LA3370 데이터 시트보기 (PDF) - SANYO -> Panasonic

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LA3370

PLL FM Multiplex Stereo Demodulator for Car Stereo

SANYO -> Panasonic 

LA3370

(3) HCC (high-cut control)

In region B where S/N deteriorates to 40dB or worse even for monaural, the S/N as sensed by the human ear can be

enhanced by suppressing levels at frequencies above approximately 7kHz. Treble region levels that follow meter

voltages can be smoothly attenuated (high-cut control) by impressing IF stage signal meter output to the HCC pin

(pin7) of the LA3370. Fig.7 shows MPX output frequency characteristics (monaural) provided by voltage impressed

on pin 7. Frequency characteristics for a 100% high cut can be determined by an external capacitor connected to pin

4. An equivalent circuit is shown below where the designation is made by the 5kΩ and the C time constant.

Approximate values provided by C as expressed in attenuation at 10kHz are listed in table below : right.

Fig. 8 shows the relation between voltages impressed on pin 7 and rates (%) of high cut (HCC). When IF meter

output voltage characteristics and region B, S/N characteristics, of Fig. 2 have been obtained, S/N improvement by

HCC can be drawn in a way similar to drawing SNC chracteristics.

Fig.2 shows typical meter outputs of a quadrature detection IF amplifier IC. (Fig. 1 shows data for LA1140) HCC

characteristics have been designated to permit region B improvements when the IC is directly connected to HCC

(pin 7) terminal of the LA3370. The infinitesimal control currents at pin 7, similar to pin 8, do not affect meter

outputs.

(4) SNC and HCC connection circuits when coupled with the IF stage.

Fig. 1 shows sample S/N characteristics via antenna inputs when SNC and HCC are connected with the IF stage by

an external circuit.

(5) S/N improvements in region C of Fig.1

Because S/N ratios deteriorate even further in the region C of Fig. 1, it is better to improve the S/N in this region

with IF mutings. The LA1140 is available to linearly vary the IF muting. Employment of the LA3370 together with

the LA1140 further enhances S/N improvement.

No.619-5/11

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