This was another great post. I hope to see you do an Ethernet chip/card post in the future. I had a couple question about the following:
>"The block diagram below shows the complex functionality of the chip. Starting in the upper right, the analog front end circuitry communicates with the ring. The analog front end extracts the clock and data from the network signals."
Do all non-optical network cards have a similar analog circuit as well? Is this generally the transceiver chip on the card?
>"The chip's logic is implemented with a CMOS standard cell library and consists of about 24,000 gates. The idea of standard-cell logic is that each function (such as a NAND gate or latch) has a standard layout."
Are these cell libraries the same as an IP block that you would license today when designing a chip? Did cell libraries become common around the time of this chip?
> Do all non-optical network cards have a similar analog circuit as well? Is this generally the transceiver chip on the card?
Even optical cards have this kind of circuitry in the PHY chip. While the SFP module usually contains surprising amount of logic, most of it has to do with configuration and testing and in the end it is just an pair of LEDs with configurable analog amplifiers.
On the other hand for modern ethernet over TP (1Gbps and up) the analog interface circuitry is significantly more complex (and power hungry), because calling the thing baseband (the "base" in "1000-base-T") somewhat stretches the definition of the word. It uses various line coding and signal processing tricks to squeeze all the bandwith out of the wire.
>"because calling the thing baseband (the "base" in "1000-base-T") somewhat stretches the definition of the word. It uses various line coding and signal processing tricks to squeeze all the bandwith out of the wire."
Interesting. Can you elaborate on why using "base" is a stretch here? I don't think I've heard this before. It's been a while since I've looked at layer 1 but isn't Ethernet just Manchester encoding? What other signal tricks are generally used?
Might you or anyone else have any good resources for Ethernet PHY circuits?
High speed on copper, for networking anyway, has gone all analog now. That's more of a 'broad'-band (in the literal sense) than 'base'-band (in the single frequency, off/on) sense.
Edit:
The Wikipedia page for broadband says it better: "The key difference is that what is typically considered a broadband signal in this sense is a signal that occupies multiple (non-masking, orthogonal) passbands, thus allowing for much higher throughput over a single medium but with additional complexity in the transmitter/receiver circuitry." -- https://en.wikipedia.org/wiki/Broadband
I haven't looked at Ethernet chips in detail, but they have similar analog circuitry. A "PHY" (physical layer) module does the analog encoding and decoding.
Standard cell libraries are lower-level than IP blocks since you're dealing with gates rather than functional units. I'm sure someone here knows about how they are licensed.
On the chip I looked at, the analog module and the CPU were treated as IP blocks. These blocks were built by IBM so the intellectual property itself wasn't an issue. But the blocks were designed by other teams and essentially dropped onto the chip unchanged. For the revised version of the chip, they redesigned the logic but kept the original analog and CPU blocks.
>"The block diagram below shows the complex functionality of the chip. Starting in the upper right, the analog front end circuitry communicates with the ring. The analog front end extracts the clock and data from the network signals."
Do all non-optical network cards have a similar analog circuit as well? Is this generally the transceiver chip on the card?
>"The chip's logic is implemented with a CMOS standard cell library and consists of about 24,000 gates. The idea of standard-cell logic is that each function (such as a NAND gate or latch) has a standard layout."
Are these cell libraries the same as an IP block that you would license today when designing a chip? Did cell libraries become common around the time of this chip?