LA1135M 데이터 시트보기 (PDF) - SANYO -> Panasonic

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LA1135M

AM Tuner System for Car Radios and Home Stereos

SANYO -> Panasonic 

LA1135, 1135M

16. Measure against suppression of sensitivity in the presence of an undesired signal of high strength

(Sample application where two PIN diodes are used in the antenna damping circuit)

The LA1135 contains the wide-band AGC circuit (wide-band AGC with pin 2 input) against cross modulation which occurs

because an undesired signal of high strength distorts the FET input. The AGC = ON level depends on the value of external

resistor R3 as shown below.

Test conditions

Double-tuning

ANT input level

at which ANTD is turned ON when

fu = 1.4 MHz is inputed at fr = 1 MHz

Resistor value, R – Ω

When a nonlinear element, such as transistor, is used for antenna damping, cross modulation which occurs when the transistor is

turned ON is as shown below.

Cross modulation characteristic which is caused

by the ANT Tr when the

LA1135 wide-band

AGC-ON level (with

pin 2 input) is varied

Double-

tuning

Cross Modulation Characteristics

Desired:1.0 MHz 400 Hz 30% mod 74 dBµ

Undesired: 1.4 MHz non-mod

Wide-band AGC (pin 2 input)75Ω

Desired: 1.0 MHz 400 Hz

non-mod 74 dBµ

Undesired: 1.4 MHz 1 kHz

80% mod

Unit (resistence: Ω, capacitance: F)

Cross modulation which occurs when the

transistor for ANT damping is turned ON

Undesired input – dBµ

The dynamic range of the FET input covers up to approximately 110 dBµ of antenna input, but the AGC-ON level must be set

lower because of the bad effect shown above.

Therefore, there are some cases where it is difficult to receive a desired signal of low strength in the presence of an an undesired

signal of high strength. To solve this problem, a sample application circuit where two PIN diodes with good linearity are used for

antenna damping and its cross modulation characteristic are shown below.

Sample Application Circuit where two PIN diodes are used for ANT damping

Equivalent capacitance available

(Capacitance is desirable because

of a slight change in ANT damping

in the band)

(Approximately 3000 pF)

Double-

tuning

Unit (resistance: Ω, capacitance: F)

No. 1272-9/18

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