DS89C386_16 Datasheet, PDF (6/13 Pages) Texas Instruments – Twelve Channel CMOS Differential Line Receiver

DS89C386
SNLS100C – MAY 1995 – REVISED APRIL 2013
www.ti.com
In Figure 10, VX, where X is a number, is the waveform voltage level at which the propagation delay
measurement either starts or stops. Furthermore, V1 and V2 are normally identical. The same is true for V3 and
V4. However, as mentioned before, these levels are not standardized and may vary, even with similar devices
from other companies. Also note, V_REF in Figure 3 should equal V1 and V2 in Figure 10.
The single-ended skew provides information about the pulse width distortion of the output waveform. The lower
the skew, the less the output waveform will be distorted. For best case, skew would be zero, and the output duty
cycle would be 50%, assuming the input has a 50% duty cycle.
Figure 11. (Circuit 3) – Circuit for Measuring Differential Propagation Delays
(See Figure 12)
Figure 12. Waveforms for Circuit 3 – Propagation Delay Waveforms
for Circuit 3
(see Figure 11)
For differential propagation delays, V1 may not equal V2. Furthermore, the crossing point of RI and RI*
corresponds to zero volts on the differential waveform. (See middle waveform in Figure 12.) This is true whether
V1 equals V2 or not. However, if V1 and V2 are specified voltages, then V1 and V2 are less likely to be equal to
the crossing point voltage. Thus, the differential propagation delays will not be measured from zero volts on the
differential waveform.
The differential skew also provides information about the pulse width distortion of the output waveform relative to
the differential input waveform. The higher the skew, the greater the distortion of the output waveform. Assuming
the differential input has a 50% duty cycle, the output will have a 50% duty cycle if skew equals zero and less
than a 50% duty cycle if skew is greater than zero.
Only t_SK is specified in this datasheet for the DS89C386. t_SK is measured singIe-endedly but corresponds to
differential skew. Because, for single-ended skew, when V_REF equals V1 and V2, t_PHL equals t_PHLD when t_PHLD is
measured from the crossing point.
More information can be calculated from the propagation delays. The channel to channel and device to device
skew may be calculated in addition to the types of skew mentioned previously. These parameters provide timing
performance information beneficial when designing. The channel to channel skew is calculated from the variation
in propagation delay from receiver to receiver within one package. The device to device skew is calculated from
the variation in propagation delay from one DS89C386 to another DS89C386.
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