DS8911V ,Sound Up-Conversion Frequency SynthesizerDS8911/DS8913AM/FM/TVSoundUp-ConversionFrequencySynthesizerApril1990DS8911/DS8913AM/FM/TVSoundUp-Co ..
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DS8921AM ,Differential Line Drivers and Receiver PairGeneral DescriptionTTL and CMOS.The DS8921, DS8921A are Differential Line Driver and Re-ceiver pair ..
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DS8911V-DS8913V
Sound Up-Conversion Frequency Synthesizer
TL/F/7398
DS8911/DS8913
AM/FM/TV
Sound
Up-Conversion
Frequency
Synthesizer
April 1990
DS8911/DS8913 AM/FM/TV Sound
Up-Conversion Frequency Synthesizer
General Description
The DS8911isa digital Phase-Locked Loop (PLL) frequen- synthesizer intendedforuseasa Local Oscillator (LO)in
electronically tuned radios. The deviceis usedin conjunc-
tionwitha serial data controller,a loop filter, some varactor
diodes and several passive elementsto providethe local
oscillator functionfor bothAMandFM tuning.
The conventional superheterodyneAM receiver utilizesa
lowIFor down conversion tuning approach wherebytheIF chosentobe belowthe frequenciestobe received.The
DS8911 PLLonthe other hand, utilizesan up-conversion
techniqueintheAM mode wherebythefirstIF frequencyis
chosentobe well abovetheRF frequency rangetobe
tuned. This approach eliminatesthe needfor tuned circuitstheAM frontend sincethe image,halfIF,and other spuri-
ous responses occurfar beyond therangeof frequenciesto tuned. Sufficient selectivityand secondIF image protec-
tionis providedbya crystal filteratthe outputofthefirst
mixer. significant cost savingscanbe realized utilizingthisup-
conversion approachto tuning. RemovaloftheAM tuned
circuits eliminatesthe costof expensive matched varactor
diodesand reducesthe amountof labor requiredfor align-
ment down from6 adjustmentsto2. Additional cost savings
are realized because up-conversion enables boththeAM
andFM bandstobe tuned usinga single Voltage Controlled
Oscillator (VCO) operating between98and120 MHz. (Theto1LO tuning range foundin conventionalAM down con-
version radiosis reducedtoa 10% tuning range; 9.94 MHz 11.02 MHz).
Up-conversionAM tuningis accomplishedbyfirst dividing
the VCO signal downbya modulus10to obtaintheLO
signal. ThisLOinturnis mixedon chipwiththeRF signalto
obtainafirstIFatthe MIXER output pins. ThisfirstIF after
crystal filteringis mixed (externally) witha referencefre-
quency providedbythe PLLto obtaina450kHz secondIF
frequency. The DS8911 derivesthe450 kHz secondIFby
mixingan 11.55 MHzfirstIF witha 12.00 MHz reference
frequency.andWB (weather band) tuningis done usingthe con-
ventional down conversion approach. Herethe VCO signal bufferedto producetheLO signaland then mixedon chip
withtheRF signalto obtainanIF frequencyatthe MIXER
output pins. ThisIF frequencyis typically chosentobe 10.7
MHz although placementat 11.50 MHz canfurther enhance mode performanceand minimizeIF circuitry.
The PLL provides phase comparator reference frequencies10, 12.5,25,and100 kHz.The tuning resolutions result-
ing from these reference frequenciesare determinedbydi-
vidingthe referencebythe premix modulus. TableII shows
the tuning resolutions possible.
The DS8911 containsthe following logic elements:a volt-
age controlled oscillator,a reference oscillator,a 14-bit pro-
grammable dual-modulus counter,a reference frequencydi-
vider chain,a premix divider,a mixer,a phase comparator,a
charge pump,an operational amplifier,and control circuitry
for latched serial data entry.
The DS8913 includesallthe above logic elements except
thatit requiresa10 MHz reference frequency insteadof MHz.
Features Direct synthesisof LW, MW, SW,FM,andWB
frequencies Serial data entryfor simplified processor control10, 12.5,25,and100 kHz reference frequencies8 possible tuning resolutions (see TableII)Anop amp with high impedance inputsfor loop filtering Programmable mixer with high dynamic range
TRI-STATEÉ isaregistered trademarkof National SemiconductorCorporation.
MICROWIRETMis atrademarkof National SemiconductorCorporation.
C1995National SemiconductorCorporation RRD-B30M105/PrintedinU.S.A.
