Virtex-II Platform FPGAs: DC and Switching Characteristics
R
DS031-3 (v3.5) November 5, 2007
Module 3 of 4
Product Specification
41
Source Synchronous Timing Budgets
develop system-specific timing budgets. The following analysis provides information necessary for determining Virtex-II
contributions to an overall system timing analysis; no assumptions are made about the effects of Inter-Symbol Interference
or PCB skew.
Virtex-II Transmitter Data-Valid Window (TX)
TX is the minimum aggregate valid data period for a
source-synchronous data bus at the pins of the device and
is calculated as follows:
TX = Data Period - [Jitter(1) + Duty Cycle Distortion(2) +
TCKSKEW(3) + TPKGSKEW(4)]
Notes:
1.
Jitter values and accumulation methodology to be provided in
a future release of this document. The absolute period jitter
particular DCM output clock used to clock the IOB FF can be
used for a best case analysis.
2.
This value depends on the clocking methodology used. See
3.
This value represents the worst-case clock-tree skew
observable between sequential I/O elements. Significantly
less clock-tree skew exists for I/O registers that are close to
each other and fed by the same or adjacent clock-tree
branches. Use the Xilinx FPGA_Editor and Timing Analyzer
tools to evaluate clock skew specific to your application.
4.
These values represent the worst-case skew between any two
balls of the package: shortest flight time to longest flight time
from Pad to Ball.
Virtex-II Receiver Data-Valid Window (RX)
RX is the required minimum aggregate valid data period for
a source-synchronous data bus at the pins of the device
and is calculated as follows:
RX = [TSAMP(1) + TCKSKEW(2) + TPKGSKEW(3) ]
Notes:
1.
This parameter indicates the total sampling error of Virtex-II
DDR input registers across voltage, temperature, and process.
The characterization methodology uses the DCM to capture
the DDR input registers’ edges of operation. These
measurements include:
-
CLK0 and CLK180 DCM jitter in a quiet system
-
Worst-case duty-cycle distortion
-
DCM accuracy (phase offset)
-
DCM phase shift resolution.
These measurements do not include package or clock tree
skew.
2.
This value represents the worst-case clock-tree skew
observable between sequential I/O elements. Significantly
less clock-tree skew exists for I/O registers that are close to
each other and fed by the same or adjacent clock-tree
branches. Use the Xilinx FPGA_Editor and Timing Analyzer
tools to evaluate clock skew specific to your application.
3.
These values represent the worst-case skew between any two
balls of the package: shortest flight time to longest flight time
from Pad to Ball.
Revision History
This section records the change history for this module of the data sheet.
Date
Version
Revision
11/07/00
1.0
Early access draft.
12/06/00
1.1
Initial release.
01/15/01
1.2
01/25/01
1.3
The data sheet was divided into four modules (per the current style standard).
Table 18, “Delay Measurement Methodology”
04/23/01
1.5
Skipped v1.4 to sync with other modules. Reverted to traditional double-column format.