The invention relates to display devices. More specifically,
the invention relates to digital display interface suitable for coupling connecting
AC coupled video sources and/ or sinks to DC coupled video sink and/or source devices.
High-speed serial interfaces transfer data at rates in
the range of one or more gigabits per second (Gbps), requiring considerable care
in the design and layout of the circuit board and often requiring AC-coupling and
differential signaling for reliable communications. In general, AC-coupled systems
allow for the migration of semiconductor process to very deep sub-micron process
and for at least this reason are anticipated to be very desirable for future technologies.
In this regard, DC-coupled systems can be considered to be legacy systems. Therefore
offering a seamless interface between the two systems will allows for the AC coupled
system to leverage the advancement of the semiconductor technology while providing
for the opportunity of backward interoperability with the legacy system.
Today's display interconnect landscape includes a number
of DC coupled interfaces such as the VGA (analog) and DVI (digital) for desktop
display interconnect applications as well as LVDS (digital) for internal connectivity
applications within laptops and other all-in-one devices. Graphics IC vendors, display
controller IC vendors, monitor manufacturers and PC OEMs as well as desktop PC consumers,
to one degree or another, must factor interface choice into their design, product
definition, manufacturing, marketing and purchase decisions. For example, if a consumer
purchases a PC with an analog VGA interface then the consumer must either purchase
an analog monitor or a digital monitor in which the analog video signal provided
by the VGA interface has been digitized by way of an inline analog to digital converter
(ADC) or an ADC built into the particular monitor.
Unfortunately, however, a VGA connector takes up a lot
of real estate on a computer and was not designed for high-definition content since
it can not handle high data rates. Even though the DVI interface supports high-definition
television it does not allow for interactive communication between devices. Therefore,
an AC coupled interface technology referred to as DisplayPort has been developed
that addresses a number of the problems associated with currently available interconnects.
For example, Display Port improves on low-voltage differential signal, or LVDS,
designs as well as provides for higher serial data rates with transfer rate of 1.62
or 2.7 gigabits per second and video signal supports 8 or 10 bit pixel format per
color channel. In order to become widely accepted, any AC coupled system (such as
DisplayPort) must be able to adapt to legacy DC coupled connections such as DVI
and HDMI (High Definition MultiMedia Interface).
Therefore, it would be desirable to provide a mechanism
for connecting DC coupled systems and AC coupled systems in a simple, easy and cost
A method of connecting an AC coupled source device to a
DC coupled receiver device by way of a connector compatible with the DC coupled
device includes generating a signal by the AC coupled source device, transmitting
the signal by the AC coupled source device, receiving the signal at a converter
unit coupled between the AC coupled source device and the connector, converting
the signal to a converted signal suitable for reception by the DC coupled receiver
device by the converter unit, passing the converted signal over the connector to
the DC coupled receiver unit, and receiving the converted signal by the DC coupled
In another embodiment, an adapter unit for providing interoperability
between an AC coupled device coupled to a DC coupled device by way of a connector
is described. The adapter unit includes a sensor for determining if the device to
which the adapter is connected is an AC coupled type device or a DC coupled type
device. If the device to which the adapter unit is connected is an AC coupled device
and a connector coupled thereto is compatible with a DC coupled device, then the
adapter unit enables a signal conditioner. In the case where the AC coupled device
is a transmitter unit, then the adapter unit conditions the signal in such a way
that is compatible with the DC coupled device. For example, if the receiver is a
DVI monitor, then the adapter conditions the incoming signal S to a conditioned
signal S' having a TDMS voltage level consistent with the DVI monitor. In the case
where the AC coupled device is a receiver unit and the connector is compatible with
the DC coupled device, then the adapter unit converts a received signal to an AC
compatible signal that is passed to the AC coupled receiver unit.
In still another embodiment of the invention, computer
program product for connecting an AC coupled source device to a DC coupled receiver
device by way of a connector compatible with the DC coupled device includes computer
code for generating a signal by the AC coupled source device, transmitting the signal
by the AC coupled source device, computer code for receiving the signal at a converter
unit coupled between the AC coupled source device and the connector, computer code
for converting the signal to a converted signal suitable for reception by the DC
coupled receiver device by the converter unit, computer code for passing the converted
signal over the connector to the DC coupled receiver unit, computer code for receiving
the converted signal by the DC coupled receiver unit and computer readable medium
for storing the computer code.
Embodiments of the invention will now be described by way
of example with reference to the accompanying drawings, in which:
- Fig. 1 shows a representative system in accordance with an embodiment of the
- Fig. 2 shows an implementation of the adapter used to connect a DC coupled transmitter
to an AC coupled receiver unit.
- Fig. 3 shows a voltage shift carried out by the adapter in accordance with an
embodiment of the invention.
- Figs. 4A and 4B show exemplary implementations of the adapter.
- Fig. 5 shows a system suitable for implementing the invention.
Reference will now be made in detail to a particular embodiment
of the invention an example of which is illustrated in the accompanying drawings.
While the invention will be described in conjunction with the particular embodiment,
it will be understood that it is not intended to limit the invention to the described
embodiment. To the contrary, it is intended to cover alternatives, modifications,
and equivalents as may be included within the spirit and scope of the invention
as defined by the appended claims.
