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VFB1 17
RS
ViIF
0.1
µF
0.1 µF
VilF 15
RS
VFB2 16
0.1
µF
VS
25 kΩ
25 kΩ
4-STAGE
LIMITER/
AMPLIFIER
LEVEL
DETECTOR
560
33 pF
pF
33
IF1 pF
3
L(2)
IF2 RES2
76
15 kΩ
750
Ω
15 kΩ
RES1
4
MUTING
250
Ω
QUADRATURE
DEMODULATOR
TDA1576
0.1 µF
5.5
kΩ
+
10 Ω
47 µF
VP
(15 V)
1
CPS
2
8.3 kΩ
AFC
voltage
+
−
3.7 3.7
kΩ kΩ
8
VoAF1
9
VoAF2
(3.3 kΩ)
C8-9(1)
VoAF
INDICATOR
DRIVER
20 kΩ
STANDBY
SWITCH
4V
(6 VBE)
INTERNAL
POWER
SUPPLY
1.7 V
5.3 V
(185 VT)
DETUNE
DETECTOR
G
I11 =
0.5 mA
13
VF
3.6 kΩ
14
VF0
5
FMON
12
Vref
220 kΩ
11
Vo(det)
A 1 mA
1
(25 kΩ)
nF
(AM)
field
strength
indicator
level output
for
field strength
zero adjustment
of field strength
indicator
FM
on
10 kΩ
+
(<23 V)
reference
voltage
0.47 µF
detune
voltage
Z8-10
(240
kΩ)
Z9-10
(180
kΩ)
10 Vi(det)
18
GND
MGE456
(1) For 50 µs de-emphasis: C8−9 = 6.8 nF; for stereo operation C8−9 = 56 pF.
(2) L = 0.38 µH; Qo = 70; QL = 20; adjusted to minimum 2nd harmonic distortion (d2); at Vi = 1 mV; coil: 6 turns CuL (0.25 mm) on coil former KAN (C).
Fig.1 Block diagram and test circuit.