Virtex-II Platform FPGAs: DC and Switching Characteristics
R
DS031-3 (v3.5) November 5, 2007
Module 3 of 4
Product Specification
18
Output Delay Measurements
Output delays are measured using a Tektronix P6245
TDS500/600 probe (< 1 pF) across approximately 4" of FR4
microstrip trace. Standard termination was used for all test-
The propagation delay of the 4" trace is characterized sep-
arately and subtracted from the final measurement, and is
therefore not included in the generalized test setup shown in
Measurements and test conditions are reflected in the IBIS
models except where the IBIS format precludes it. (IBIS
.) Parameters VREF, RREF,
CREF, and VMEAS fully describe the test conditions for each
I/O standard. The most accurate prediction of propagation
delay in any given application can be obtained through IBIS
simulation, using the following method:
1.
Simulate the output driver of choice into the generalized
2.
Record the time to VMEAS.
3.
Simulate the output driver of choice into the actual PCB
trace and load, using the appropriate IBIS model or
capacitance value to represent the load.
4.
Record the time to VMEAS.
5.
Compare the results of steps
2 and
4. The increase or
decrease in delay should be added to or subtracted
from the I/O Output Standard Adjustment value
(Table 17) to yield the actual worst-case propagation
delay (clock-to-input) of the PCB trace.
Figure 1: Generalized Test Setup
VREF
RREF
VMEAS
(voltage level at which
delay measurement is taken)
CREF
(probe capacitance)
FPGA Output
ds083-3_06a_092503
Table 19: Output Delay Measurement Methodology
Description
IOSTANDARD
Attribute
RREF
(
Ω)
CREF(1)
(pF)
VMEAS
(V)
VREF
(V)
LVTTL (Low-Voltage Transistor-Transistor Logic)
LVTTL (all)
1M
0
1.4
0
LVCMOS (Low-Voltage CMOS ), 3.3V
LVCMOS33
1M
0
1.65
0
LVCMOS, 2.5V
LVCMOS25
1M
0
1.25
0
LVCMOS, 1.8V
LVCMOS18
1M
0
0.9
0
LVCMOS, 1.5V
LVCMOS15
1M
0
0.75
0
PCI (Peripheral Component Interface), 33 MHz, 3.3V
PCI33_3 (rising edge)
25
10(2)
0.94
0
PCI33_3 (falling edge)
25
10(2)
2.03
3.3
PCI, 66 MHz, 3.3V
PCI66_3 (rising edge)
25
10(2)
0.94
0
PCI66_3 (falling edge)
25
10(2)
2.03
3.3
PCI-X, 133 MHz, 3.3V
PCIX (rising edge)
25
10(3)
0.94
PCIX (falling edge
25
10(3)
2.03
3.3
GTL (Gunning Transceiver Logic)
GTL
25
0
0.8
1.2
GTL Plus
GTLP
25
0
1.0
1.5
HSTL (High-Speed Transceiver Logic), Class I
HSTL_I
50
0
VREF
0.75
HSTL, Class II
HSTL_II
25
0
VREF
0.75
HSTL, Class III
HSTL_III
50
0
0.9
1.5
HSTL, Class IV
HSTL_IV
25
0
0.9
1.5
HSTL, Class I, 1.8V
HSTL_I_18
50
0
VREF
0.9
HSTL, Class II, 1.8V
HSTL_II_18
25
0
VREF
0.9
HSTL, Class III, 1.8V
HSTL_III_18
50
0
1.1
1.8
HSTL, Class IV, 1.8V
HSTL_IV_18
25
0
1.1
1.8