LA1245

No.737-5/11

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 1.5k

Ω.

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

when Rg=520

Ω (470Ω + 50Ω)

75dBµ

Pin 9 input

when Rg=50

Ω

53dBµ

Pin 6 input

when Rg=50

Ω

48dBµ

Pin 3 input

when Rg=50

Ω

22dBµ

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)