VSC7177 查看數據表（PDF） - Maxim Integrated

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VSC7177

Enhanced 2:1 Port Selector for Serial ATA and Serial Attached SCSI

Maxim Integrated 

VSC7177

Data Sheet

Output Amplitude and Pre-Emphasis

The output buffers each have an amplitude control input pin (HIV0, HIV1, and HIV2 corresponding to port 0, port 1,

and port 2, respectively) that sets the differential output voltage to normal Serial ATA levels. See Table 6.

Recommended output AC-coupling capacitor values are 0.01 μF. When the amplitude control pin is HIGH, the output

is configured for high voltage swing mode, which is useful for driving extended length media such as backplanes or

external cables. Setting the output to high swing mode should be done only in controlled environments because the

output voltage exceeds the Serial ATA 1.0 differential mode specifications.

The output buffers have a pre-emphasis circuit that is enabled when HIVx is HIGH. Pre-emphasis accentuates higher

frequency signals in a transmitted data stream. This feature takes into consideration that a signal loses amplitude and

affects the data eye opening as it goes through long trace length runs. Figure 5 shows the effects of the pre-emphasis

feature. The amplitude increase is between 20% and 30%, and the duration of the amplitude increase is between

150 ps and 300 ps.

Table 6. Output Amplitude and Pre-Emphasis

HIVx

0

1

Output Swing Level

Normal

HIGH

Pre-Emphasis

None

Enabled

Pre-Emphasis Disabled

Pre-Emphasis Enabled

VOUT

001 11 1 1 010

VOUT

0 01 1 1 1 1 0 1 0

Figure 5. Pre-Emphasis Diagram

11 of 24

Revision 4.2

July 29, 2005

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