No. 5734-8/13

LA75691

Continued from preceding page.

Pin No.

Pin

Function

Equivalent circuit

close to the IC as possible.

5

Equalizer circuit. This circuit corrects the frequency

characteristics of the video signal.

Pin 17 is the equalizer amplifier input. A 1.5-V p-p signal is

input to pin 17, and that signal is amplified to be a 2-V p-p

signal by the equalizer amplifier.

Equalizer amplifier design:

The equalizer amplifier is designed as a voltage-follower

amplifier with a gain of about 2.3 dB. Connect an inductor, a

capacitor, and a resistor in series between pin 7 and ground

if the frequency characteristics require correction.

Notes on the equalizer amplifier:

If the input signal is vi and the output signal is vo, then:

R1

—— +1 (vi + vin) = Vo

× G

Z

G: The voltage-follower amplifier gain.

vin: Imaginary short

G: About 2.3 dB

Assuming that vin is 0, then:

VoG

R1

AV = ——— = —— +1

Vi

Z

R1 is the IC internal resistance of 1 k

Ω. Simply select Z to

match the desired characteristics. However, note that Z must

be chosen carefully in order not to cause distortion, since the

equalizer amplifier gain will be maximum at the resonance

determined by Z.

6

7

8

EQ amp

PLL detector APC filter

The APC time constant is switched internally in the IC. When

locked, the VCO is controlled by loop A, and the gain is

reduced. When unlocked and in weak field reception, the

VCO is controlled by loop B, and the gain is increased.

For this APC filter the recommended values are:

R should be between 150 and 390

Ω.

C should be 0.47 µF.

9

APC FILTER

Continued on next page.