Vitesse VSC8221 Ethernet PHY for Media Converter Application

Question

I'm currently designing a media converter board using Vitesse VSC8221. Just as an FYI, the documents for this product are all available at the product page. No NDA is required.

When I say media converter, I actually meant SFP interface for fiber medium to RJ45-CAT5 for copper medium, and vice versa.

Now, I've studied the datasheet and application notes of the chip quite extensively, and the chip does offer a 'Media Converter' mode (Datasheet:Section 4.2:Page 2). The application diagram for this mode is as shown below.

While I can use this mode, one drawback of this mode is that it only supports 1000BASE-T to 1000BASE-X. It doesn't support conversion to/from 10/100BASE-TX.

But in the datasheet, it's also showing a mode where it supports all 10/100/1000BASE-T to GBIC/SFP interface. The application diagram is as shown below.

Now, my questions are: Can I use the second mode to do my media conversion? I know there are copper SFP also, but since the interface is specified as SFP, what's stopping me from using an optical transceiver SFP? If the Fiber-SFP(eg to MAC) can transfer data both ways, why can't I simply put my optical module at the SFP signal pins and get it to work as optical-copper converter instead?

If no, does this chip allow me to do a one-chip media conversion that supports all 10/100/1000BASE-T, even if that means I can't use the 'Media Converter' mode? I've read the datasheet and I'm still not sure of the answer.

I hope someone can offer some advice on the matter. Thank you so much in advance.

Answer 1

The IC you mentioned (Vitesse VSC8221) is a typical 10/100/1000BASE-T/TX/T PHY with a 1000BASE-X/SGMII interface to the MAC. It is intended to design SFP modules, not to design media converters.

As i see you try to design a converter for 10/100/1000 Mbps copper to/from 1000 Mbps fiber optic. If it is so, you should use a switch instead of simple PHYs, because you need a speed matching mechanism (packet buffering memory) as the basis for "store-and-forward" concept.

The PHY you selected has no packet buffering memory and works like a "pass-thru" block: speeds on both its sides must be equal. It also does not manage CDMA/CD to deal with half duplex connections itself. It's only PHY and it needs a MAC over it.

Search for appropriate 2-port switch IC (often called "converter") with integrated PHYs (one is 10/100/1000 copper and one is 1000BASE-X serdes for fiber optic) for your task. Good luck.

Answer 2

I do the same project like you.

I searched a tons of webpages for the Fiber-ethernet converter ideas. The answer is: YES, you can, BUT (always a "but" there) beware.

Not only Visette, other company offer you a way to design the converter module, like here at Avago products

Idea here is : You get a Transceiver that give you an output for Ethernet standard, use an PHY chip to execute the information and transfer it to RJ-45 port. transceiver here is : AFBR-5972Z. PHY chip is : IP113A-LF Good: you can make for your demo Bad : it only transmit in the range from 50m to maximum 70m

same with Texas Instrument, T.I also support the schematic design for converter board with TI PHY chip and fiber Transceiver from Avago. But, this board can support you to transmit over 2km

Some company have the final board for you to combine with your system such as MPL company with board TX2FX

Vitesse can help you too, it easier than above cause it connected directly with SFP cage.

BUT, the problem is: Transceiver module is very expensive compare to the final products from other company. Actually, the module cost you about 20 - 45$, and the PHY chip cost you about 5 - 10$. At, final board, you will cost about 60 - 75$. In fact, some fiber-ethernet converter box can be bought with only 16$ (included shipping cost)

But, wait a second. There is a hope for you. Some guys use Avago HFBR-14xxZ and HFBR-24xxZ to be a fiber transceiver to embedded into board with PHY chip. It's cheaper than above, but at my point of view, it's still expensive.

If you must defense your project, you should take your point of view about the process to make the board, cost, and the flexibility.

Wish you have a good luck.