LT1394 UTYPICAL APPLICATIONVoltage-Controlled Crystal Oscillator (VCXO) 9 14.3217MHz 8 Figure 20, a variant of the basic crystal oscillator, permits 7 voltage tuning the output frequency. Such voltage-con- 6 trolled crystal oscillators (VCXO) are often employed 5 where slight variation of a stable carrier is required. This 14.31818MHz example is specifically intended to provide a 4 × NTSC 4 sub-carrier tunable oscillator suitable for phase locking. 3 2 FREQUENCY DEVIATION (kHz) The LT1394 is set up as a crystal oscillator, operating 1 similarly to Figure 3 (a). The varactor diode is biased from 14.314.0MHz 0 the tuning input. The tuning network is arranged so a 0V 0 1 2 3 4 5 INPUT VOLTAGE (V) to 5V drive provides a reasonably symmetric, broad tuning 1394 F21 range around the 14.31818MHz center frequency. The indicated selected capacitor sets tuning bandwidth. It Figure 21. Control Voltage vs Output Frequency for Figure 15. Tuning Deviation from Center Frequency Exceeds ± 240ppm 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. 5V 1N4148 47k* 3.9k* VIN 0V TO 5V 1M C SELECT*** 1M* LT1004-2.5 1k* 0.047µF 1M 5V MV-209† 1M 2k 100pF 390Ω Y1** 15pF 100pF + LT1394 – FREQUENCY OUTPUT * 1% FILM RESISTOR 2k ** NORTHERN ENGINEERING LABS C-2350N-14.31818MHz *** C SELECT SETS TUNING BANDWIDTH. SET TO COMPLEMENT 200pF LOOP RESPONSE IN PHASE LOCKING APPLICATIONS † VARACTOR DIODE 1394 F20 Figure 20. A 4 × NTSC Sub-Carrier Voltage-Tunable Crystal Oscillator. Tuning Range and Bandwidth Accommodate Variety of Phase Locked LoopsRELATED PARTSPART NUMBERDESCRIPTIONCOMMENTS 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 1394f LT/TP 0499 4K • PRINTED IN USA 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1998
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