7
LTC1520
APPLICATIONS INFORMATION
WUU
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
Figure 10. Temperature Stable Ring Oscillators
–
+
–
+
1/4 LTC1520
–
+
1/4 LTC1520
9.3MHz
OSCILLATOR
WITH BETTER
THAN 45/55
DUTY CYCLE
TYPICAL STABILITY
±5% OVER TEMPERATURE
1/4 LTC1520
3.3k
5V
0.01µF
3.3k
–
+
–
+
1/4 LTC1520
–
+
1/4 LTC1520
–
+
1/4 LTC1520
6.9MHz
OSCILLATOR
OUTPUT
1/4 LTC1520
0.01µF
1520 F10
Layout Considerations
A ground plane is recommended when using a high
frequency device like the LTC1520. A 0.1µF ceramic by-
pass capacitor less than 1/4 inch away from the V
DD
pin is
also recommended. Good bypassing is especially needed
when all four channels are driven simultaneously by the
same input. Under these conditions, and with a bypass
capacitor more than 1 1/4 inches away from the V
DD
pin,
the parasitic inductances will cause ringing in the V
DD
and
output pins. This in turn can cause false triggering of the
output short-circuit detector (Figure 11). When the by-
pass capacitor is placed close to the V
DD
pin, however, the
LTC1520 operates normally (Figure 12).
Figure 9. Tapped Delay Line with 18ns Steps
–
+
0ns DELAY
INPUT
1/4 LTC1520
–
+
18ns DELAY
1/4 LTC1520
–
+
36ns DELAY
1/4 LTC1520
–
+
54ns DELAY
72ns DELAY
1/4 LTC1520
3.3k
5V
0.01µF
3.3k
1520 F09
100-FT TWISTED PAIR
*MC10116
R
T
120Ω
1520 F08
100Ω
100Ω
100Ω
5V
5V
5V
*
100Ω
–
+
1/4 LTC1520
Figure 8. Differential Transmission Over Long Distances
LTC1520 receiving differential data from a PECL driver. As
in the single-ended configurations, care must be taken to
properly terminate the differential data lines to avoid
unwanted reflections, etc.
Alternate Uses
The tightly controlled propagation delay of the LTC1520
allows the part to serve as a fixed delay element. Figure 9
shows the LTC1520 used as a tapped delay line with 18ns
±3ns steps. Several LTC1520s may be connected in series
to form longer delay lines. Each tap in the delay line is
accurate to within ±17% over temperature.
As shown in Figure 10, the LTC1520 can be used to create
a temperature stable ring oscillator with period incre-
ments of 36ns. Low skew and good channel-to-channel
matching enable this oscillator to achieve better than a 45/
55 duty cycle (the duty cycle approaches 50/50 as more
LTC1520s are used for lower frequencies). Note that the
fixed voltage bias may either be created externally with a
resistor divider or generated internally using a bypass
capacitor and the internal open circuit bias point (approxi-
mately 3.3V). The use of the internal bias point will result
in a 1% to 2% distortion of the duty cycle.
