LT1720 Linear Technology, LT1720 Datasheet - Page 15

• Manufacturer Part Number: LT1720
• Description: 4ns/ 150MHz Dual Comparator with Independent Input/Output Supplies
• Manufacturer: Linear Technology

APPLICATIONS
applications. This circuit works well because of the two
matched delays and rail-to-rail style outputs of the LT1720.
The circuit in Figure 9 shows a crystal oscillator circuit that
generates two nonoverlapping clocks by making full use of
the two independent comparators of the LT1720.
C1 oscillates as before, but with a lower reference level,
C2’s output will toggle at different times. The resistors set
the degree of separation between the output’s high pulses.
With the values shown, each output has a 44% high and
Figure 8. Timing Skew of Figure 7’s Circuit
1000
800
600
400
200
0
2.5
2.7V TO 6V
3.0
U
V
CC
620
2k
3.5
SUPPLY VOLTAGE (V)
INFORMATION
U
4.0
220
1.3k
Figure 9. Crystal-Based Nonoverlapping 10MHz Clock Generator
4.5
2.2k
1/2 LT1720
CRYSTAL (AT-CUT)
+
–
W
+
1/2 LT1720
–
5.0
C2
C1
10MHz
0.1 F
GROUND
5.5
1720/21 F08
CASE
2k
6.0
U
OPTIONAL—
SEE TEXT
1k
0.1 F
56% low duty cycle, sufficient to allow 2ns between the
high pulses. Figure 10 shows the two outputs.
The optional A1 feedback network shown can be used to
force identical output duty cycles. The steady state duty
cycles of both outputs will be 44%. Note, though, that the
addition of this network only adjusts the percentage of
time each output is high to be the same, which can be
important in switching circuits requiring identical settling
times. It cannot adjust the relative phases between the two
outputs to be exactly 180 apart, because the signal at the
input node driven by the crystal is not a pure sinusoid.
LT1636
A1
Figure 10. Nonoverlapping Outputs of Figure 9's Circuit
2V/DIV
2V/DIV
+
–
Q0
Q1
100k
100k
0.1 F
OUTPUT 1
OUTPUT 0
20ns/DIV
LT1720/LT1721
1720/21 F09
15