Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
1998-11-23
2001-01-16
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C326S082000, C375S258000
Reexamination Certificate
active
06175255
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of communications, and in particular, to line drivers.
2. Related Art
A local-area network (“LAN”) is a communication system that enables personal computers, work stations, file servers, repeaters, data terminal equipment (“DTE”), and other such information processing equipment located within a limited geographical area such as an office, a building, or a cluster of buildings to electronically transfer information among one another. Each piece of information processing equipment in the LAN communicates with other information processing equipment in the LAN by following a fixed protocol (or standard) which defines the network operation. Information processing equipment made by different suppliers can thus be readily incorporated into the LAN.
The ISO Open Systems Interconnection Basic Reference Model defines a seven-layer model for data communication in a LAN. The lowest layer in the model is the physical layer which consists of modules that specify (a) the physical media which interconnects the network nodes and over which data is to be electronically transmitted, (b) the manner in which the network nodes interface to the physical transmission media, (c) the process for transferring data over the physical media, and (d) the protocol of the data stream.
IEEE Standard 802.3, Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications, is one of the most widely used standards for the physical layer. Commonly referred to as Ethernet, IEEE Standard 802.3 deals with transferring data over twisted-pair cables or co-axial cables. The 10 Base-T protocol of IEEE Standard 802.3 prescribes a rate of 10 megabits/second (“Mbps”) for transferring data over twisted-pair cables.
The constant need to transfer more information faster, accompanied by increases in data processing capability, necessitated an expansion to data transfer rates considerably higher than the 10-Mbps rate prescribed by the 10 Base-T protocol. As a consequence, a protocol referred to as 100 Base-T was developed for extending IEEE Standard 802.3 to accommodate data moving at an effective transfer rate of 100 Mbps through twisted-pair cables. Under the 100 Base-T protocol, certain control bits are incorporated into the data before it is placed on a twisted-pair cable. The result is that the data and control signals actually move through a twisted-pair cable at 125 Mbps.
In expanding IEEE Standard 802.3 to the 100 Base-T protocol, there are various situations in which it is desirable that the transmitter be capable of using one driver to transmit data at both the 100 Base-T rate and the lower 10 Base-T rate. Accordingly, it is preferable to use a line driver capable of driving both 10 Base-T and 100 Base-T signaling.
In particular, one set of information processing equipment should be capable of driving data moving at the 10 Mbps (“Meg”) rate or the 100 Meg rate without having to make any adjustments when the data transfer rate changes from 10 Meg to 100 Meg and vice versa.
FIG. 1
illustrates the data transmit path
100
of communication in the LAN operating in 100 Base-T. During data transmission, a communication unit operating on the LAN, such as a computer
117
, generates a data signal T
1
which is converted into differential form for transmission on the twisted pair cable
103
. For 10 Base-T transmission, this data signal T
1
is Manchester coded
101
to reduce electromagnetic interference and to produce square wave pulses. These waves then go through a waveshaping filter to generate filtered differential data signals T
1
+/−.
In this description a pair of differential signals means two signals whose current waveforms are out of phase with one another. The individual signals of a pair of differential signals are indicated by reference symbols respectively ending with “+” and “−” notation-e.g., S+ and S−. The composite notation “+/−” is employed to indicate both differential signals using a single reference symbol-e.g., S+/−.
For 100 Meg transmission, scrambler
119
scrambles data signal T
1
and converts data signal T
1
to differential format. Encoder
121
MLT-
3
codes the data signal to generate trinary differential signals T
2
+/−. A 10 Meg amplifier signal driver
107
and a 100 meg amplifier signal driver
109
take these differential signals T
1
+/− and T
2
+/−, respectively, and generate voltage-sourced differential signals T
10
+/− and T
20
+/− respectively, to drive a primary load
105
and to transmit them on twisted pair cable
103
.
Transformer
111
has a primary winding
111
A and a secondary winding
111
B which isolate the twisted-pair cable
103
from the circuitry producing the transmit signals. Primary winding
111
A terminates at a primary load
105
and secondary winding
111
B terminates at a secondary load
113
. Secondary load
113
couples to a connecting unit
115
, which couples to twisted-pair cable
103
. Primary winding
111
A couples to a resistive load
105
. It is across this resistive load
105
that either sine wave 10 Base-T signaling or MLT-
3
100 Base-T signaling must be created.
Recently, current driven amplifiers have been used to drive both the 10 Base-T and the 100 Base-T signalling. Now that it also has become necessary for many commercial integrated circuits to operate at less than the conventional 5 volt power supply voltage, such as 2.5 volts, these line driver circuits must operate over a power supply range from over 5 volts down to 2.5 volts and less. However, although the supply voltage dropped from 5 volts to 2.5 volts, the 10 Base-T signaling mode still requires a 5-volt peak-to-peak output voltage.
FIG. 2
illustrates a conventional line driver
200
capable of driving both 10Base-T and 100Base-T signaling. Typically, as the circuits move down to lower supply voltages, there is not enough headroom for current sources I
21
-I
23
to operate. Thus, transformer T
2
operates in a 1:2 voltage step-up mode with respect to the differential data signals, to boost output voltage Vout to 5 volts peak-to-peak. The difference in voltage between the output nodes V+, V− on the output terminals form the pair of differential signals.
Line driver circuit
200
includes a resistive load RL coupled between output nodes V+, V− and to the primary winding of transformer T
2
. The secondary winding of transformer T
2
couples to a termination resistor R
2
. Typically, this termination resistor is approximately 100 ohms as required by the Institute of Electrical and Electronics Engineers (IEEE). Line driver circuit
200
also includes a 10Base-T sub-circuit
201
to generate a 5 volt peak-to-peak output signal Vout across resistive load RL, and a 100Base-T sub-circuit
202
to generate a 2 volt peak-to-peak output signal Vout across resistive load RL. The 10Base-T sub-circuit
201
includes switches SW
21
, SW
22
, and current sources I
21
, I
22
each of which provide 100 milliamperes (mA) of current. The 100Base-T sub-circuit
202
includes switches SW
23
-SW
26
and current source I
23
which provides 40 mA of current. The six switches SW
21
-SW
26
are controlled by input signals IN
21
-IN
26
, respectively, and direct current through load resistor RL as indicated by arrows A and B. Typically, these input signals IN
21
, IN
22
are rail-to-rail voltage swings, and input signal IN
21
is the inverse of input signal IN
22
.
In 10Base-T operation, input signals IN
27
, IN
28
are half-wave rectified signals which are 180 degrees out of phase from one another. These signals are applied to current sources I
21
, I
22
, respectively, such that only one of the two current sources is active at a time. In addition, input signals IN
21
, IN
22
are applied to switches SW
21
, SW
22
such that one of the switches SW
21
, SW
22
closes and the other opens to steer current through resistive load RL thereby generatin
Callahan Timothy P.
Englund Terry L.
Limbach & Limbach L.L.P.
National Seniconductor Corporation
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