ds8908b National Semiconductor Corporation, ds8908b Datasheet

ds8908b

Manufacturer Part Number

ds8908b

Description

Am/fm Digital Phase-locked Loop Frequency Synthesizer

Manufacturer

National Semiconductor Corporation

Datasheet

1.DS8908B.pdf (11 pages)

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C 1995 National Semiconductor Corporation

DS8908B AM FM Digital Phase-Locked

Loop Frequency Synthesizer

General Description

The DS8908B is a PLL synthesizer designed specifically for

use in AM FM radios It contains the reference oscillator a

phase comparator a charge pump an operational amplifier

a 120 MHz ECL I

and a 19-bit shift register latch for serial data entry The

device is designed to operate with a serial data controller

generating the necesary division codes for each frequency

and logic state information for radio function inputs outputs

A 3 96 MHz pierce oscillator and divider chain generate a

1 98 MHz external controller clock a 20 kHz 10 kHz 9 kHz

and a 1 kHz reference signals and a 50 Hz time-of-day

signal The oscillator and divider chain are sourced by the

and time-of-day indication when the balance of the PLL is

powered down

The 21-bit serial data steram is transferred between the fre-

quency synthesizer and the controller via a 3-wire bus sys-

tem comprised of a data line a clock line and an enable

line

The first 2 bits in the serial data stream address the synthe-

sizer thus permitting other devices such as display drivers to

share the same bus The next 14 bits are used for the

PLL(N

select the AM or FM local oscillator input A high level on

this bit enables the FM input and a low level enables the AM

input The 16th and 17th bits are used to select one of the 4

reference frequencies The 18th and 19th bits are connect-

ed via latches to open collector outputs These outputs can

be used to drive radio functions such as gain mute AM

FM or charge pump current source levels

The PLL consists of a 14-bit programmable I

ECL phase comparator an ECL dual modulus (p p

scaler a high speed charge pump and an operational am-

plifier The programmable divider divides by (N

the number loaded into the shift register The programmable

divider is clocked through a

or through a

will work at frequencies up to 15 MHz while the FM input

works up to 120 MHz The VCO can be tuned with a fre-

quency resolution of either 1 kHz 9 kHz 10 kHz or 20 kHz

The buffered AM and FM inputs are self-biased and can be

driven directly by the VCO through a capacitor The ECL

phase comparator produces very accurate resolution of the

phase difference between the input signal and the reference

oscillator The high speed charge pump consists of a

switchable constant current source and sink The charge

pump can be programmed to deliver from 75 mA to 750 mA

of constant current by connection of an external resistor

from pin R

puts Connection of programming resistors to the bit outputs

enables the controller to adjust the loop gain for the particu-

lar reference frequency selected The charge pump will

source current if the VCO frequency is high and sink

TRI-STATE is a registered trademark of National Semiconductor Corp

CCM

pin thus providing a low power controller clock drive

1) divide code The 15th bit is used internally to

PROGRAM

prescaler by the FM input The AM input

L dual modulus programmable divider

to ground or the open collector bit out-

TL F 5111

prescaler by the AM input

L divider an

1) N being

1) pre-

current if the VCO frequency is low The low noise opera-

tional amplifier provided has a high impedance JFET input

and a large output voltage range The op amp’s negative

input is common with the charge pump output and its posi-

tive input is internally biased

Features

Connection Diagram

Uses inexpensive 3 96 MHz reference crystal

thesis at FM frequencies

FM resolution of either 10 kHz or 20 kHz allows usage

of 10 7 MHz ceramic filter distribution

Serial data entry for simplified control

50 Hz output for time-of-day reference driven from sep-

arate low power V

2 open collector buffered outputs for controlling various

radio functions or loop gain

Separate AM and FM inputs AM input has 15 mV (typi-

cal) hysteresis

Programmable charge pump current sources enable ad-

justment of system loop gain

Operational amplifier provides high impedance load to

charge pump output and a wide voltage range for the

VCO input

capability greater than 120 MHz allows direct syn-

See NS Package Number N20A

Order Number DS8908BN

Dual-In-Line Package

CCM

Top View

RRD-B30M105 Printed in U S A

June 1990

TL F 5111 – 1

Related parts for ds8908b

ds8908b Summary of contents

Page 1

... DS8908B AM FM Digital Phase-Locked Loop Frequency Synthesizer General Description The DS8908B is a PLL synthesizer designed specifically for use radios It contains the reference oscillator a phase comparator a charge pump an operational amplifier 2 a 120 MHz ECL I L dual modulus programmable divider and a 19-bit shift register latch for serial data entry The ...

Page 2

Absolute Maximum Ratings If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications Supply Voltage ( CC1 CCM (V ) CC2 Input Voltage Output Voltage DC Electrical Characteristics ...

Page 3

... Note 2 Unless otherwise specified min max limits apply across the Note 3 All currents into device pins shown as positive out of device pins as negative all voltage referenced to ground unless otherwise noted All values shown as max or min on absolute value basis Schematic Diagrams (DS8908B AM FM PLL Typical Input Output Schematics 5111 – ...

Page 4

Schematic Diagrams (Continued 5111 – 5111 – 5111 – 5111 – 8 ...

Page 5

Schematic Diagrams (Continued) Timing Diagrams TL F 5111 – 9 ENABLE vs CLOCK CLOCK vs DATA 5111 – 5111 – 11 ...

Page 6

... Timing diagrams are not drawn to scale Scale within any one drawing may not be consistent and intervals are defined positive as drawn SERIAL DATA ENTRY INTO THE DS8908B Serial information entry into the DS8908B is enabled by a low level on the ENABLE input One binary bit is then ac- ...

Page 7

Typical Application Additional application notes are located at the back of section 11 Electronically Tuned Radio Controller System Direct Drive LED 5111 – 13 ...

Page 8

Logic Diagram 8 ...

Page 9

9 ...

Page 10

... National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications Molded Dual-In-Line Package (N) Order Number DS8908BN NS Package Number N20A 2 A critical component is any component of a life ...

Page 11

... This datasheet has been download from: www.datasheetcatalog.com Datasheets for electronics components. ...

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