Controlled Impedance Driver (Source Termination); Controlled Impedance Driver With Half Impedance (Source Termination) - Xilinx SelectIO 7 Series User Manual

Controlled Impedance Driver (Source Termination)

To optimize signal integrity for high-speed or high-performance applications, extra
measures are required to match the output impedance of drivers to the impedance of the
transmission lines and receivers. Optimally, drivers must have an output impedance
matching the characteristic impedance of the driven line, otherwise reflections can occur
due to discontinuities. To solve this issue, designers sometimes use external-source
series-termination resistors placed close to the pins of high-strength, low-impedance
drivers. The resistance values are chosen such that the sum of the driver's output
impedance plus the resistance of the source series-termination resistor roughly equals the
impedance of the transmission line.
DCI can provide controlled impedance output drivers to eliminate reflections without
requiring the use of an external source-termination resistor. The impedance is set by the
external reference resistors with resistance equal to the trace impedance.
The DCI I/O standards supporting the controlled impedance driver are: LVDCI_15,
LVDCI_18, HSLVDCI_15, HSLVDCI_18, HSUL_12_DCI, and DIFF_HSUL_12_DCI.
Figure 1-8
X-Ref Target - Figure 1-8

Controlled Impedance Driver with Half Impedance (Source Termination)

DCI also provides drivers with one half of the impedance of the reference resistors. This
doubling of the reference resistor value reduces the static power consumption through
these resistors by a factor of half. The DCI I/O standards supporting controlled impedance
drivers with half-impedance are LVDCI_DV2_15 and LVDCI_DV2_18.
Figure 1-9
reference resistors R must be 2 × Z
X-Ref Target - Figure 1-9
7 Series FPGAs SelectIO Resources User Guide
UG471 (v1.10) May 8, 2018
7 Series FPGA DCI—Only available in the HP I/O banks
illustrates a controlled impedance driver in a 7 series device.
R
7 Series FPGA
HP Bank DCI
Figure 1-8: Controlled Impedance Driver
illustrates a controlled driver with half impedance inside a 7 series device. The
in order to match the impedance of Z
0
R/2
7 Series FPGA
HP Bank DCI
Figure 1-9: Controlled Impedance Driver with Half Impedance
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IOB
Z
0
UG471_c1_10_101810
IOB
Z
0
UG471_c1_11_101810
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