capabilities. Conexant’s interactive TV decoders offer CPU and

graphics performance ideally suited for such mid-range interactive

TV set top boxes, in which a system can be implemented using

8 MB or 16 MB of SDRAM, depending on the functionality desired.

Conexant’s powerful video/graphics display compositing engine

supports up to six independent image planes to enable the

rich visual interface required for simultaneous TV viewing and

application interaction. In addition, Conexant’s 2D graphics

rendering engine can composite an unlimited number of graphics

planes with transparency into a single displayable OSD plane.

More advanced interactive systems on high-bandwidth cable

networks go even further. They offer full Internet access,

including Web browsing, e-mail and chat applications.

Conexant’s architecture scales up to satisfy the requirements of

this computer-centric set top box model with a high-performance,

133 MHz, 32-bit SDRAM memory controller and a 160 MHz,

32-bit CPU providing 160 MIPS dedicated to OS and

application execution.

A high-performance 2D graphics rendering engine accelerates

8/16/32bpp graphics screen updates to support multiple

overlapping graphics screen surfaces. The display-compositing

engine enables picture-in-graphics, flicker filtering, alpha

blending and other effects. The CX22490 supports direct

attachment to an IDE hard disk drive for video pause and

Web-browser caching applications.

What is an Interactive TV Decoder?

An interactive TV decoder is a device that enables a

set top box connected to a digital TV network, to deliver

both digital TV programming and information services to a

TV set. The basic functions performed by an interactive TV

decoder include identifying and filtering specific programs

embedded in a compressed digital TV data stream, and

decompressing the video and audio data associated with

the selected program. This generates the TV program’s

picture and sound. An interactive TV decoder can also

identify and filter information sent in the digital TV data

stream. Data pertaining to interactive applications is

processed by the interactive TV decoder’s embedded CPU

under OS control, and generates a graphical user interface

that can be navigated using the set top box’s remote

control unit.

The interactive TV decoder’s graphics-controller function

allows both the TV picture and application user interface

graphics to be presented as a single image on the TV, using

a variety of video/graphics image scaling, filtering and

blending techniques. The interactive TV decoder must also

provide a return channel data communications mechanism

to allow the application to interact with the broadcast data

source. This is typically done via a telco or cable modem.

Finally, the interactive TV decoder should be able to

decrypt TV program and application content which has

been encrypted by the service provider to protect against

unauthorized access to services. Support for this kind

of conditional-access system is usually implemented via

smart card technology, combined with an embedded

decryption circuit.