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serial codec/serdes chips

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Marko

Fri Feb 08 2013, 10:10PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi guys

I'm looking for a chip that could be transparently used for communication over a duplex fiber optic link, which has LVDS I/O .
I need to take either parallel or serial data with a clock signal, convert it to a suitable protocol and send it over the LVDS to the fiber optic modules. This means the chips have to perform differential manchester or whatever encoding within them and output signals suitable for 2-wire LVDS transmission.

The parallel input to the chip would also ideally be 8 bit bidirectional bus or something like that.

I've found a lot serdes IC's but most seem to be huge, complex, with transfer rates into gigabits/s and most of them need clock signal for communication as well!

I'm really looking for something minimal, hopefully in a SSOP package with data rates of 100mbit/s or so at most.

On the other hand, I could also use a chip that converts clocked high speed serial signal to a suitable code with embedded clock information - I'm sure chps like that must exist, but not even sure of their name, serial codecs or whatever?

In any case, as you can see I'm not very experienced in the field, so anyone knowledgeable in this industry would be of great help!

P.S. I'd also prefer chips from ti if possible since they are sample-friendly, however I haven't found anything too usable yet among their parametric tables!

Marko

Pinky's Brain

Fri Feb 08 2013, 11:52PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

If you already looked at TI's chips maybe you should tell us what's wrong with ones you could find ... something like this (with the corresponding deserializer) tix almost all the boxes AFAICS. It's a minimum serial speed is 160 Mb/s, but is that really a huge problem?

Marko

Sat Feb 09 2013, 02:21PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi Pinky

Well, yes, the huge minimum data rates are actually a problem, since I'm looking to use cheap optical LAN modules like these

that only go up to 155mbit/s or so.

Very few serdes chips actually seem to have minimum data rates in this range though!

The other things that I hoped for were to get the solution within one chip (fairly rare) and bidirectional outputs (never even seen!)

The purpose of this would be to link a FT232H IC over a fiber optic link to a remote FPGA. At first I thought to simply use the available FT232 UART over some LVDS transceiver chips to interface the fiber optic modules. But, I figured It'd be really nice if I could use the connection to program the fpga, which is difficult over normal UART. I also figured it'd be much better idea to transmit a signal with embedded clock information, rather than a common UART signal at these data rates.

The problem with FT232H is that it has tri-state bidirectional output, and most serdes chips are unidirectional. The number of chips is quickly becoming rather annoying! :|

On the other hand FT232 also has clocked serial outputs, and I wondered whether there is a chip that could simply take these clocks and put out a differential signal embedded clock?

So far it looks like the best option will be 2+2 ser/des chips + some glue logic to make it work....

Marko

Pinky's Brain

Sat Feb 09 2013, 03:39PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Since you're familiar with FPGAs ... why not just use a FPGA? A small ICE40 is dirt cheap and has native LVDS (unlike cheap CPLDs where you have to mess around with external components).

Steve Conner

Sun Feb 10 2013, 10:09AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I think Anders M. used the DS90UR241 and DS90UR124 for this. They are designed for embedded clock LVDS links for small LCD panels.

They're always going to need a clock to work. Try to think how you would do it without a clock.

Pinky, can you program the ICE40 with free software or do you need to buy something?

Pinky's Brain

Sun Feb 10 2013, 05:20PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

The software is free, about the quality I have no idea (it's a separate toolset from Lattice's normal design software, because it's a recently acquired architecture).

For IO/$ there is nothing which can compete with the ICE40 AFAICS (CPLD architectures included).

Steve Conner

Mon Feb 11 2013, 12:08PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hmm.. I'm interested in using the ICE40 to convert HDMI video to 18-bit parallel. But I don't see a HDMI decoder core for it, even though the hardware claims to support HDMI.

On the original topic, there's also the DS99R103. It goes down to 3MHz clock rate, so has a better chance of working with 155Mbit fibre optics.

Pinky's Brain

Mon Feb 11 2013, 04:11PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

The ICE40 doesn't have a SERDES (wasn't important here because even without it, it can handle 400+ Mbps) so it won't be able to generate/receive HDMI. AFAICS they only claim HDMI support for the ECP3.

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