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JoeS37
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"C" does not stand for Camera
JoeS37   9/2/2014 12:25:12 PM
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And if it did, what would "M" in M-phy stand for?

Truth is, these letters are related to symbol rates in MHz - they are Roman numerals!.

D = 500.  the first D-PHY spec in 2009 said HS speed was intended to be 80 to 1000Mb/s. The upper limit has since been raised.

M = 1000. The first HS Gear was 1.248Gb/s (HS-G1A) or 1.4576Gb/s (HS-G1B).  Later specs added HS-G2 and HS-G3  (and stay tuned for HS-G4).

C = 100.  C-PHY is derived from D-PHY (except it doesn't forward a clock, it is embedded) but since it transfers 2.28 bits per symbol the symbol rate for the same data transmission rate can be less than half as much as D-PHY would need.  According to the latest draft C-PHY spec it is "intended to define a solution for a symbol rate range of 80 to 2500 Msps per lane, which is the equivalent of about 182.8 to 5714 Mbps per lane."

It is interesting to note that C-PHY balances the current in 3 wires, does not need an extra pair of wires for clock, and achieves speeds up to M-PHY's HS-G3 but at a symbol rate 1/2.28 of M-PHY's bit rate.  It reuses D-PHY's low speed mode ... I think in some cases C-PHY could be viewed as a substantial improvement over real D-PHY.

Chris.Loberg
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Re: "C" does not stand for Camera
Chris.Loberg   9/2/2014 3:14:33 PM
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Thank you Joe. For clarifying the "C" in CPHY. I was guessing on the naming convention given the heavy focus on CSI/DSI support in this revision to DPHY. I agree with you that CPHY offers great promise to increasing DPHY throughput without hanging more symbol-based overhead on.

steveiol
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C does not stand for 100
steveiol   1/15/2016 11:11:55 AM
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C-PHY took a departure from the D-PHY and M-PHY naming convention. The C doesn't stand for "100 mbps", it stands for "channel limited". As in, it can run over lower quality interconnects (at least compared to what D-PHY or M-PHY would require). This presumably makes it cheaper to implement.



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As data rates begin to move beyond 25 Gbps channels, new problems arise. Getting to 50 Gbps channels might not be possible with the traditional NRZ (2-level) signaling. PAM4 lets data rates double with only a small increase in channel bandwidth by sending two bits per symbol. But, it brings new measurement and analysis problems. Signal integrity sage Ransom Stephens will explain how PAM4 differs from NRZ and what to expect in design, measurement, and signal analysis.

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