortion noise and interference that was generally thought to be indeterminable. 
     A further advantage of this invention is the provision of significantly increased lengths of transmission than currently thought capable without the use of repeaters or amplifiers. 
     Another aspect of this invention is to transmit data at a low voltage and to further maintain this low voltage by monitoring and adjusting the current associated with the data signal. 
     It is further contemplated that the transmitter step of monitoring and adjusting the current includes the step of transmitting at least one reference/calibration pulse over the communication line and measuring the effects of line impedance on the current pulse. 
     These and other features of the present invention are discussed or apparent in the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram, in block diagram form, of a preferred embodiment of a device incorporating an automatic impedance tuner in accordance with the present invention coupled to a receiver via a communication line; 
     FIG. 2 is a partial simplified schematic diagram of the embodiment depicted in FIG. 1 including a converter, filter/regulator, amplifier and transmitter; 
     FIG. 3 is a graphical depiction of the modulated output of the converter of FIG. 2 after being partially modified by the filter/regulator; 
     FIG. 4 is a partial schematic of an alternative embodiment of the transmitter of FIG. 2; 
     FIG. 5 is a simplified block diagram of a system in accordance with the present invention including a data transmitter device, a transmission medium and a receiver; 
     FIG. 6 is a schematic diagram of an embodiment of the transmission medium shown in FIG. 5; 
     FIG. 7 is a schematic diagram of an alternative embodiment of the transmission medium shown in FIG. 5; 
     FIG. 8 is an expanded block diagram of the data transmitter device of FIG. 5 including a data generator connected to a transmitter; 
     FIG. 9 is an expanded block diagram of the data generator shown in FIG. 8 comprising a bit generator and a modulator; 
     FIG. 10 is a schematic diagram of an embodiment of a bit generator shown in FIG. 9; 
     FIG. 11 is a schematic diagram of an alternative embodiment of a bit generator shown in FIG. 9; 
     FIG. 12 is a schematic diagram of the modulator shown in FIG. 9; 
     FIG. 13 is a schematic diagram of the transmitter shown in FIG. 8; 
     FIG. 14 is a schematic diagram of a receiver shown in FIG. 5, the receiver comprising an input network, output network, amplifier IC 1 , amplifier IC 2 , and amplifier IC 3 ; 
     FIG. 15 is an expanded schematic diagram of the input network shown in FIG. 14; 
     FIG. 16 is an expanded schematic diagram of the output network shown in FIG. 14; 
     FIG. 17 is an expanded schematic diagram of amplifier IC 1  shown in FIG. 14; 
     FIG. 18 is an expanded schematic diagram of amplifier IC 2  shown in FIG. 14; and 
     FIG. 19 is an expanded schematic diagram of amplifier IC 3  shown if FIG.  14 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail, preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and it is not intended to limit the broad aspects of the invention to the embodiments illustrated. 
     Referring to FIG. 1, an automatic impedance tuner  5  is depicted having a converter/filter  10 , filter/regulator  12 , amplifier  14 , and transmitter  16 . The converter/filter  10  receives a digital voltage pulse signal  8  representing data. The input signal  8  is transformed by the converter  10  into a phase modulated current output  40  that is received by the filter/regulator  12 . 
     The filter/regulator  12  measures current change, limits the voltage range of the phase modulated current output  40 , and dampens ringing on the signal. In addition, the filter/regulator  12  differentiates the phase modulated current output  40 , adjusts for current gain and narrows the current pulses of the phase modulated current output  40 . Before being received by the amplifier  14 , the differentiated signal output  55  generated by the filter/regulator  12  is widened and returned to a timing similar to input data signal  8 . 
     The transmitter  16  adjusts the amplified current signal  57  generated by the amplifier  14  in response to filter/regulator  12 . Accordingly, the transmitter  16  provides a desired voltage and current for transmission to a receiver  20  via communication line  18 . Receiver  20  deciphers the transmission by detecting variations in the current received from the transmitter  16 . 
     Referring to FIG. 2, a further defined schematic diagram of a preferred embodiment of an automatic impedance tuner  5  in accordance with the present invention is provided. The tuner  5  includes the converter/filter  10 , filter/regulator  12 , amplifier  14 , and transmitter  16  of FIG.  1 . Accordingly, the same reference numbers are used, where appropriate, within both FIGS. 1 and 2. 
