Interfacing with Stability
Extron originally released ADSP™ (Advanced Digital Sync Processing) when the RGB 202xi interface was introduced. Due to ADSP™, the RGB 200Rxi Series have become the preferred interfaces for digital displays. Since ADSP™ cleans up and stabilizes the synchronization signals, it prevents many common image problems. Users have found that the 200Rxi series will solve almost any sync related problem. ADSP is currently found in the RGB 109xi/112xi/160xi Series/200Rxi Series/460xi Series/470xi Series/560 AKM/580xi interfaces and the SS 200 sync stabilizer.
STANDARD SYNC PROCESSING
To understand why ADSP™ makes a difference, it is necessary to understand how an interface typically accomplishes horizontal/vertical shifting and sync combining. Both of these operations are performed in many interfaces. Unfortunately, these operations change the sync in such a way that it becomes unacceptable for most digital displays.
Horizontal shift is achieved by shifting the sync signal in relation to the video signal. Figure 1 shows an example of a video signal (the red channel), with respect to the horizontal sync signal. To shift the video on the screen, it is necessary to shift the horizontal sync signal in relation to the video signal. The simplest way to do this is to delay the horizontal sync signal. Doing this will allow the image on the screen to be moved to the left. An example of delaying the sync is shown at the right of Figure 1.
Delaying the sync signal with respect to the video signal will allow shifting of the image to the left, but not to the right. Shifting the image to the right is not possible since that would require moving the sync signal in the opposite direction time-wise. This would require creating the sync pulses before they are generated by the source. In order to gain the ability to shift an image both right and left horizontally on a screen, it is necessary to delay the sync in relation to the video signal by one line of video. Using this method the sync can now be delayed or advanced in time as needed, and it is now possible to shift the image on the screen left and right.
Vertical shift (positioning) is accomplished in a manner similar to horizontal shift, except that the sync is delayed by one vertical field instead of by one line. Other than that, the same process of adjusting the sync in relation to the video signal is used.
Sync combining is another operation that will alter sync signal timing. In order to convert RGBHV into RGBS, it is necessary to combine the horizontal sync signal and vertical sync signal into one composite sync signal. This is done by using an XOR (exclusive OR) gate. The H&V signals are fed into the XOR gate and combined into a composite sync signal. This method is reliable and is used throughout the interfacing industry. However, it does change the sync timing by altering the position of the horizontal sync pulse during the vertical interval.
DIGITAL DISPLAY DEVICES AND SYNC
Digital display devices, such as LCD, DLP, and plasmas, typically need to see a sync signal that has not been processed in any way. Any change in the timing relationship between the video signal and the sync signal, or between the H&V sync will likely make the sync signals unacceptable for a digital display device. This usually results in tearing, hooking, or bending at the top of the screen. The original timing relationship that existed between the video signal and the sync signal must stay intact.
Extron's exclusive ADSP™ takes sync processing to a new level. Through an exclusive digital sync processing method, interfaces with ADSP™ can shift both vertical and horizontal sync without creating any delay. This allows the user to still use the horizontal and vertical positioning features even when using a digital display device. An interface with ADSP™ can also combine separate H and V into composite sync without altering the sync timing, like an XOR circuit. The resulting signal will be acceptable to most digital display devices. In fact, the resulting signal can be converted back into separate H&V and still be acceptable to a digital display device because the timing was never altered. Extron interface products that have ADSP™ will also correct sync that has already been altered either by horizontal or vertical shift operations or by sync combining. A sync signal that has already been altered by either operation can be fed to an Extron interface with ADSP™ and the output signal will be acceptable to a digital display device.