Onkyo TX-7430 - PLL Tuned Circuit; Auto Search Tuning Circuit

TX·7430
4. PLL tuned circuit
26 I r- sc
A block diagram of the tuned of the PLL is shown in
the above diagram.
Operation during AM reception
The reception frequency is applied to the pro gr arn ma ble
divider wnere it is divi ded to lI N and outpur as fv . This
is applied to the phase c ornpar aror where it is cornparated
with frequenc y reference fr (9k H z fo r G /W model s a nd
10kHz for D rnodel l . If fr and fv di ffer . Eo equal to the
difference in Ireq uency is output.Since err or outpur Eo
is a
pulse waveforrn . it is passed t hr ough the low pass
filter t o change it into oe volt age Vd , which is applied
to the variable capacitor diode in the front en d to change
the reception frequenc y . Thi s continues unt il fv and fr are
the sarne and Eo·O .
Operation du rin g FM reception
The pulse s wallo w metho d is used in the pr e scaler of thi s
unit . In th is t ype of pre scaler . a supplernent ary number
5. Auto search tuning circuit
TONED
INDICATOR
Q103
8
+B
FM IF&AM
cc
w
SY STEM
-.J
07 03
-.J
12
2 2N 0
TO
P
OCC
STEREO
r-- f--
DE CODER
06
u
Q113
D10 7
N OI SE
1""1
DETECTOR
(chan ged acc ordirng to the program code input) and the
divided reception frequency from the presca ler are
combined in the c ontro! c ounter an d the presca ler' s
divi si
on Iac ror is s wit ch ed 1/16 or 1/!7 acco rding
to
ex tern al co ntro l (I/!6 whe n th e PSC t ermin al is "H "
and 1 /17 when it is " L " ).
The st at ion osc illat or frequenc y is app lied to the program -
m able div ider . but the pr ograrnm abl e d ivider has an upper
frequenc y limit of only 30MHz. so the pulse swallow-type
pr escaler i which can be used up to ISOMHz.is insert ed for
divi sion to 1/Np;
The sign a l is applied to the pr ogr ammab le divider and
divided t o l /N . T he result is c om pared with a 25kHz
frequ ency re fere nce in the phase derector and e rro r
is outpur a s Eo until a rnatch is obta ined as in AM
oper at ion .
During FM recept ion . this is operated by the IF leve l dere c-
ti on a nd zer o cr oss detecti on ci rc uits in cl ud ed in the FM
IF & AM systern IC of Q I03 and by th e no isc co m po nent d ete ct ion
circuit of Q113 .
When a sta tion is tu ned , the o u tp ur o f a ll
ou t puts go t o th e l ow level so Q 703 goes from o n to off,
ca us ing p in
22 of the con tro ller IC t o go to the high leve l
(0 co mp lete 3U to sea rch t unin g.
During AM recepti on. this is operared by the IF level derec-
tion included in th e FM IF & AM system JC of Q I03. When a
station is tumed . Q 703 go es to off, causin g pin 22 of th e co ntr oll er
JC
to go to th e high level to co mplete a ut o search tu ning.
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