Continued from preceding page.
Pin No.
Pin
LA75675M-S
Function
Equivalent circuit
40 kΩ
Equalizer circuit
This circuit corrects the frequency characteristics of
the video signal.
2.2 kΩ
1 kΩ
6
EQ OUTPUT
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.
6
• Using the equalizer amplifier
7
EQ amp
If the input signal is vi and the output signal vo, then
8
R1
—— +1 (Vi + Vin) = Vo × G
Z
G: Gain of the voltage follower amplifier
7
C
L =Z
R
A12623
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 kΩ 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.
EQ INPUT
8
200 Ω
AGC
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
9
APC filter
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.
FROM
APC DET
A
1 kΩ 1 kΩ 1 kΩ
B
9
R
C
+
A12625
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No. 6276-8/13