Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2000-04-05
2001-10-23
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C326S058000
Reexamination Certificate
active
06307408
ABSTRACT:
TECHNICAL FIELD
The present invention relates, generally, to methods and apparatus for creating a power down state in a circuit. More particularly, the present invention relates to a technique for powering down a line driver in a bidirectional transceiver while maintaining matched impedance without static power consumption.
BACKGROUND OF THE INVENTION
Communications devices such as modems, cable modems, digital subscriber line (DSL) modems and the like are becoming increasingly common. Such devices typically facilitate data communications between a source and a destination across a communications medium such as a telephone line, coaxial cable, twisted pair cabling, copper wires, fiber optics, radio frequency (RF), infrared or other wireless interface, or the like. Generally, such communications are bi-directional in that both source and destination are allowed to transmit and receive data over the same medium.
With reference to
FIG. 1
, a conventional communications system
100
includes a communications device
102
(such as a modem) that handles transmit data
112
and receive data
114
on a communications medium
104
(such as a telephone line). Typically, transmit data
112
is provided to the medium
104
via a line driver
150
. Line driver
150
is commonly represented as an amplifier
106
and an output impedance Z
LD
(represented in
FIG. 1
as resistor
108
). Receive data
114
may be provided from medium
104
to communications device
102
via, for example, a separate data path
1
10
that bypasses amplifier
106
.
Generally speaking, it is desirable to match the total output impedance of the line driver to the impedance of communications medium
104
(represented in
FIG. 1
as Z
line
). The total output of the impedance may be represented as the series of the line driver output impedance (which is usually quite low, such as on the order of a few milli-ohms) with line driver impedance Z
LD
. Communications medium
104
typically exhibits a relatively low impedance (e.g. on the order of 100 ohms), so Z
LD
may be designed to be correspondingly low (e.g. on the order of 100 ohms, or as otherwise appropriate) when the line driver is activated. Failure to at least approximately match Z
LD
to Z
line
could result in undesirable reflections in medium
104
, thus resulting in unwanted noise.
Further, it is generally desirable to conserve power in line driver
150
whenever possible. One technique for reducing overall power consumption involves powering down line driver
150
when device
102
is not transmitting on medium
104
. For reasons that will become apparent, it has been generally difficult to power down line driver
150
without affecting impedance Z
LD
. Hence, the driver impedance Z
LD
of many prior art systems did not adequately match the impedance Z
line
of communications medium
104
during power-down mode even if the impedance's properly matched when the line driver was powered up.
It is therefore desirable to create a line driver that provides adequate impedance matching with the communications line during all modes of operation while reducing overall power consumption.
BRIEF DESCRIPTION OF EXEMPLARY EMBODIMENTS
Various exemplary aspects of the present invention provide methods and apparatus for powering down the line driver to a state that reduces voltage drop without affecting the overall impedance of the line driver. More particularly, a power down state for line drivers and the like is suitably provided that saves power when no transmission is required. The power down mode suitably provides line termination for received data. According to various aspects of an exemplary embodiment, output devices are configured at power down such that a low impedance is maintained.
REFERENCES:
patent: 4855623 (1989-08-01), Flaherty
patent: 4961010 (1990-10-01), Davis
patent: 5321319 (1994-06-01), Mahmood
patent: 5367645 (1994-11-01), Lubeck et al.
patent: 5434519 (1995-07-01), Trinh et al.
patent: 6072333 (2000-06-01), Tsukagoshi et al.
Bazzani Cristiano
Cops Wim F.
Shamlou Daryash “Danny”
Conexant Systems Inc.
Farjami & Farjami LLP
Tran Toan
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