LA1787M Datasheet, PDF (27/54 Pages) Sanyo Semicon Device – Single-Chip Tuner IC for Car Radios

3D AGC Sensitivity Characteristics
LA1787M
AGC sensitivity
Wide AGC sensitivity
∆F
1
Second-channel
attenuation improvement
Desired station AGC sensitivity
2
Narrow AGC sensitivity
3
4
V23 (Desired station field strength)
Fig. 6
A12075
3D AGC Sensitivity — ∆f, 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 ≥ 0.5 V
The above selectivity and V₂₃ when V₂₃ < 0.5 V
• 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.
∆f — AGC on Level (ANT input)
110
100
90
80
70
60
50
–5 –4 –3 –2 –1 0 1 2 3 4 5
∆f — MHz
fD = 98.1 MHz Second-channel pad
ANT IN
VIN
fu = 98.1 MHz + ∆f
A12076
Fig. 7
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