LA1781M_09 Datasheet, PDF (23/48 Pages) Sanyo Semicon Device – For Car Radios Single-Chip Tuner IC

3D AGC Sensitivity Characteristics
LA1781M
AGC sensitivity
Wide AGC sensitivity
ΔF
1
Second-channel
attenuation improvement
Desired station AGC sensitivity
2
Narrow AGC sensitivity
3
4
V23 (Desired station field strength)
Fig. 6
Figure 6 3D AGC Sensitivity - Δf, V23 characteristics
• The wide AGC sensitivity is determined by the antenna and RF circuit selectivity, regardless of V23.
• The narrow AGC sensitivity is determined by the following.
The total selectivity of the antenna, RF circuit, and mixer when V23 ≥ 0.5V
The above selectivity and V23 when V23 < 0.5V
• The improvement in the second-channel attenuation corresponds to the area occupied by the narrow AGC in the total
AGC sensitivity area.
Figure 8 on the next page shows the actual operation of the circuit.
Δf -- AGC on Level (ANT input)
When Δf = 0, 98.1MHz
110
100
90
80
70
60
50
--5 --4 --3 --2 --1 0 1 2 3 4 5
Δf -- MHz
fD = 98.1MHz Second-dhannel pad
fu = 98.1MHz + Δf
Fig. 7
ANT IN
VIN
No.6038-23/48