Consumer high-definition television (HDTV) and PC video applications will benefit from the industry's first triple digital-to-analog converters (DACs) that produce the complete range of analog component video and PC graphics (VESA) formats. The new THS8135/36 triple DACs announced today from Texas Instruments (TI) feature higher sampling speeds and lower power consumption than previous versions. Furthermore, the new triple DACs enable video electronics to add high-resolution PC graphics output, next to component and composite video output.

The 10-bit THS8135 and 8-bit THS8136 Video Triple DACs can be software-configured to generate standard 700mV component video output from either ITU-R.BT601 (SDTV) or SMPTE274M/296M (HDTV) YCbCr sampled signals, as well as from RGB sampled (VESA) PC graphics signals. Next to support for both color spaces (YCbCr vs. RGB), the devices include an optional scaling/clipping function on the digital input to support either full-range sampled or reduced-range (ITU-R.BT601) sampled signals. Reduced-range sampling is common in video applications to preserve headroom for overshoot/undershoot from digital video filtering. The clipping function reduces such filtering artifacts in the resulting analog signal and the input code scaling guarantees compliant analog output ranges for both PC graphics and SDTV/HDTV component video, with no need for any board hardware changes when switching between PC and video modes.

The device also includes a 'generic DAC mode'. This allows THS8135/36 to work with an external composite (NTSC/PAL/SECAM) video encoder that produces digital composite video -e.g. generated from IP embedded in an ASIC or FPGA - for final D/A conversion of the signal. The THS8135/36 can be software-switched from a 700mVpp component DAC mode to a 1.3Vpp compliant DAC mode, as required for composite video.

The new DACs also offer channel-matching specifications resulting in greater accuracy of video color and white-balance control. The devices feature a sampling speed of 240 megahertz (MHz), supporting PC display formats up to UXGA (1600x1200) resolution. This node also covers the required speed for all 18 ATSC formats for DTV, including the highest HDTV production format of 1920x1440 pixels at 60Hz. Furthermore, it is the first 10-bit triple video DAC at this speednode to be implemented in a 1.8V process.

"TI's new THS8135/36 DACs address the convergence of consumer-video and PC-graphics, offering versatility, improved quality and low power consumption for a new generation of multifunctional video applications," said Bart DeCanne, Digital Video Marketing Manager for TI. "The new solutions are the next step in TI's continuing strategy of supplying flexible solutions that enable our customers to convert a wide range of video formats from digital into a real-world analog signal."

The speed of the new THS8135/36 DACs permits video oversampling for SDTV and HDTV, relaxing the complexity and cost of analog reconstruction filtering behind the DAC, thus lowering total system cost. Other integrated functions include bi-level and tri-level sync insertion and configurable blanking for both RGB and YCrCb component inputs, as well as support for 4:4:4 and 4:2:2 sampling formats.

The THS 8135/36 isn't the first or the only triple DAC on the market. It isn't even the first such product from Texas Instruments. It is the follow-up to the THS8133/34 DAC introduced by TI and reviewed by ChipCenter in March of 1999. The THS 8135/36 offers 10-bit and 8-bit resolution respectively, but it now offers a speed upgrade from 80 mega samples per second (MSPS) to 240 MSPS in a pin compatible part. However, TI looked to the future with this version by offering it in the more advanced 0.18-micron design feature size with a 1.8V digital power supply and 3.3V analog power supply.

The THS8135 and 8136 DACs now have 1.3V output compliance for the composite video outputs. The units can switch between component outputs from 700mV to 1.3V. The DACs are a rarity because they provide access to both RGB and YCbCr (digital) signal interface types. The typical triple DAC can use either the RGB or the YCbCr interface but not both, and they don't have a configurable blanking on the output.

If you work with HDTV then you need this DAC's tri-level sync capability. The tri-level sync is important because you don't need separate circuitry to insert the sync onto the analog outputs - the DAC does it for you.

In full-scale modes, the DAC is driven to the desired video level. In reduced scale ITU-R.BT601 modes, on each of the three channels the same analog output compliance, as in full-scale mode, is reached when the DAC is driven with digital inputs within the required input code range. Note that the code range is unequal between RGBY on one hand and CbCr on the other hand in ITU-R.BT601 mode. Not only is the positioning of the blanking level different between both modes, the device also automatically compensates so the same full-scale video range is reached, based on the reduced input code range. If codes outside this range are supplied, they are clipped inside the DAC to the respective minimum/maximum value for the corresponding color component.

Set-top box makers and companies making devices that output high definition video, such as PC graphics, will appreciate the 240 MSPS because that sampling rate covers 95% of all UXGA applications

The 10-bit THS8135 Triple Video DAC is now sampling with volume production of both the THS8135 and THS8136 scheduled for the third quarter of 2001. An evaluation module (EVM) is scheduled for availability at the time of volume production.