     The converter/filter  10  includes a common emitter transistor  24 , a filter capacitor  22 , two coupling feedback capacitors  34 ,  38 , and two current limiting resistors  26 , 28 . The input voltage pulse signal  8  received by the converter/filter  10  is filtered by capacitor  22  connected to the base of the first common-emitter transistor  24 . In part, the transistor operates as a cutoff circuit for keeping a sharp rise and fall time of the converter output  40 , and thus the output of the tuner  5 . Also, the first common-emitter transistor  24  provides a constant current reference through serially connected resistor  28  and adjustable resistor  26  wherein resistor  26  is coupled to a regulated power source  32  of about 8 volts and resistor  28  is attached to the collector  30  of the transistor. Preferably, the voltage potential at the collector  30  of the first common-emitter transistor  24  is approximately one-half the value of the voltage potential of the power source  32  with respect to ground, i.e., 4 volt. The collector  30  of the first common-emitter transistor  24  is fedback to its base through the two capacitors  34 ,  38  which are coupled together in series and operably connected at the junction of the capacitors to the output of the tuner  5 . This internal feedback controls the automatic impedance tuner&#39;s  5  current output relative to the load on the communication line  18  and the power source  32 . The coupling feedback capacitors  34  and  38  preferably are in a 2.2 to 1 ratio to modulate the input voltage signal  8  into a converted constant current signal received by the filter/regulator  12 . As a result of the charging and discharging of the capacitors  34  and  38 , the magnitude of each current pulse provided by the output  40  of the converter/filter  10  quickly rises to a peak, then falls to a plateau that is maintained for a time duration before the current magnitudes falling off rapidly. 
     Coupled to the converter&#39;s output  40  is the filter/regulator  12  comprising an AC and DC load that includes the load of the communication line  18 . The filter/regulator  12  consists of a measuring resistor  36 , a pair of clamping diodes,  44 ,  46 , a filter capacitor  54  and a differentiator. At the input of the filter/regulator  12 , the measuring resistor  36  is coupled between a pair of clamping diodes  44 ,  46 , preferably geranium. In particular, the resistor  36  is connected to the cathode of diode  44  and the anode of diode  46 . Moreover, the anode of diode  44  and the cathode of diode  46  are attached to ground. These diodes  44 , 46  are used to reduce noise on the converted output signal  40  by dampening voltage ringing and oscillations. The diodes  44 ,  46  clamp the converted data signal to a voltage level between 0.2 and −0.2 volt, or 0.4 volt peak-to-peak as shown in FIG.  3 . Moreover, a reference voltage range VR 1  is maintained at the junction between the diodes  44  and  46 . 
     In addition, the majority of the load provided by the filter/regulator  12  is AC. Part of the DC load of the filter/regulator  12  is fixed by the measuring resistor  36  and the pair of diodes  44 ,  46 . This fixed DC load is used as a reference load. 
     The data signal  40  also is differentiated within the filter/regulator  12  wherein the pulses of the received signal are narrowed. The differentiator is preferably comprised of a capacitor  48  in series with an adjustable resistor  50  for adjusting the output AC current level of the automatic impedance tuner  5  relative to the power source  32 . The pulses of the data signal are widened and returned to a timing similar to the original signal  8  by filter capacitor  54 . Moreover, resistor  50  provides for adjusting current gain. 
     The differentiated current signal  55  from the filter capacitor  54  of the filter/regulator  12  is received by the amplifier  14  which includes a second common-emitter transistor  52  for amplifying the differentiated current signal and a voltage limiting pull-up resistor  56  for limiting the voltage at the collector of the second common-emitter transistor  52 . Preferably, the collector has a voltage of about 6 volt (i.e., close to the threshold turnoff) and is coupled to the transmitter  16 . Via capacitor  64 , the switching of shunt transistor  52  is effected by changes in the voltage at the tip transmitter  18  for maintaining a substantially constant voltage level at the tip transmitter. 
