Triple Skew-Compensating Video Delay Line with Analog and Digital Control

The AD8120 is a triple broadband skew delay compensation IC that corrects for time mismatch of video signals incurred by transmission in unshielded twisted pairs of Category-5 and Category-6 type cables. Skew between the individual pairs exists in most types of multi-pair UTP cables due to the different twist-rates used for each pair in order to minimize crosstalk among the pairs. Some pairs are therefore longer than others, and in long cables, the difference in propagation time between two pairs can be well into the tens of nanoseconds.

The AD8120 contains three delay paths which provide broadband delays up to 50 nanoseconds, in 0.8 ns increments, using 64 digital control steps or analog control adjustment. The delay technique used in the AD8120 minimizes noise and offset at the outputs. It has a broad bandwidth that ranges between 106 MHz and 152 MHz, depending upon the delay setting. This high output bandwidth capability makes AD8120 ideal in applications that receive high-resolution video over UTP cables.

The logic circuitry inside the AD8120 provides for individual delay control of each path. The three delay times can be independently set using a standard four-wire SPI bus, standard I2C bus or by applying three analog control voltages to the VCR, VCG, and VCB pins. Analog control offers a simple solution for systems that do not have digital control available, the simplest being potentiometer control.

The AD8120 is designed to be used with the AD8123 triple UTP equalizer in video-over-UTP applications, but can be used in other applications where similar controllable broadband delays are required.

The AD8120 is available in a 5 mm × 5 mm 32-lead LFCSP package and is rated to operate over the industrial temperature range of -40°C to +85°C.

Applications

* Keyboard-video-mouse (KVM)

* Digital signage

* RGB video over UTP cable

* Professional video projection and distribution

* HD video

* Security video

* General broadband delay lines

Data Sheet, Rev PrA, 10/2008

* Corrects for unshielded twisted pair (UTP) cable delay skew * Delay of up to 50 ns per channel * High speed

200 MHz BW @ VOUT = 1.4 V p-p and 0 ns delay

150 MHz BW @ VOUT = 1.4 V p-p and 50 ns delay * Excellent channel-to-channel matching

30 mV offset matching RTI

0.8% gain matching