This invention describes an adapter unit that facilitates
the interoperability of an AC-coupled system and a DC-coupled system while conforming
to the electrical specification both systems. In particular, the adapter unit includes
a sensor for determining if the device to which the adapter is connected is the
AC coupled type device or the DC coupled type device and if the connector coupled
thereto is compatible with the DC coupled device. The adapter also includes a signal
conditioner unit connected to the sensor for shifting a signal voltage of a signal
to a DC compatible signal voltage if the adapter unit receives the signal from the
AC coupled device and for shifting the signal voltage of the signal to an AC coupled
compatible signal if the adapter unit receives the signal from the DC coupled device.
Fig. 1 shows a system 100 in accordance with an embodiment
of the invention. The system 100 includes an AC coupled transmitter 102 that includes
a transmitter unit 104 coupled by way of an AC differential pair 106 to an adapter
unit 108. The adapter unit 108 is, in turn, coupled to a connector 110 compatible
with a DC coupled receiver 112 connected thereto. The DC coupled receiver 112 includes
a DC coupled receiver unit 114 coupled to the connector 110 by way of a DC differential
pair 116. Prior to the transmission of a signal S from the transmitter unit 104,
the adapter unit 108 senses the nature of the transmitter 102 (i.e., AC coupled
or DC coupled) by way of a sensor 118. The sensor 118 provides a signal 120 to a
signal conditioning unit 122 when the sensor 118 determines that the transmitter
102 is an AC coupled type device. In this situation, the signal conditioning unit
122 converts the signal S to a signal S' having a voltage level consistent with
the electrical specification of the DC coupled receiver 112. For example, in the
case that the connector 110 is a DVI cable and the receiver unit 112 is a DVI monitor
and the video source 102 is a DisplayPort PC, then the adapter unit 108 shifts the
voltage of the signal S to the signal S' having a TDMS voltage level consistent
with the DVI monitor 112 (see Fig. 3). In this way, the adapter unit 108 provides
for interoperability between AC coupled systems and DC coupled systems by allowing
an end user to connect any form of display device (be it AC coupled or DC coupled)
with any form of video source (be it AC coupled or DC coupled) using a standard
For example, Fig. 2 shows another implementation 200 of
the adapter 108 used to connect a DC coupled transmitter 202 to an AC coupled receiver
unit 204 coupled by way of the connector 110. As with the previous example, the
adapter unit 108 conditions the signal S generated by a transmitter unit 206 to
be consistent with the electrical specifications of the AC coupled receiver unit
208. Less costly than an active converter, the adaptor 108 can be used on both ends
(Source and Sink) such that an end user of DVI device (PC or monitor) can use their
existing DVI cable. Furthermore, in the DisplayPort mode, there is no performance
degradation, no adaptor/voltage shifting and no CP transcoding required and most
importantly from a consumer viewpoint, there is no need to change or alter receptacle/plug
Figs. 4A and 4B show exemplary implementations of the adapter
108 in accordance with an embodiment of the invention.
It should be noted that in a particularly useful embodiment,
the video source and/or video display is what is referred to as dual standard. By
dual standard it is meant that the particular device (be it video source or video
sink) can be configured in such as way as to be compatible with the DVI standard
or the DisplayPort standard. In those situations where either or both of the video
source and/or video sink are dual standard, then the inventive adapter unit has
the capability of detecting the particular configuration of each and configuring
Fig. 5 illustrates a system 500 employed to implement the
invention that is only an example of a system in which the present invention can
be implemented. System 500 includes central processing unit (CPU) 510, random access
memory (RAM) 520, read only memory (ROM) 525, one or more peripherals 530, graphics
controller 560, primary storage devices 540 and 550, and digital display unit 570.
As is well known in the art, ROM acts to transfer data and instructions uni-directionally
to the CPUs 510, while RAM is used typically to transfer data and instructions in
a bidirectional manner. CPUs 510 may generally include any number of processors.
Both primary storage devices 540 and 550 may include any suitable computer-readable
media. CPUs 510 are also coupled to one or more input/output devices 590 that may
include, but are not limited to, devices such as video monitors, track balls, mice,
keyboards, microphones, touch-sensitive displays, or other well-known input devices
such as, of course, other computers. Finally, CPUs 510 optionally may be coupled
to a computer or telecommunications network, e.g., an Internet network or an intranet
network, using a network connection as shown generally at 595. With such a network
connection, it is contemplated that the CPUs 510 might receive information from
the network, or might output information to the network in the course of performing
the above-described method steps. Such information, which is often represented as
a sequence of instructions to be executed using CPUs 510, may be received from and
outputted to the network, for example, in the form of a computer data signal embodied
in a carrier wave. The above-described devices and materials will be familiar to
those of skill in the computer hardware and software arts.
Graphics controller 560 generates image data and a corresponding
reference signal, and provides both to digital display unit 570. The image data
can be generated, for example, based on pixel data received from CPU 510 or from
an external encode (not shown).
Although only a few embodiments of the present invention
have been described, it should be understood that the present invention may be embodied
in many other specific forms without departing from the the scope of the present
invention. The present examples are to be considered as illustrative and not restrictive,
and the invention is not to be limited to the details given herein, but may be modified
within the scope of the appended claims along with their full scope of equivalents.
While this invention has been described in terms of a preferred
embodiment, there are alterations, permutations, and equivalents that fall within
the scope of this invention. It should also be noted that there are many alternative
ways of implementing both the process and apparatus of the present invention. It
is therefore intended that the invention be interpreted as including all such alterations,
permutations, and equivalents as fall within the scope of the present invention,
which is defined by the appended claims.