LV25700PM Datasheet, PDF (30/68 Pages) Sanyo Semicon Device – For Car Radio Single chip Tuner IC

LV25700PM
AM NC block
This block detects noise from the 10.7 MHz CF out, turns OFF the AM demodulated signal waveform only during the
period affected by noise, and holds the DC. The detection path is the one system of Pin 40 (S-meter AC). AM NC
operation can be monitored by the Pin 24 trigger out. The Pin 47 external constant is determined by the FM NC with
priority.
SA:D
Recommended Setting
Description of Functions
SA24
Nose-AGC Th.
[1]Force
0: Fixes the noise detection sensitivity.
D2
Forced noise AGC
Noise AGC
1: Uses noise AGC in the forcibly applied state.
The noise detection sensitivity can be adjusted by DAC (SA09, D0 to D4) control.
SA22
FIFGAIN
[9]
Sets the IF limiter amplifier gain.
D4-D7
Increasing the DAC setting increases the gain.
Reducing the DAC setting reduces the gain.
SA11
S-meter Shift
[29]
Hides the noise detected by VsmAC.
D0-D4
Increasing the DAC setting increases the shift amount.
Reducing the DAC setting reduces the shift amount.
Reducing the shift amount enhances the effects during weak input, but also
increases the chances of operation errors due to weak input noise.
SA10
D1
AC S-Meter
NC sensitivity switching
[1]
27kΩ
Reduces the AC-S-meter internal load resistance value by approximately half.
(54kΩ//60kΩ → 27kΩ//60kΩ)
0: Normal (Internal load = 54kΩ//60kΩ)
1: ON (Internal load = 27kΩ//60kΩ)
However, note that in FM mode the MRC and IF filter also operate by detecting the
AC component of the same pin (AC_Vsm), so these functions are affected by this
bit.
SA18
Noise-Sens.
[2]
D6-D7 NC load switching
6kΩ
The noise detection sensitivity is adjusted by switching the noise amplifier output
load.
SA09
NC SENS MAIN
[15]
This is valid only in reception mode.
D0-D4 Adjusts the NC noise
However, it is invalid when SA24 D2 is set to OFF (normal).
detection sensitivity
When SA24 D2 is ON
Increasing the DAC setting increases the comparator threshold voltage, and
worsens the noise detection sensitivity.
Conversely, reducing the DAC setting enhances the detection sensitivity.
(However, reducing the DAC setting by too much increases the chances of
operation errors.)
SA19
AM NC STOP
[31]
Can be set to operate only at weak input (forced OFF at strong input).
D0-D4
Increasing the DAC setting → Operates up to strong input.
Reducing the DAC setting → Operates only at weak input.
SA20
D2-D7
AM NC gate
[12]
430μsec
Can set the gate time.
Increasing the DAC setting shortens the gate time.
(Reference value)
Reducing the DAC setting lengthens the gate time.
SA24
AM NC OFF
[0]
Can forcibly set AM NC to OFF.
D6
0 = ON → Normal operation
1 = OFF → Forcibly OFF
* AM NC ON/OFF can be set by the DAC [AM NC OFF].
* The NC sensitivity coarse adjustment can be set by the DAC [AC_Smeter Sw] and the DAC [Noise-Sens].
* The NC sensitivity fine adjustment can be set by the DAC [NC SENS MAIN], the DAC [S-Meter Shift] and the DAC
[FM IF GAIN].
* The gate time can be set by the DAC [AM NC gate].
The ANT-IB-LEVEL range at which AM NC turns ON can be set by the DAC [AM NC stop].
(AM NC can be turned OFF at medium and strong input.)
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