Pulse or digital communications – Repeaters – Testing
Patent
1989-04-14
1991-02-19
Safourek, Benedict V.
Pulse or digital communications
Repeaters
Testing
178 63R, 178 63A, 178 661, 333217, 375 36, H04B 336, H04L 2502
Patent
active
049950541
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF THE INVENTION
Many well known and standardised systems exist for serial data transmission. These systems fall into several categories, each of which suffers from a number of drawbacks when used for transmitting data on long lines. The most common form of low speed aerial data transmission is a current limited line transmitting system typified by the well known RS232 standard which suffers from the drawbacks that its transmission distance is limited, that its power consumption increases in proportion to the line length and that it is not easily adapted for multi-station use. The much older current loop standard as used by teletype machines does not suffer these latter problems, but introduces reliability problems as a result of the need to connect the transmitting switches in series with the lines, and as a result of losses and voltage spikes caused by line inductance. Another commonly used data transmission system involving the use of matched impedance termination allows high speed, but suffers from the drawback of energy losses in the terminating resistors, and the resulting need for the transmitting station to make good these losses.
This invention provides a means of transmitting data where low power consumption at any or all stations is an important factor, or where a simple means of electrically isolating the transmitting station from the line is a requirement. These requirements are important where electrical safety is needed, where noise immunity is important, and also where power supply is limited as in the case of battery powered equipment or where power is to be drawn from existing data lines or from an RS232 port on a personal computer. This invention also provides for controlled voltage slew rates, thus minimizing radiated electrical noise and timing errors.
All electrical lines used for transmitting data have distributed capacitance and inductance associated with them. In order to achieve an acceptable level of immunity to outside interference an adequately high signalling energy must be used. In existing data transmission systems the energy required is usually provided by an energy source associated with the transmitter.
The novelty of this invention consists of using the energy stored in the data lines and associated circuitry to signal data state transitions via the data lines by means of a switched resonant circuit. The invention resides in the use of an inductance-capacitance resonant circuit wherein the inductance may be that of the data lines alone or with additional inductance and wherein the capacitance may be that of the data lines alone or with additional capacitance and wherein the configuration of the resonant circuit may be altered by means of the operation of electronic switches included within the circuit. The transmission of data does not require loss or gain of energy in the resonant circuit and is achieved through appropriate switching of the said electronic switches to achieve a reversal of the polarity of the charge stored in the said capacitance thus signalling a change in the transmitted data state. Since any practical embodiment of the invention will involve some losses during normal operation a regenerative circuit is required. The momentary nature of the switch closure means that the data lines are effectively disconnected except during the period of line state transition. This allows multiple transmitting stations to be connected to a single set of data lines for "Party-line" or "Multi-drop" operation without interference by inactive transmitting stations.
In order to provide a clearer understanding of this invention, reference is taken to the following description in conjunction with accompanying drawings, in which:
FIG. 1 is a schematic drawing showing a typical set of lines with connected transmitting and receiving stations.
FIG. 2 is a schematic drawing showing an embodiment of the invention where the resonant circuit consists of lumped inductance and capacitance.
FIG. 3 is a schematic drawing of an embodiment of the invention where the switching
REFERENCES:
patent: 3202763 (1965-08-01), Gaunt, Jr.
patent: 3303286 (1967-02-01), Schlichte
patent: 3369075 (1968-02-01), Yourke et al.
patent: 4383313 (1983-05-01), Sbuelz
patent: 4398178 (1983-08-01), Russ et al.
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