Question about connect condition of DS80PCI402.

Hi Satoshi-san,

We do not have a manual for this specific setup condition. However, we do have some general guidelines for effective repeater placement on the signal path.

- Typically we recommend that there is at least 3-5 dB of attenuation loss after the repeater output, before reaching the target device. Placing the repeater too close to the endpoint receiver can result in the receiver having trouble resolving the incoming signal that may be subtly distorted by the repeater output driver.

- For unidirectional devices (such as the DS80PCI800), we recommend placing the repeater with about 2/3 of the attenuation loss before the repeater's input, and 1/3 of the attenuation loss after the repeater's output. For bidirectional devices such as the DS80PCI402, we recommend placing the device approximately halfway between the endpoints so that the DS80PCI402 output drivers are not overly stressed by large attenuation losses in a single direction.

From your block diagram, there seems to be very short traces on the board itself. FR-4 loss is approximately ~0.8 dB/in. (0.0315 dB/mm), so as a rough estimate, I assume:

PLX <=> 2.2 dB <=> DS80PCI402 <=> 1.6 dB <=> Connector Loss <=> Cable (2m ~8-10 dB) <=> Connector Loss <=> 1.3 dB <=> DS80PCI402 <=> 3.8 dB <=> Connector Loss <=> Target Device 

If this estimate is reasonable and connector losses are ~0.5 dB, the overall loss from PLX to target device is on the range of ~20 dB. I believe using two unidirectional devices (2 x DS80PCI800) may be more suitable, where the DS80PCI800 input is receiving a long distance of trace (~16-17 dB) and the DS80PCI800 output is driving a short distance of trace (~3-5 dB). This may work better because our the repeater CTLE is preferred over output de-emphasis for resolving a large amount of attenuation loss. In other words, the repeaters are able to recover input attenuation loss much more effectively than compensate for output attenuation loss.

Another reason for using 2 unidirectional DS80PCI800 devices is related to your second question about two DS80PCI402 devices cascaded. We do not recommend cascading 2 x DS80PCI402s on the same signal path. The repeater input CTLE gain stages and output driver adds some residual gain and output distortion to the datapath signal (in addition to recovering attenuated signal). Adding a second repeater on the same signal path may cause amplification of any unintended distortion caused by the first repeater.

Thanks,

Michael