     The transmitter  16  includes a coupling capacitor  54 , a pair of clamping diodes  58 ,  60  and a resistor-capacitor  62 ,  64  combination. The coupling capacitor  54  at the input of the transmitter  16  is attached to the output of the amplifier  14 . The coupling capacitor  54  widens the pulses of the amplified current signal  57 . Coupled between the filter capacitor  54  and the adjustable resistor  62  are two clamping diodes,  58 ,  60 , preferably of type silicon, for maintaining the amplified current signal  57  within a voltage range VR 2  between 0.7 and −0.7 volt, 1.4 volt peak-to-peak. The adjustable resistor  62  controls the voltage level and the AC current through a capacitor  64  while the two clamping diodes  58 ,  60  control the DC offset relative to ground. The adjustable resistor  62  and capacitor  64  adjust the voltage level on the communication line to approximately 1 volt, peak-to-peak. Prior to reaching the communication line, a diode-capacitor combination filters the AC portion of the signal from negative going noise spikes and a diode-resistor combination filters the DC portion of the signal from positive going noise spikes. 
     In an alternative embodiment, depicted in FIG. 4, the collector of the second common-emitter transistor  52  within the transmitter  14  is attached to two capacitors  54 ,  64  in series and then to a line-side select switch  80 . Signal transmission can be placed on either the Tip  4  or the Ring  5  lines of the twisted copper pair of wiring, however, use of the Tip  4  line is preferred. Use of a line-side select switch  80  is connected to the junction of two diodes,  70 ,  72 . If the Tip  4  line is going to be used as the output, a diode  72  and a capacitor  74  filter the AC portion of the signal from negative going noise spikes. A diode  70  and a resistor  76  are used to filter the DC portion of the positive going noise spikes. If the Ring  5  line is going to be used as the output, then a diode  68  and capacitor  74  are used to filter the AC portion of the signal from negative going noise spikes while another diode  66  and a resistor  76  filter the DC portion of the positive going noise spikes. 
     Turning to FIG. 5, a simplified block diagram is depicted of a system in accordance with the present invention. The system  110  includes a data transmitter device  112 , a data transmission medium  114 , and a data receiver  116 . The data receiver  116  receives data signals transmitted from the transmitter  112  across the transmission medium  114 . 
     In FIG. 6, the transmission medium  114  is modeled to provide conventional characteristics found in telephone transmission cables or the like that do not include a significant amount of inductance. The transmission medium receives input signal pair  132  and  172  and provides corresponding output signal pair  188  and  190 . In an alternative embodiment shown in FIG. 7, the transmission medium  114  can be modeled to provide characteristics found in transmission mediums having, for example, about 15 mH of inductance as found in many conventional preexisting transmission mediums. 
     As shown in FIG. 8, the data transmitter  112  preferably includes a data generator  118  and a transmitter  120  operably coupled together. In a preferred embodiment shown in FIG. 9 for testing the circuitry, the data generator  118  includes a bit generator  122  and a modulator  124 . The bit generator  122  provides a data signal  126  represented as a series of voltage pules preferably in the range of about 0 to 5 volt. As shown in FIG. 10, the bit generator  122  can consist of a counting circuit responsive to a digital reference clock signal  128  wherein a series of digital data signals  126  are provided corresponding to binary numeric values and increasing in binary numeric magnitude at a constant incremental rate. Alternatively, in another embodiment for testing shown in FIG. 11, the bit generator  122  can consist of a counting circuit responsive to a digital reference clock signal  128  for providing digital data signals  126  corresponding to numeric values and decreasing in binary numerical magnitude at a constant incremental rate. 
     As shown in FIG. 12, the digital data signals  126  from the bit generator  122  along with digital reference clock signal  128  are received by the modulator  124 . In response to these signals, the modulator  124  generates a modulated digital data signal  130  comprising the digital data signals  126  added to the clock signal  128 . 
     The modulated digital signals  130  are received by the transmitter  124  for conversion and transmission across the transmission medium  114  to the receiver  116 . As shown in FIG. 13, the transmitter  124  is similar to that shown in FIG.  2  and described above. In particular, the transmitter  124  receives the digital signals  130  and converts them into current pulses while maintaining a substantially constant voltage level on the output  132 . Preferably, the voltage level is about 1 volt. 
