LV25700PM Datasheet, PDF (23/68 Pages) Sanyo Semicon Device – For Car Radio Single chip Tuner IC

FM IF Filter (BPF)
LV25700PM
1. Detection
The following types of detection are performed, and when there is a response to any detection, the IF filter bandwidth
is reduced.
When there is no response, the bandwidth remains wide. (-3dB BW: 40 to 180kHz)
(1) Modulation index detection: Detects the modulation index of the FM DET OUT block
(2) Neighboring interference detection: Detects neighboring interference
(3) AFC detection: Detects the AFC voltage of the FM DET block
2. Control
The sensitivity of each of the above detection functions is adjusted by BIT. Control is self-contained within AKAGI.
The control voltage is generated from neighboring interference detection, modulation index detection, and AFC
detection.
Thus, ultimately the IF filter band is adjusted using a single control voltage.
This control voltage varies only the IF filter band.
The control voltage can be fixed from the main microcontroller, so the 40 to 180kHz band can also be adjusted by
main microcontroller control. (Fine adjustment is possible in approximately 50 steps.)
(1) IF filter modulation index detection
Detection output: Detects the audio signal level from NCIN (Pin 59)
LPF fc = 70kHz (1st order). The low pass filter is fixed inside the IC.
IC internal control is performed so that the modulation index detection function operates at a certain electric field
strength or less. (The electric field threshold value can be changed by BIT.)
When modulation index detection operates, the IF filter bandwidth is reduced.
The modulation index detection function does not perform control to widen the IF filter bandwidth.
IF1=10.7MHz
75
73
1st IF
S-
meter
SD
ST
DC
SELCT
IF2=450kHz
70
MIX2
BPF
DET
10.25MHz
Neighboring
interference
detection
Control voltage
Filter
Control
AFC
Modulation
index
detection
fc=100k*3
Noise Cancellar
Multiplex
HPF=100k*4
LPF =100k*1
+
10kΩ
-
150Ω
fc=70k*1
DET OUT
60
59
NC IN
27
24
SD/ST-IND DC MONITOR
18
Signal Quality
28
Q-OUT
71
MOD_DET
1μF
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