Electronic digital logic circuitry – Tri-state
Reexamination Certificate
2001-09-20
2003-12-30
Tran, Anh (Department: 2819)
Electronic digital logic circuitry
Tri-state
C326S082000, C326S057000
Reexamination Certificate
active
06670827
ABSTRACT:
This invention relates to a tri-state driver arrangement in accordance with the pre-characterising portion of claim 1, and in particular a tri-state driver arrangement, which can be used to send data from a subscriber via a communications bus to a further subscriber using an interface, for example in accordance with the RS-485 standard.
The RS-485 standard is used to define the transmission of information across different communications busses. Here, the communications bus consists of a two-wire cable to which the individual bus subscribers are connected in parallel and where several bus subscribers are able to receive data sent from another bus subscriber at the same time (so-called “multi-drop” configuration). On account of the high number of node points and the need for a reliable transmission of data or signals, all bus subscribers are potentially isolated from the communications bus. Furthermore, the line drivers or output drivers associated with the individual bus subscribers must have tri-state characteristics, i.e. along with the states “L” and “H”, they can take a third, high-impedance state. If a bus subscriber is active, i.e. if the output driver associated with this bus subscriber is sending data, all the other bus subscribers must be in the receive mode and disconnect their output drivers from the communications bus, i.e. switch to the above-mentioned tri-state condition.
FIG. 5
shows an example of a potentially isolated RS-485 interface according to the state of the art. The RS-485 interface incorporates a tri-state driver
12
acting as a transmitter with an output driver
16
, which is connected to a two-wire bus-cable A, B. Transmitted data TxD are fed to the tri-state driver
12
and amplified by means of an amplifier
14
. A fast optocoupler
15
transfers the transmitted data with potential isolation to the output driver
16
. Furthermore, an activation or enable signal is fed to the tri-state driver
12
and amplified by means of an amplifier
17
. A slow-acting optocoupler transfers the enable signal to the output driver
16
in the form of an appropriate voltage U
EN1
via a further amplifier
19
with potential isolation, whereby the output driver
16
is activated or deactivated depending upon the value of the voltage U
EN1
, i.e. switched to the tri-state condition. Furthermore, the RS-485 interface incorporates a receiver
13
, which is also connected to the two-wire bus-cable A, B, whereby an amplifier
20
receives and amplifies data transmitted from another subscriber, which are output as received data RxD via a further fast optocoupler
21
and a driver
22
.
As can be seen from
FIG. 5
, the RS-485 interface or the appropriate tri-state driver
12
needs two channels, each with an optocoupler, for sending the transmitted data TxD and for activating/deactivating the output driver
16
, i.e. the number of components required and the driver power are relatively high.
This invention is therefore based on producing a tri-state driver arrangement, which enables the potentially isolated transmission of signals with minimum driver outlay.
This problem is solved according to the invention by a tri-state driver arrangement with the characteristics of claim
1
or
11
. The sub-claims each define preferred and advantageous embodiments of this invention.
According to one embodiment, the tri-state driver arrangement according to the invention uses a magnetic coupler for the potentially isolated transmission of signals between the input and the output of the tri-state driver arrangement, which can be formed in particular due to a sensor, which works on the principle of the so-called GMR (Giant Magnet Resistor) effect. Likewise, however, other types of magnetic coupler can also be used, such as for example, Hall sensors, signal transformers, etc.
Due to the use of the magnetic coupler, only one channel is required for transmitting information or data and for the activation/deactivation of the output driver of the tri-state driver arrangement. Compared with the state of the art described above, this means a saving on components and driver power. Furthermore, the use of the magnetic coupler allows a saving to be made on the area of silicon required as well as the bonding effort when the tri-state driver arrangement according to the invention is used in a potentially isolated RS-485 interface and this potentially isolated RS-485 interface is integrated into a housing.
Furthermore, a suitable logic or control is proposed within the framework of this invention, which evaluates the output signal from the coupler, in particular the output voltage from the coupler, with respect to a pre-defined limiting range and, depending on this, produces an activation or enable signal for the output driver in order to activate or deactivate this for transmitting data, i.e. to switch it to the high-impedance tri-state condition. In doing so, it is particularly advantageous if the enable signal mentioned is fed to the output driver via a smoothing filter with an appropriate time constant so that the output driver is not unnecessarily switched off for short intervals of time. The procedure suggested within the framework of this invention for evaluating the output signal of the coupler in order to activate the output driver for transmitting data or to switch it to the tri-state condition and thus deactivate it dependent upon this, can be achieved particularly easily and without great expense and, in principle, is independent of the type of coupler used in each case, as long as this has a sufficiently linear output characteristic, which makes it possible to evaluate the output signal of the coupler in accordance with the invention.
This invention is particularly suitable for use in potentially isolated RS-485 interfaces. Of course however, this invention can also be used wherever it is required to transmit potentially isolated signals or data between an input and an output using a tri-state characteristic.
This invention is described in more detail below in the light of preferred embodiments with reference to the attached drawing.
REFERENCES:
patent: 5815528 (1998-09-01), Koga et al.
patent: 6054780 (2000-04-01), Haigh et al.
patent: 6262600 (2001-07-01), Haigh et al.
patent: 197 18 420 (1998-11-01), None
Corless Peter F.
Edwards & Angell LLP
Infineon - Technologies AG
Silvia David J.
Tran Anh
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