Datasheet

Spartan-7 FPGAs Data Sheet: DC and AC Switching Characteristics
DS189 (v1.2) June 20, 2017 www.xilinx.com
Preliminary Product Specification 19
Output Delay Measurements
Output delays are measured with short output traces. Standard termination was used for all testing. The
propagation delay of the trace is characterized separately and subtracted from the final measurement, and
is therefore not included in the generalized test setups shown in Figure 1 and Figure 2.
Parameters V
REF
, R
REF
, C
REF
, and V
MEAS
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 this method:
1. Simulate the output driver of choice into the generalized test setup using values from Table 20.
2. Record the time to V
MEAS
.
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 V
MEAS
.
5. Compare the results of step 2 and step 4. The increase or decrease in delay yields the actual
propagation delay of the PCB trace.
X-Ref Target - Figure 1
Figure 1: Single-ended Test Setup
X-Ref Target - Figure 2
Figure 2: Differential Test Setup
V
REF
R
REF
V
MEAS
(voltage level when taking delay measurement)
C
REF
(probe capacitance)
Output
X16654-092616
R
REF
V
MEAS
+
–
C
REF
Output
X16640-092616