EL5185C - Preliminary
4ns High-Speed Comparator
output changes state. The non-inverting and inverting
inputs may be reversed.
V
+
-
IN
V
OUT
V
REF
Crystal Oscillator
A simple crystal oscillator using one comparator of an
EL5185C 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 EL5185C
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 200W 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 VCC, but it is
affected by the tolerances of the resistors. The duty cycle
can be adjusted by changing VCC value.
1MHz to
5V
8MHz
200W
R
R
5kW
1
2
+
-
V
OUT
1.5kW
R
3
C
1
R
4
2kW
0.01µF
2kW
10
ELANTEC [ ELANTEC SEMICONDUCTOR ]
