HC4GX15 Datasheet, PDF (318/668 Pages) Altera Corporation – HardCopy IV Device Handbook

1–54
Chapter 1: HardCopy IV GX Transceiver Architecture
Transmitter Channel Datapath
Figure 1–42. V_OD (Differential) Signal Level
Single-Ended Waveform
V_A
+- V_OD
V_B
V_OD (Differential)
= V_A – V_B
Differential Waveform
+V_OD
V_OD (Differential)
+700
0-V Differential
-V_OD
-700
Table 1–10 shows the V_OD values for different termination resistor settings.
Table 1–10. Programmable V_OD Differential Peak-to-Peak (mV) (Note 1)
Values Shown in the ALTGX
MegaWizard Plug-In Manager
85 Ω
100 Ω
0
170
200
1
340
400
2
510
600
3
595
700
4
680
800
5
765
900
6
850
1000
7
1020
1200
Note to Table 1–10:
(1) These values are preliminary.
120 Ω
240
480
720
840
960
1080
1200
—
150 Ω
Unit
300
mV
600
mV
900
mV
1050
mV
1200
mV
1350
mV
—
mV
—
mV
Programmable Pre-Emphasis
The programmable pre-emphasis module in each transmit buffer boosts high
frequencies in the transmit data signal, which might be attenuated in the transmission
media. Using pre-emphasis can maximize the data eye opening at the far-end receiver.
The transmission line’s transfer function can be represented in the frequency domain
as a low-pass filter. Any frequency components below –3dB can pass through with
minimal loss. Frequency components greater than –3dB are attenuated. This variation
in frequency response yields data-dependent jitter and other inter-symbol
interference (ISI) effects. By applying pre-emphasis, the high-frequency components
are boosted; that is, pre-emphasized. Pre-emphasis equalizes the frequency response
at the receiver so the difference between the low-frequency and high-frequency
components is reduced, which minimizes the ISI effects from the transmission
medium. Pre-emphasis requirements increase as data rates through legacy backplanes
increase. You set the pre-emphasis settings in the ALTGX MegaWizard Plug-In
Manager. The HardCopy IV GX transceiver provides three pre-emphasis taps:
pre-tap, 1st post-tap, and 2nd post-tap. The ALTGX MegaWizard Plug-In Manager
provides options to select the different values on these three taps. The pre-tap sets the
HardCopy IV Device Handbook Volume 3
© June 2009 Altera Corporation