Electronic digital logic circuitry – Interface – Current driving
Reexamination Certificate
1998-12-09
2001-02-06
Tokar, Michael (Department: 2819)
Electronic digital logic circuitry
Interface
Current driving
C326S086000, C326S030000, C326S021000, C326S022000, C326S026000, C326S090000, C326S082000
Reexamination Certificate
active
06184717
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a signal transmitter for transmitting digital logic signals and a complementary receiver, and more particularly to a digital logic transmitter that generates one or more reference signals, to be used by the receiver to establish threshold levels for digital HI and LO signals.
BACKGROUND OF THE INVENTION
Digital electronic systems typically utilize very large scale integrated circuit (“VLSI”) blocks. VLSI blocks, are interconnected to each other within an electronic system by electronic conductors that act as transmission lines. Digital HI and LO signals are represented by two distinct voltage levels presented on the conductors. A “driver” forming part of one VLSI block couples a transmitting VLSI block to the transmission lines. Similarly, a “receiver” forming part of a receiving VLSI block, couples the receiving VLSI block to the lines. Each driver and receiver typically comprises a plurality of transistors formed on the respective VLSI blocks.
The transistors forming the drivers and receivers are coupled to ground points on the VLSI blocks. These ground points, however, are not at the same potential as the external ground potential of the VLSI packages. Drivers are coupled to the external ground connection through a package impedance. This package impedance typically has resistive, inductive, and capacitive components and is therefore a source of electrical noise present when a driver output switches from LO to HI or HI to LO. This noise is typically referred to as a “ground bounce”.
At the receiver, binary HI and LO signals are typically distinguished by their voltage levels relative to the receiver package ground. Signals that exceed a threshold voltage level represent a digital HI while signals that fall beneath another threshold voltage represent a digital LO. As will be appreciated, the presence of noise from the transitioning signal at the transmitter, may cause a signal not intended to cross a threshold to cross this threshold, as sensed at a receiver. This, in turn, may lead to errors in the received signal.
Numerous digital drivers and receivers address this problem. For example, the gunning transceiver logic (“GTL”) family as more particularly described in U.S. Pat. No. 5,023,488 uses low voltage swings that reduce transient effects of parasitic impedances, including package impedances. As well, this patent discloses clamping the drain to source of a GTL driver to reduce the rate at which current is drawn so as to provide increased damping for noise due to transient voltages.
Still other logic families use differential outputs. As the effect of parasitic impedances is the same for both outputs of a differential pair, differential signals naturally reject common mode noise. Differential signals, however, require double the number of outputs for a transmitting VLSI block; double the number of transmission lines interconnecting the transmitting VLSI block to the receiving VLSI block; and double the number of inputs at the receiving VLSI block. As will be appreciated, it would often be desirable to eliminate these extra inputs, outputs and interconnects.
Accordingly, an alternative to known approaches to reduce the effects of package impedance in digital transmitters and receivers is desirable.
SUMMARY OF THE INVENTION
In accordance with the present invention a transmitter and complementary receiver use HI and/or LO reference signals generated at the transmitter, and transmitted to the receiver. The reference signals are used at the receiver to account for noise components in received signals that are representative of digital HI or LO signals.
In accordance with an aspect of the invention, there is provided a signal transmitter block formed as part of an integrated circuit. The transmitter block transmits digital signals to a receiver. The transmitter block includes several signal drivers, each for generating output voltages at a signal driver output, that when measured relative to a ground point on the integrated circuit are representative of digital HI and LO signals. A first reference driver, for generating at a first reference output an output voltage that when measured relative to the ground point, corresponds either a digital HI signal; or a digital LO signal, forms part of the block. The first reference driver and the signal drivers are electrically interconnected to the ground point on the integrated circuit block. The ground point is further interconnected through an impedance on the integrated circuit block to a system ground connection for the integrated circuit, so that current flowing from and to the system ground connection through the ground point to the signal drivers and the first reference driver flows through the impedance.
In accordance with another aspect of the invention, a digital signal receiver block having receiver block outputs for generating digital HI and LO signals, includes several comparators. Each comparator has a signal input for receiving a voltage signal representative of one of a digital HI signal and LO signal and a noise signal; an output interconnected with one of the receiver block outputs; and a first reference input for receiving a reference voltage signal including a signal indicative of a digital LO signal, and a noise signal. The first reference inputs of the several comparators are interconnected so that each of the reference inputs receives the same reference voltage signal. Each of the comparators is adapted to produce at its output a signal representative of a digital LO signal when a voltage at its signal input is less than a threshold voltage derived from a reference voltage at its first reference input.
In accordance with yet another aspect of the present invention, there is provided a method of transmitting and receiving several signals representative of digital HI and LO signals from a transmitter to a receiver. The method includes the steps of a. concurrently transmitting the several signals, each having a voltage level representative of one of a digital HI and LO signal and a noise signal from a transmitter to a receiver; b. transmitting a reference signal comprised of a signal having a voltage level representative of a HI signal and a noise signal to the receiver; c. receiving the several signals and the reference signal at the receiver; d. comparing the reference signal to each of the several signals; e. outputting a signal representative of a digital HI signal at the receiver, for each of the several signals that exceeds a threshold voltage derived from the reference signal.
Advantageously, the invention provides rejection of noise signals without the use of differential signals.
Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
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Nortel Networks Limited
Tan Vibol
Tokar Michael
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