Datasheet

10
LT1671
APPLICATIONS INFORMATION
WUU
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Crystal Oscillators
Figure 7 shows a crystal oscillator circuit. In the circuit, the
resistors at the LT1671’s positive input set a DC bias point.
The 2k-0.068µF path sets up phase shifted feedback and
the circuit looks like a wideband unity-gain follower at DC.
The crystal’s path provides resonant positive feedback
and stable oscillation occurs.
Figure 7. 1MHz to 10MHz Crystal Oscillator
Figure 8. Switchable Output Crystal Oscillator. Biasing A or B
High Places Associated Crystal in Feedback Path. Additional
Crystal Branches Are Permissible
–
+
LT1671
2k
5V
2k
1MHz TO 10MHz
CRYSTAL (AT-CUT)
0.068µF
OUTPUT
1671 F07
2k
1671 F08
–
+
LT1671
1k
5V
1k
1k
75pF
D1
OUTPUT
B
A
LOGIC INPUTS
AS MANY STAGES
AS DESIRED
XTAL A
1k
R
X
XTAL B
XTAL X
D2
D
X
2k
= 1N4148
GROUND XTAL CASES
Switchable Output Crystal Oscillator
Figure 8 permits crystals to be electronically switched by
logic commands. This circuit is similar to the previous
examples, except that oscillation is only possible when
one of the logic inputs is biased high.