16
LT1394
1394f LT/TP 0499 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1998
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
TYPICAL APPLICATION
U
Voltage-Controlled Crystal Oscillator (VCXO)
Figure 20, a variant of the basic crystal oscillator, permits
voltage tuning the output frequency. Such voltage-con-
trolled crystal oscillators (VCXO) are often employed
where slight variation of a stable carrier is required. This
example is specifically intended to provide a 4× NTSC
sub-carrier tunable oscillator suitable for phase locking.
The LT1394 is set up as a crystal oscillator, operating
similarly to Figure 3 (a). The varactor diode is biased from
the tuning input. The tuning network is arranged so a 0V
to 5V drive provides a reasonably symmetric, broad tuning
range around the 14.31818MHz center frequency. The
indicated selected capacitor sets tuning bandwidth. It
should be picked to complement loop response in phase
locking applications. Figure 21 is a plot of tuning input
voltage versus frequency deviation. Tuning deviation from
the 4× NTSC 14.31818MHz center frequency exceeds
±240ppm for a 0V to 5V input.
PART NUMBER DESCRIPTION COMMENTS
LT1016 UltraFast Precision Comparator Industry Standard 10ns Comparator
LT1116 12ns Single Supply Ground-Sensing Comparator Single Supply Version of LT1016
LT1671 Fast Single Supply Comparator 60ns, 450µA Single Supply Comparator
LT1720 UltraFast Dual Single Supply Comparator Dual 4.5ns, 4mA Single Supply Comparator
RELATED PARTS
Figure 21. Control Voltage vs Output Frequency for Figure 15.
Tuning Deviation from Center Frequency Exceeds ±240ppm
INPUT VOLTAGE (V)
0
FREQUENCY DEVIATION (kHz)
2
4
5
9
8
7
6
5
4
3
2
1
0
1394 F21
13
14.314.0MHz
14.31818MHz
14.3217MHz
Figure 20. A 4× NTSC Sub-Carrier Voltage-Tunable Crystal Oscillator. Tuning Range
and Bandwidth Accommodate Variety of Phase Locked Loops
1394 F20
–
+
LT1394
5V
390Ω
200pF
* 1% FILM RESISTOR
** NORTHERN ENGINEERING LABS C-2350N-14.31818MHz
*** C SELECT SETS TUNING BANDWIDTH. SET TO COMPLEMENT
LOOP RESPONSE IN PHASE LOCKING APPLICATIONS
†
VARACTOR DIODE
5V
FREQUENCY
OUTPUT
3.9k*
V
IN
0V TO 5V
1M
MV-209
†
2k
2k
100pF
15pF
Y1**
100pF
C SELECT***
0.047µF
1M
1M
1M*
1N4148
LT1004-2.5
47k*
1k*
