LV25700PM Datasheet, PDF (27/68 Pages) Sanyo Semicon Device – For Car Radio Single chip Tuner IC

LV25700PM
AM IF AGC
The AM IF AGC gain is controlled by the Pin 44 DC voltage.
IF AGC time constant switching circuit
This circuit prevents the system from erroneously stopping (or passing through) caused by S-meter oscillation due
to transient response of IF AGC (2nd order filter) in seek mode.
Reception mode: 2nd order filter consisting of C at Pin 65 and Pin 66.
Seek mode: The internal transistor turns ON and a first order filter is formed by 110Ω and C65.
AM S-meter
The AM S-meter has two systems: AC and DC.
S-meter (AC): Picks up from the 10.7MHz path. The band is determined by the ceramic filter, and the S-meter is
used as AM NC pulse detection. The output is Pin 57, and the AC component is determined by the
external capacity value.
(In FM mode, S-meter operates linked to the FM NC, MRC and neighboring interference (IF filter).
S-meter (DC): Picks up from the 450kHz path. The band is determined by the 450kHz ceramic filter, and the S-
meter is used for AM SD and AM HCC. The output is Pin 44, and the signal is converted to a DC
voltage according to the external capacity value.
(In FM mode, S-meter operates linked to the FM SD, FM SNC, FM HCC and FM mute.)
10.7MHz
W
AGC
70
73
70
68
MIX2
62
IF AGC AMP
AM_LC
66
1st IF
RF
AGC
N
AGC
SA15
AM IF GAIN
DET
60 DET OUT
VCA ^10.25MHz
SA22
FM IF SGAIN
10.7MHz
SA11
S-meter
VSM SHIFT
IF 65 LPF
AGC
8 IF AGC
AM
S-meter
SA21
AM VSM SHIFT
AM ON
56
AM_RFAGC AM_ATT
57 44
S-meter(sub) S-meter
The S-meter (AC) can be adjusted by S-meter Shift. At input levels above 20dBμ the gain is lowered by a limiter
amplifier to prevent AM NC detection errors. The recommended setting is 29.
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