la1145 Sanyo Semiconductor Corporation, la1145 Datasheet - Page 11

• Manufacturer Part Number: la1145
• Description: Fm If System Quadrature Detector For Car Radio
• Manufacturer: Sanyo Semiconductor Corporation

Soft Mute Characteristics
1.
2.
3.
Control
The S/N setting (C/N) for weak inputs and the –3 dB limiting sensitivity can be controlled by obtaining the proper value for
the un-soft muted input/output signal characteristic. However, usable sensitivity cannot be controlled as this is determined by
the front end and IF design which are unrelated to soft muting.
Soft mute setting
Soft mute operation depends on the S-meter circuit voltage and the hole
detection circuit voltage. As shown in the graph on the right, the degree
of soft muting correlates with the mute drive voltage, V15. The control
signal line of the mute drive voltage switches before and after the
10 dBµ ANT divergence point.
When adjusting the soft mute with a weak signal which does not affect
the S-meter, first adjust it using the hole detection input signal. However,
as the S-meter output will readjust the soft mute level, also adjust the
soft mute using the S-meter output. At this point, the hole detection
output adjusts the gain up to the IF input, causing a variance. Also, the
S-meter output is varied by the value of R
The LA1145 differs from the LA1140 in that it works with the internal
soft mute circuit continuously engaged.
Soft mute transition response characteristic
The degree of soft muting automatically varies according to the change in input field strength. Omitting the influence of the
front end wideband AGC circuit, the LA1145’s response speed is dependent on the time constant at pins 15 and 16.
I/O Characteristics (Mute Start Point)
I/O Characteristics (R
ANT input level – dBµ
IF input level, – dBµ
CT
= 0
16
.
)
LA1145, 1145M
I/O Characteristics (Mute Gradient)
Mute Driver Voltage Characteristics
ANT input level – dBµ
IF input level – dBµ
ANT input level (dBµ)
Hole detector
S-meter
(Adjust R4, R5)
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