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SP8855E Datasheet(PDF) 6 Page - Zarlink Semiconductor Inc |
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SP8855E Datasheet(HTML) 6 Page - Zarlink Semiconductor Inc |
6 / 14 page 6 SP8855E Advance Information Description Prescaler and AM counter The programmable divider chain is of AM counter construction and therefore contains a dual modulus front end prescaler, an A counter which controls the dual modulus ratio and an M counter which performs the bulk multi-modulus division. A programmable divider of this construction has a division ratio of MN+A and a minimum integer steppable division ratio of N(N-1), where N is the prescaler ratio. Programming The device is programmed by connecting the programming pins to either V CC or ground. The programming inputs will go high if left open circuit but for best noise immunity a wired connection to V CC is preferable. The programming inputs can be driven from TTL or CMOS logic levels if required. Reference input The reference source can be either driven from an external sine or square wave source of up to 100MHz or a crystal can be connected as shown in Fig. 5. Phase Comparator and Charge pump The SP8855E has a digital phase/frequency comparator driving a charge pump with programmable current output. The charge pump current level at the minimum gain setting is approximately equal to the current fed into the R set input pin 19 and can be increased by programming pins 40 and 41 according to Table 1 by up to 4 times. Figure 5 - Typical application diagram APPLICATION USING CRYSTAL REFERENCE 29 SP8855 27 28 33p 100p 10MHz CRYSTAL VCC RF COUNTER PROGRAMMING 1k VCO 1n 7 8 9 10 11 12 13 14 15 16 17 39 38 37 36 35 34 33 32 31 30 * VALUES DEPEND ON APPLICATION 2k2 1n 10n *100n 1 µ 10n 1n Ref in Fpd Fref * - + OP27 ETC 100n +30V * * VCC LOOP FILTER REFERENCE COUNTER PROGRAMMING +5V Pin 40 Pin 41 Current Multiplication Factor 0 0 1.0 0 1 1.5 1 0 2.5 1 1 4.0 Table 1 |
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