LA7567GM Datasheet, PDF (9/14 Pages) Sanyo Semicon Device – TV and VCR VIF/SIF IF Signal-Processing Circuit with NTSC SPLIT Support

Continued from preceding page.
Pin No.
Pin
LA7567GM
Description
Equivalent circuit
• Equalizer circuit. This circuit is used to correct the video
signal frequency characteristics.
Pin 8 is the EQ amplifier input. This amplifier amplifies a
1.5-V p-p video signal to 2-V p-p.
2kΩ
1kΩ
6
EQ OUTPUT
• Notes on equalizer amplifier design
The equalizer amplifier is designed as a voltage follower
amplifier with a gain of about 0 dB. When used for
frequency characteristics correction, a capacitor, inductor,
and resistor must be connected in series between pin 7
and ground.
7
• Approach used in the equalizer amplifier
If vi is the input signal and vo is the output signal, then:
6
7
EQ amp
R1
——
2
+1
(vi
+
vin)
=
Vo
×
G
8
Where G is the voltage-follower amplifier gain.
Assume:
vin: Imaginary short
G: About 0 dB
vin ≈ 0.
Then:
voG R1
AV = —— = —— +1
vi Z
C
L =Z
R
A13683
• R1 is the IC internal resistance, and is 1 kΩ. In the
application design, simply select Z to correspond to the
desired characteristics. However, since the EQ amplifier
gain will be maximum at the resonant point defined by Z,
care is required to assure that distortion does not occur.
EQ INPUT
8
200Ω
AGC
A13684
• PLL detector APC filter connection. The APC time constant
is switched internally in the IC. When locked, the VCO is
controlled by loop A and the loop gain is reduced. When
unlocked and during weak field reception, the VCO is
9
APC FILTER
controlled by loop B and the loop gain is increased.
For this APC filter we recommend:
R = 150 to 390 Ω
C = 0.47 µF
FROM
APC DET
A
1kΩ 1kΩ 1kΩ
B
9
R
C
+
A13685
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