Datasheet

7–222
For those devices (ABT16952 and ABT16500A) that have registers, the data path chosen for each device was the path that
put the device in a transparent mode. Also, for the bidirectional devices (ABT16245, ABT16952, and ABT16500A), the
A-to-B direction was used.
1
2
3
16
t
PLH14
t
PLH3
Figure 1. Skew = |t
PLH14
– t
PLH3
|
Sources of Error in Data
The data in this report was taken on an IMPACT tester, which is automatic test equipment used to characterize integrated
circuits. The tester is offset using a golden unit that has had data taken on a laboratory bench setup. The offsetting process is
the main source of error in the data.
Briefly, the tester is offset in the following manner. The golden unit has its propagation delay measurements taken at 25°C and
85°C using a pulse generator as the source and an oscilloscope as the measurement device. The golden unit is then placed on
the IMPACT and the data is again taken. The difference between the two values is the offset. The 25°C offsets are used for
the data taken at –55°C, –40°C, and 25°C, while the 85°C offsets are used at 85°C and 125°C.
Great care is taken during this process to ensure that the induced error is kept to a minimum. For example, the boards are
checked before use to ensure the output loads are correct, the oscilloscope is calibrated each day, and the input signals are
closely monitored to ensure that the intended signal is delivered to the golden unit.
This reduction in error is quite important in this application because the average skews for the devices are about 200 ps. A 20-ps
error in offsets translates into an approximate error of 10% in the output skew data. However, it can be seen in the curves
presented here that the error has been kept to a minimum and that the curves are fairly well behaved.
Summary
The family of curves presented in Figures 2 through 9 demonstrates that the Texas Instruments Advanced BiCMOS family
of devices can be expected to produce an average skew between outputs that remain below 400 ps for devices with single
switching outputs. Also, when a device’s outputs switch simultaneously, the average skew across the outputs can be expected
to remain below 700 ps.