AND8090 Datasheet, PDF (7/20 Pages) ON Semiconductor – AC Characteristics of ECL Devices

AND8090/D
DIFFERENTIAL CHARACTERISTICS
Section Note − This section explains concepts that only
apply for differential inputs and/or outputs. Differential
inputs and outputs have true and inverted pins, and are often
referred to as “complimentary” inputs and outputs. An
example of a differential input is a true data input (D), and
an inverted data input (D).
Differential Input Application – True and inverted input
signals must be applied in order to obtain accurate
differential test measurements for differential input devices.
The true output of the pulse generator is connected to the true
input of the DUT, and the inverted output of the pulse
generator is connected to the inverted input of the DUT.
Unused Output Termination – An unused output of a
differential pair must be terminated in the same manner as
the used output in order to obtain accurate measurements.
Differential Crosspoint – Differential crosspoints are
used as a measurement point for differential input and
differential output signals. A differential crosspoint (X_pt) is
located where the true and inverted inputs or outputs
intersect as shown in Figure 11.
D or Q
Test Input Swing – The typical AC test input swing for
differential inputs is shown below:
VPP _{(AC Test)} + | VIN _(true) * VIN _(inverted) | + 750 mV
Common Mode Range – The most positive of the true
and inverted input voltages (i.e., the HIGH level) must be
within the differential HIGH input common mode range
(V_IHCMR) for proper operation. To restate, the common
mode range places an upper and lower boundary on the
differential HIGH input level. The HIGH input common
mode range is specified in relation to the input voltage swing
(V_PP). The relationship is determined by the device type, so
refer to the device data sheet for specific information. The
differential HIGH input common mode range is defined by
the following equations.
VIHCMR(min) v VIH v VIHCMR(max)
VIHCMR(max) varies 1 : 1 with VCC
VIHCMR(min) varies 1 : 1 with VEE
The example shown in Figure 13 is typical, and specifies
the common mode range with respect to the entire V_PP
range.
V_IHCMR(max)
X_pt
V_IH for all V_PP
D or Q
Figure 11. Differential Input/Output Crosspoint
Input Voltage Swing – The minimum input voltage
swing (V_PPmin) is found by decreasing the swing between
the true and inverted inputs until the device no longer
performs its specified function. The maximum input voltage
swing (V_PPmax) is determined by the internal circuitry of a
specific device. The differential input voltage swing is
defined by the following equations and Figure 12.
V_PP = | V_IN(true) − V_IN(inverted) |
V_PP(min) v V_PP v V_PP(max)
V_IHCMR(min)
Figure 13. Common Mode Range
The MC100LVEL14 example shown in Figure 14
specifies the common mode range with respect to two V_PP
ranges.
V_IHCMR(max)
2.9 V
V_IH for V_PP < 0.5 V
V_IHCMR(min)
1.2 V
D
V_PP(min)
X_pt
V_PP(max)
D
Figure 12. Differential Input Voltage Swing
V_IHCMR(max)
2.9 V
V_IH for V_PP w 0.5 V
V_IHCMR(min)
1.4 V
Figure 14. MC100LVEL14 Common Mode Range
http://onsemi.com
7