     In particular, the digital signals  130  are fed to the capacitor  134  attached to the base of transistor  136 . This transistor  136  is a constant current reference through resistor  138  and adjustable resistor  139  to Vcc, preferably about +8V. The transistor  136  has feedback from it&#39;s collector to it&#39;s base through two capacitors  140  and  142  in series. This controls the transmitter current relative to the load and Vcc. At the junctions of capacitors  140  and  142  is an AC and DC load including the line, which the majority of the load being AC. Part of the DC load at this junction is fixed by a resistor  144  and diodes  146  and  148 . The fixed DC load is used as a reference load. The diodes  146  and  148  clamp the peaks to 0.7 V positive and negative going resulting in a 1.4V peak to peak output. The junction of  144 ,  146  and  148  goes to a capacitor  150  and then to an adjustable resistor  152 . This adjustable resistor  152  adjusts the output AC current level of the transmitter  124  relative to Vcc then goes to a capacitor  154  and then to the base of a transistor  156 . The transistor&#39;s collector goes to capacitor  158  coupled to diodes  160  and  162  for clamping the peaks to 0.7v positive and negative going resulting in a 1.4V peak to peak output  164 . Also attached to the output  164  is an adjustable resistor  166  for controlling the voltage level and the AC current through a capacitor  168 . The collector of transistor  154  also is coupled to a resistor  170  attached to Vcc for limiting the voltage that the transistor will reach when fully turned on. Furthermore, serial connected diode  172  and resistor  174  are coupled between ground and output  132  for filtering the DC portion of positive going noise spikes. 
     As shown in FIG. 14, the receiver  116  includes an input network  178 , an output network  180 , and a plurality of integrated IF amplifiers  182 ,  184 , and  186 . Referring to FIGS. 5 and 16, TIP and the RING signals  132  and  136  are transmitted across the transmission medium  144  and the input network  178  receives corresponding TIP and RING signals  188  and  190 , respectively. In response to signals  188  and  190 , the input network  178  filters out noise to provide filtered data output signal groups  192  and  194 . 
     The filtered signal groups  192  and  194  are received by IF amplifiers  182  and  184 , respectively, for amplifying the signals and passing them to the output network  180  where the signals are mixed together and amplified by amplifier  186  to produce a noise reduced digital data output signal  196  corresponding to the digital data input  126  from the data generator  122 . 
     Twisted-pair phone lines are disclosed as a preferred embodiment only due to their prevalence in the global telecommunication infrastructure. It is contemplated that advantages may be had employing the basic concepts of the invention in transmission of data over shielded coaxial cable lines, category 5 lines, twisted-pair copper lines, etc. It is even contemplated that the present invention may be advantageously employed with wireless communication mediums such as broadcast in air, since signal attenuation, concerns also apply to this transmission medium. 
     “Transmission medium,” as used herein relates to a communication line or an electromagnetic signal path from a first device to a second device being physically and spatially remote from the first. “Communication line” as used herein relates only to one or more conductors and the like used for transmitting data from a first device to a second device being physically and spatially remote from the first. “Remote,” means, that neither the first nor the second device share the same chassis, housing, or support structure. In its most concrete and conventional form, remote would contemplate one modem communicating with another over conventional telecommunication lines, although it is not intended to be so limited. In short, the present invention addresses data transmission problems presently faced by telecommunications industry, Internet, and local area networks in communication between remote devices. 
     Presently it is believed that one of the most needed areas for the invention is for data transmission along a “communication line” from homes and businesses to and from a telecommunications central switching office (“CO” or “switching office”). This is where a bulk of the twisted-pair copper communication line infrastructure is deployed. 
     It should also be understood that only preferred embodiments of the present methods and circuits are described herein. It is intended that changes and modifications may be made in the embodiments disclosed without departing from the true scope and spirit of the present invention as defined by the appended claims. 
     For example, it should be understood that the embodiments only illustrate converting input voltage signals because most devices today provide data in this form, e.g. computers. However, the invention contemplates transmission of current pulse which do not have to be converted to the extent a data device may, in the future, provide output data as current pulses to begin with. In such case, the present invention may be employed without conversion related to voltage/current but only for data encoding schemes and the like as may be desired for transmission purposes.