Pulse or digital communications – Pulse width modulation
Reexamination Certificate
1997-10-01
2001-02-06
Chin, Stephen (Department: 2734)
Pulse or digital communications
Pulse width modulation
C327S026000, C327S172000, C329S312000
Reexamination Certificate
active
06185252
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for decoding a digital signal, a bus system and a peripheral unit therefor.
BACKGROUND INFORMATION
A method for decoding a digital signal is already known where the digital signal is-a pulse-width modulated signal. The signal can assume two states: a high signal level and a low signal level. In pulse-width modulation, a certain time (total pulse width) is provided for each bit to be transferred. The signal first assumes the low level and then the high level during the total pulse width, with the duration of the high signal level constituting either one-third or two-thirds of the total pulse width. Other proportions are, of course, also conceivable. The first case corresponds to a coded binary zero, the second case corresponds to a binary one. This bit is decoded by measuring the signal level at a point approximately mid-way through the total pulse width. For this purpose, the decoder is provided with an oscillator to reliably measure the middle of the total pulse width.
Including an oscillator increases the cost of the decoder. If longer bit streams are to be decoded, the oscillator must have high accuracy and the total pulse widths of the individual bits must be reproducible to a high degree. This requirement makes the use of high-precision and accurately adjusted oscillators necessary both in the encoder and the decoder.
Furthermore, unpublished German Patent Application No. 196 162 93.9 discloses a bus system for transmitting messages between a controller and a peripheral unit, wherein the controller sends messages of high and low urgency to the peripheral unit. The high-urgency messages have a greater amplitude and data transmission rate than the low-urgency messages. The messages consist of digital signals, where a binary zero corresponds to a low signal level, and a binary one corresponds to a high signal level.
SUMMARY OF THE INVENTION
An advantage of the process according to the present invention is that no oscillator is needed in the decoder. The signal
oise ratio is also improved and the error rate of the data transmission is reduced due to the integral analysis of the entire signal instead of a discreet point of the signal. In addition, decoding is independent of the total pulse width and the corresponding data transmission rate.
The bus system, the peripheral unit, and the device according to an exemplary embodiment of the present invention have the advantage that they have a simpler and therefore less expensive design. The peripheral unit has the further advantage that a single decoder is provided for the different data transmission rates.
It is particularly advantageous if the input signal of the comparator is manipulated so that the binary zero and binary one differ by having different polarities. This criterion is self-normalizing in the sense that it is independent of the total pulse width. Thus, the decoder can decode digital words independent of the data transmission rate, and also when the total pulse width varies from bit to bit.
After adding a third signal to the signal to be decoded, it is also advantageous to add a fourth signal so that the signal to be decoded preserves its polarity during the total pulse width of a bit. Adding the fourth signal avoids the need to send a polarity bit to the VFC.
According to the present invention, it is also particularly advantageous to transmit high-urgency and low-urgency messages in the bus system, with the former having a higher amplitude than the latter, so that the higher-urgency messages automatically overwrite the lower-urgency messages. It is also advantageous to keep the total pulse width of the higher-urgency messages lower than the pulse width of the low-urgency messages to increase the transmission rate for the high-urgency message. A better EMC is achieved for the low-urgency messages due to their larger total pulse width.
According to an exemplary embodiment of the present invention, it is advantageous to design of the bus system of the present invention as an ignition bus for an air bag system where the low-urgency messages are diagnostic queries and the high-urgency messages are ignition commands, as such an air bag system has a flexible design and is easy to expand and/or repair.
REFERENCES:
patent: 3864583 (1975-02-01), Fiorino
patent: 3939304 (1976-02-01), Ribes
patent: 4265200 (1981-05-01), Wessel et al.
patent: 4408166 (1983-10-01), Moeller
patent: 4853623 (1989-08-01), Sterler et al.
patent: 5363405 (1994-11-01), Hormel
patent: 5832397 (1998-11-01), Yoshida et al.
patent: 26 53 046 (1978-05-01), None
patent: 28 45 598 (1979-04-01), None
Chin Stephen
Ghayour Mohammad
Kenyon & Kenyon
Robert & Bosch GmbH
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