Hi Cortex, I checked over the numbers and methodology and they are correct. At first glance it appears wrong to have minimum transmit amplitude the same for a long cable as a short one. Let me explain. The frequencies are in the microwave region and so the amplitudes are not directly observable. That is, the signals when connected in system are not the same (mismatch) as when a transmitter is connected to a matched load, and when a probe is connected the system is significantly changed (loading). This situation is a consequence of the physics. The next question to ask is: what do these specifications mean? Some specifications refer to amplitude that exists while connected in system. Although it is possible to infer amplitude while connected in system, it requires characterization of the paths and complex calculations. Amplitude while connected in system places a great burden on the test engineer, especially if he is required to show and quantify accuracy. The SATA spec covers amplitude seen while driving a matched load. So it is directly observable. The accuracy of this type of measurement can be quantified by knowing instrument accuracy and match, and the test adapter characteristics. Thus, systematic errors (or bias) in the measurements can be removed. The Gen1i/2i specs have transmitters driving a matched load; the SATA cable is not part of this measurement. The interconnect can be a 1 meter cable, or no cable at all. Comparing the Gen1i/2i transmit and receive amplitudes should be consistent with this. The Gen1x/2x specs have transmitters driving a matched load (the zero length case) and driving through a TCTF (compliance channel). The requirement for transmitters is the amplitude should be within spec with zero length and with a TCTF connected without any changes to the transmitter settings. The Gen2x spec is setup to be compatible with SAS. In real cases, the output match from the interconnect is an important parameter to the amplitude at a receiver. The absence of output match from the TCTF definition and the lack of dealing with the impedance match issue in system are weaknesses in this spec. So if a Gen2x transmitter and TCTF delivers 400mVdpp into a matched load, AND if the same transmitter without TCTF delivers greater than 400mVdpp and less than 1600mVdpp, then it is within spec if both conditions are met. Specifications aren't of much use unless they can be tested. The harder it is to test against a spec, the fewer devices will be tested, and the effectiveness in ensuring quality suffers. That's the advantage in specing quantities observable in test setups. It's practical. Regards, Chuck Hill SATAIO Phy group chair -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Cortex.Chen@xxxxxxxxxxxx Sent: Wednesday, February 22, 2006 0:08 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] SATA II Electrical Specification Dear Experts, Recently I read the SATA spec, the min differential output voltage is defined 400mV for all Gen1 & Gen2 types (i/m/x) that shocks me. It means that trace length should be as short as possible for current project and long backplane is not long (interconnect loss budget is changed from 9.275dB to 3.255 dB for 2x). Who can tell me the story/history of the electrical specification? Note 1: <Serial ATA II: Electrical Specification, rev. 1.0, page 44 & 47> 1i 1m 1x 2i 2m 2x Min TX 400 500 800 400 500 800 mV Min RX 325 240 275 275 240 275 mV <Serial ATA Revision 2.5, page 135 & 138> 1i 1m 1x 2i 2m 2x Min TX 400 400 400 400 400 400 mV Min RX 325 240 275 275 240 275 mV Note 2: i: PC motherboard to device application m: Short backplane and external desktop application x: Long backplane and system-to-system application Sincerely Cortex Chen ³¯¥ÃªN SI Section, ESBU Quanta Computer Inc. No. 211, Wen Hwa 2nd., Kuei Shan Hsiang, Tao Yuan Shien, Taiwan. 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