LA1245
8. When a cable or something similar is connected to a local oscillation buffer (pin 20), which is equivalent to
connecting a capacitor of about 20pF, the output from the buffer will be of sawtooth waves, causing the level low at
the short wave band. To prevent this, connect a resistor between pin 20 and GND, which will increase the operating
current of the buffer amplifier. Since the maximum current obtained from pin 20 is 2mA, the suitable resistance
between pin 20 and GND is 1.5kΩ.
9. Use a semi-fixed resistor for R to allow the fluctuation of V
.
211
SM
10. When changing an IFT or using an RF tuner, select a filter and related circuits according to the following conditions.
The input levels of each terminal where 30% modulated detection output of –25dBm is obtained are as follows :
Pin 11 input
Pin 9 input
Pin 6 input
Pin 3 input
when Rg=520Ω (470Ω + 50Ω)
when Rg=50Ω
75dBµ
53dBµ
48dBµ
22dBµ
when Rg=50Ω
when Rg=50Ω
Slight change in IFT, however, will be covered by changing the constant of resistors R and R
.
204
202
11. When the coupling coefficient of the local oscillation coil is small and an anti-resonance point of about 100MHz is
present or the stray capacitance between pin 19 and pin 20 is large, the buffer output (pin 20) may be subject to
parasitic oscillation of about 100MHz. In this case, connect a capacitor of about 30pF between pin 20 and GND. To
observe parasitic oscillation, connect a capacitor of 5pF in series with the probe. If the probe is connected direct to
pin 20, the input capacitance of the probe causes parasitic oscillation to stop, which makes it impossible to observe.
Sample Application Circuit 1
Unit (resistance : Ω, capacitance : F)
No.737-5/11
SANYO [ SANYO SEMICON DEVICE ]
