EL5281C Datasheet, PDF (10/11 Pages) Elantec Semiconductor – Dual 8ns High-Speed Comparator

EL5281C
Dual 8ns High-Speed Comparator
Threshold Detector
The inverting input is connected to a reference voltage
and the non-inverting input is connected to the input. As
the input passes the V_REF threshold, the comparator's
output changes state. The non-inverting and inverting
inputs may be reversed.
VIN
+
VREF
-
VOUT
Crystal Oscillator
A simple crystal oscillator using one comparator of an
EL5281C is shown below. The resistors R₁ and R₂ set
the bias point at the comparator's non-inverting input.
Resistors R₃, R₄, and C₁ set the inverting input node at
an appropriate DC average voltage based on the output.
The crystal's path provides resonant positive feedback
and stable oscillation occurs. Although the EL5281C
will give the correct logic output when an input is out-
side the common mode range, additional delays may
occur when it is so operated. Therefore, the DC bias
voltages at the inputs are set about 500mV below the
center of the common mode range and the 200Ω resistor
attenuates the feedback to the non-inverting input. The
circuit will operate with most AT-cut crystal from 1MHz
to 8MHz over a 2V to 7V supply range. The output duty
cycle for this circuit is roughly 50% at 5V V_CC, but it is
affected by the tolerances of the resistors. The duty cycle
can be adjusted by changing V_CC value.
5V
R1 5kΩ
200Ω
1MHz to
8MHz
+
R2 1.5kΩ -
VOUT
R3
C1
0.01µF
R4
2kΩ
2kΩ
10