No. 6276-8/13

LA75675M-S

Continued from preceding page.

Pin No.

Pin

Function

Equivalent circuit

Equalizer circuit

This circuit corrects the frequency characteristics of

the video signal.

Pin 8 is the input to the EQ amplifier. The EQ amplifier

takes a 1.5 Vp-p video signal as its input and amplifies

that to a 2.0 Vp-p level.

• Notes on the equalizer amplifier design

The equalizer amplifier is designed as a voltage

follower amplifier with a gain of about 2.3 dB. If

frequency characteristics correction is required,

insert the capacitor, inductor, and resistor between

pin 7 and ground in series.

• Using the equalizer amplifier

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

R1

—— +1

(Vi + Vin) = Vo

× G

Z

G: Gain of the voltage follower amplifier

Vin: Imaginary voltage

G: About 2.3 dB

Assuming Vin

≈ 0, then AV will be:

VoG

R1

AV = —— = —— + 1

Vi

Z

R1 is an IC internal 1 k

Ω resistor. Simply select a

value of Z according to the desired characteristics.

However, note that the equalizer amplifier gain will be

a maximum at the Z resonance, so care is required to

prevent distortion from occurring.

6

7

8

EQ amp

6

7

8

2.2 k

Ω

40 k

Ω

200

Ω

EQ INPUT

EQ OUTPUT

AGC

C

R

L =Z

1 k

Ω

A12623

A12624

PLL detector APC filter connection

The APC time constant is switched internally by the IC.

When locked, the VCO is controlled by the route A,

and the gain is reduced. When unlocked or during

weak field reception, the VCO is controlled by the

route B, and the gain is increased.

We recommend the following values for this APC filter:

R = 150 to 390

Ω

C = 0.47 µF.

9

APC filter

9

1 k

Ω 1 kΩ 1 kΩ

A

B

FROM

APC DET

A12625

C

+

R

Continued on next page.