AND8090 Datasheet, PDF (11/20 Pages) ON Semiconductor – AC Characteristics of ECL Devices

AND8090/D
Skew (Duty Cycle)
Duty cycle skew is also referred to as pulse skew. Duty
cycle skew is mathematically calculated by taking the
difference between the rising and falling edge propagation
delays. Unequal t_PLH and t_PHL values cause pulse width
distortion which affects the duty cycle. Duty cycle skew is
defined by the following equation and Figures 27 and 28 for
an input and its associated output.
tSKEW(Duty Cycle) + | tPLH−tPHL |
The example shown in Figure 29 defines the within
device skew parameters for a device with two inputs (D1,
D2) and their two associated outputs (Q1, Q2). The within
device skew for this example would be the higher of the
following two equation results:
tSKEW(Within Device) + tPLH2 * tPLH1
tSKEW(Within Device) + tPHL2 * tPHL1
50%
D2
50%
50%
50%
Q2
t_PLH
t_PHL
Figure 27. Single−Ended Duty Cycle Skew
IN2
X_pt
X_pt
IN2
OUT2
X_pt
OUT2
t_PLH
X_pt
t_PHL
Figure 28. Differential Duty Cycle Skew
Skew (Within Device)
Within device skew is the difference between the identical
transition propagation delays of a single multiple output
device with a common input. It is mathematically calculated
by obtaining the rising and falling output propagation delays
for each individual output of the device. The minimum
output propagation delay from the set of delays is then
subtracted from the maximum output propagation delay
from the set of delays as shown in the following equations.
The higher of the two equation results is taken as the within
device skew specification.
tSKEW (Within Device Rising Edge)
+ tPLH(max from set) * tPLH(min from set)
tSKEW (Within Device Falling Edge)
+ tPHL(max from set) * tPHL(min from set)
50%
D1 = D2
50%
50%
Q1
t_PLH1
t_PHL1
50%
50%
50%
Q2
t_PLH2
t_PHL2
Figure 29. Within Device Skew
Skew (Device to Device)
Device to device skew is the difference between the
identical transition propagation delays of two devices with
a common input signal under identical operating conditions
(identical ambient temperature, V_CC, V_EE, etc). It is
mathematically calculated from data sheet propagation
delay values as shown below.
tSKEW (Device to Device) + tPLH(max) * tPLH(min)
+ tPHL(max) * tPHL(min)
Minimum Input Pulse Width
The minimum input pulse width (t_PW) is the shortest pulse
width that will guarantee proper device operation. It is
measured by decreasing the test signal generator pulse width
(i.e., DUT input pulse width) until the DUT outputs no
longer function properly. For single−ended inputs, it is
measured between the 50% points of the rise and fall
transitions as shown in Figure 30.
V_IH
50%
V_IL
t_PW
t_PW
Figure 30. Single−Ended Input Pulse Width
http://onsemi.com
11