LA1787M Datasheet, PDF (23/54 Pages) Sanyo Semicon Device – Single-Chip Tuner IC for Car Radios

LA1787M
2. Modified circuits
The following characteristics have been improved over those of the The LA1784M.
• The AM adjacent channel interference characteristics (∆40 kHz) have been improved.
• The AM S-meter curve slope has been increased.
• The FM separation temperature characteristics have been improved.
• The stereo indicator sensitivity has been improved.
• The FM oscillator circuit has been omitted.
(1) AM interference characteristics improvement
The second signal interference and suppression have been improved for adjacent channels (±40 kHz) by increasing
the AM second mixer input dynamic range.
(2) The AM S-meter curve slope has been increased.
The slope of the AM S-Meter curve has been increased from that of the LA1781M and LA1784M.
AM S-Meter Voltage
7
6
5
4
LA1787M ^LA1780M
3
2
LA1781M
1
–020
0
20
40
60
80 100 120 140
Antenna input — dBµ
(3) FM separation temperature characteristics improvement
The temperature characteristics have been improved, the amount of change in the separation due to drift when at
power on has been stabilized. This makes it easier to adjust the separation.
Change in Separation (LA1781M): First IF Input
60
Change in Separation (LA1787M): First IF Input
60
55
55
50
50
45
45
40
40
35
35
0
1
2
3
0
1
2
3
Time after power on — minutes
Time after power on — minutes
No. 6655-23/54