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| 型號(hào)： | LA1781M |
| 廠商： | Sanyo Electric Co.,Ltd. |
| 英文描述： | Single-Chip Tuner IC for Car Radios |
| 中文描述： | 單芯片調(diào)諧器IC的汽車收音機(jī) |
| 文件頁數(shù)： | 23/50頁 |
| 文件大?。?/td> | 567K |
| 代理商： | LA1781M |
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No. 6038-23/50
LA1781M
Notes on second-channel attenuation suppression
Keyed AGC (3D AGC) is a technique for achieving good characteristics for both intermodulation and second-
channel attenuation at the same time. When the desired signal is faint or nonexistent, the high-band AGC level will
be essentially 0, and as a result automatic tuning may malfunction and blocking oscillation may occur in the
presence of strong interfering stations. Keyed AGC helps resolve these problems.
This 3D AGC technique uses information that has the following three frequency characteristics and is a unique
Sanyo-developed system for determining the high-band AGC level.
RF and ANT circuit information: Mixer input AGC
Mixer circuit information: Mixer output AGC
CF selectivity information: S-meter output
–4
–5
–2
–3
–1
f — MHz
0
50
70
80
90
100
110
60
1
2
3
4
5
Pin 58 capacitor:
10 pF
N
μ
f — AGC on Level (ANT input)
Pin 58 capacitor:
47 pF
39
keyed AGC
Fig.3
140
130
120
110
100
90
80
70
71.0
2
3
5
7 10
Frequency, f — MHz
2
3
5
7100
2
3
5
Wide AGC on level frequency characteristics
Narrow AGC on level frequency characteristics
AGC input level frequency
characteristics such that
V
RF
AGC (pin 2) falls under 2 V.
P
μ
W-AGC, N-AGC — f
Fig.5
–4
–5
–2
–3
–1
f — MHz
0
50
60
70
80
90
100
110
1
2
3
4
5
Pin 55 capacitor: 3 pF
Pin 55 capacitor: 10 pF
W
μ
f — AGC on Level (ANT input)
39
5V
keyed AGC
Fig.4
3D AGC Features
Feature
Merit
Only the narrow AGC sensitivity (operation at
f < 1.5 MHz) is
controlled by the field strength of the desired station.
Effective in resolving second-channel attenuation problems.
The narrow AGC sensitivity is controlled by a voltage (V
23
) that is
under 0.5 V.
Allows effective resolution of second-channel attenuation problems without
degrading three-signal characteristics.
Seek operations may stop incorrectly due to the occurrence of
intermodulation.
It is possible to prevent the occurrence of intermodulation in the RF tuning
circuit and antenna in the presence of strong interfering stations, and
blocking oscillation due to AGC operation can be prevented.
The wide AGC can operate even when V
23
= 0 (when the desired
station is not present).
The narrow and wide AGC sensitivities can be set independently.
(See figure 3 and 4.)
Settings can be optimized for the field conditions.
The system has two AGC systems: narrow and wide AGC.
(See figure 5.)
Since the narrow AGC operates for the desired station and adjacent
stations, the wide AGC sensitivity can be lowered and AGC malfunction
due to local oscillator signal can be prevented.
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| LA1781M_09 | 制造商:SANYO 制造商全稱:Sanyo Semicon Device 功能描述:For Car Radios Single-Chip Tuner IC |
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