DS125BR800 Datasheet, PDF (13/59 Pages) Texas Instruments – Low-Power 12.5-Gbps 8-Channel Repeater With Input Equalization and Output De-Emphasis

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DS125BR800
SNLS426E – AUGUST 2012 – REVISED JANUARY 2015
8.3.2 PCIe Signal Integrity
When using the DS125BR800 in PCIe Gen-3 systems, there are specific signal integrity settings to ensure signal
integrity margin. The settings were achieved with completing extensive testing. Contact your field representative
for more information regarding the testing completed to achieve these settings.
For tuning the in the downstream direction (from CPU to EP).
• EQ: use the guidelines outlined in Table 2.
• De-Emphasis: use the guidelines outlined in Table 3.
• VOD: use the guidelines outlined in Table 3.
For tuning in the upstream direction (from EP to CPU).
• EQ: use the guidelines outlined in Table 2.
• De-Emphasis:
– For trace lengths < 15" set to -3.5 dB
– For trace lengths > 15" set to -6 dB
• VOD: set to 900 mV
Level
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
EQA1
EQB1
0
0
0
0
R
R
R
R
Float
Float
Float
Float
1
1
1
1
EQA0
EQB
0
R
Float
1
0
R
Float
1
0
R
Float
1
0
R
Float
1
Table 2. Equalizer Settings
EQ – 8 bits [7:0]
0000 0000 = 0x00
0000 0001 = 0x01
0000 0010 = 0x02
0000 0011 = 0x03
0000 0111 = 0x07
0001 0101 = 0x15
0000 1011 = 0x0B
0000 1111 = 0x0F
0101 0101 = 0x55
0001 1111 = 0x1F
0010 1111 = 0x2F
0011 1111 = 0x3F
1010 1010 = 0xAA
0111 1111 = 0x7F
1011 1111 = 0xBF
1111 1111 = 0xFF
dB at
1.5 GHz
2.5
3.8
5.0
5.9
7.4
6.9
9.0
10.2
8.5
11.7
13.2
14.4
14.4
16.0
17.6
18.7
dB at
2.5 GHz
3.5
5.4
7.0
8.0
10.3
10.2
12.4
13.8
12.6
16.2
18.3
19.8
20.5
22.2
24.4
25.8
dB at
4 GHz
3.8
6.7
8.4
9.3
12.8
13.9
15.3
16.7
17.5
20.3
22.8
24.2
26.4
27.8
30.2
31.6
dB at
6 GHz
3.1
6.7
8.4
9.1
13.7
16.2
15.9
17.0
20.7
21.8
23.6
24.7
28.0
29.2
30.9
31.9
Suggested Use⁽¹⁾
FR4 < 5 inch trace
FR4 5-10 inch trace
FR4 10 inch trace
FR4 15-20 inch trace
FR4 20-30 inch trace
FR4 25-30 inch trace
FR4 25-30 inch trace
8m, 30awg cable
> 8m cable
(1) Cable and FR4 lengths are for reference only. FR4 lengths based on a 100 Ω differential stripline with 5-mil traces and 8-mil trace
separation. Optimal EQ setting should be determined via simulation and prototype verification.
Level
1
2
3
4
5
6
7
DEMA1
DEMB1
0
0
0
0
R
R
R
Table 3. Output Voltage and De-Emphasis Settings
DEMA0
DEMB0
0
R
Float
1
0
R
Float
VOD Vp-p
0.8
0.9
0.9
1.0
1.0
1.0
1.1
DEM dB⁽¹⁾
0
0
- 3.5
0
- 3.5
-6
0
Inner Amplitude
Vp-p
0.8
0.9
0.6
1.0
0.7
0.5
1.1
Suggested Use⁽²⁾
FR4 < 5 inch 4–mil trace
FR4 < 5 inch 4–mil trace
FR4 10 inch 4–mil trace
FR4 < 5 inch 4–mil trace
FR4 10 inch 4–mil trace
FR4 15 inch 4–mil trace
FR4 < 5 inch 4–mil trace
(1) The VOD output amplitude and DEM de-emphasis levels are set with the DEMA/B[1:0] pins.
The de-emphasis levels are available in PCIe Gen-3 modes when MODE = 1 (tied to VIN)
(2) FR4 lengths are for reference only. FR4 lengths based on a 100 Ω differential stripline with 5-mil traces and 8-mil trace separation.
Optimal DEM settings should be determined via simulation and prototype verification.
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