Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific quantity comparison means
Patent
1998-12-28
2000-10-10
Ballato, Josie
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific quantity comparison means
307127, 307146, 327325, 333 12, 333 24R, H02H 318, H03K 19086
Patent
active
061308129
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a protection circuit for high speed signal communication using PECL (Positive Emitter Coupled Logic) technology.
DESCRIPTION OF RELATED ART
ECL (Emitter Coupled Logic) devices are employed in systems requiring very fast signal processing since the power dissipation of ECL devices is constant over a wide signal frequency range. ECL devices are especially attractive for driving long transmission lines and for reduction of system clock skew (see "Designing with PECL (ECL at +5.0V)", Motorola Application Note AN1406). Integrating ECL devices in conventional TTL (Transistor--Transistor Logic)/CMOS (Complementary Metal Oxide Semi-conductor) design is sometimes desirable. Then it is advantegous to use PECL (Positive Emitter Coupled Logic) devices. PECL devices are ECL devices supplied by a positive (+5V) power supply. Thus, PECL devices can be implemented using the same power supplies as TTL/CMOS devices.
PECL devices are often employed in differential applications such as differential PECL driver-receiver connections as they comprise a differential amplifier input structure and complementary outputs. One possible problem with a PECL driver-receiver connection is when the driver is supplied with power while the receiver is not supplied with power. The base-collector junctions of the input transistors of the PECL receiver will be forward biased and consequently conduct current, which current can be very high (depending on the resistance of the collector load resistor). This will lead to high power dissipation in the driver and also a risk for damages in the driver as well as in the receiver.
SUMMARY OF THE INVENTION
The object of the invention is to eliminate the problem with the large power dissipation and the risk for damages in the driver due to the currents flowing towards the receiver and for receiver degradation due to high currents flowing in the base-collector junctions of the differential pair input transistors of the receiver.
This is accomplished with a protection circuit which, according to the invention, comprises a simple passive network consisting of two diodes and two resistors. The diodes are connected in the respective wire between the driver and the receiver and in such manner that when the power supply of the receiver is switched off, the diodes are reverse biased and effectively block all current flow from the driver to the receiver. When the power supply of the receiver is switched on, the diodes are forward biased, which is accomplished in that the resistors are connected between the receiver power supply and the respective diode.
The diodes are interconnected in the respective wire with the cathodes of the diodes connected to the respective output terminal of the PECL driver and the anodes of the diodes connected to the respective input terminal of the PECL receiver, and the resistors connected between the PECL receiver power supply and the anode of the respective diode. If the driver transmits signals over e.g. a transmission line the diodes are preferably connected between the driver and the transmission line.
The protection circuit according to the invention avoids the problems mentioned above by effectively blocking all DC current flow from the driver to the receiver.
An advantage of the invention is that it is easy to implement.
A further advantage of the invention is that it is applicable with both series and parallel termination scheme.
Yet another advantage is that a protection against short circuits is provided when connecting the diodes between the respective output terminal of the PECL driver and the respective wire of the transmission line.
Still another advantage of the invention is that mismatching problems in the transmission line can be avoided when connecting a first and a second capacitor in parallel with the respective diode. Hence, the circuit does not introduce any modification in the propagation of the signals.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in greater detail
REFERENCES:
patent: 3617771 (1971-11-01), Lee
patent: 4321429 (1982-03-01), Takatsuki et al.
patent: 4408248 (1983-10-01), Bulley et al.
patent: 4661878 (1987-04-01), Brown et al.
patent: 5087833 (1992-02-01), Sugai
patent: 5335134 (1994-08-01), Stein et al.
patent: 5541527 (1996-07-01), Hae-Ting Ma
patent: 5640127 (1997-06-01), Metz
Calcaterra Luca
Corvasce Giorgio
Ballato Josie
Huynh Kim
Telefonaktiebolaget LM Ericsson
LandOfFree
Protection circuit for high speed communication does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Protection circuit for high speed communication, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Protection circuit for high speed communication will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2261500