Technical Note of LA76818
2002/01/23
Pin 2 (FM Output)
This is an output pin for FM detector. The output circuit is a voltage follower.
The DC voltage is about 2.5V and the dynamic range is 4V.
The setting of BUS is depending on the frequency of SIF:
SIF frequency
BUS setting
4.5MHz
‘00’
5.5MHz
’01’
6.0MHz
‘10’
6.5MHz
‘11’
The output level is variable which is controlled by BUS:
BUS setting for FM Gain
Output level
‘0’
1000mVrms (±50KHz)
‘1’
1000mVrms (±25KHz)
The output impedance is variable which is controlled by BUS:
BUS setting for Deem-TC
Output Impedance
‘0’
5.0KΩ
‘1’
7.5KΩ
The time constant of the de-emphasis is determined by the value of external
capacity (0.01uF). There is no necessary to connect an external capacity if a stereo IC
is used. But, the output impedance is very high. This pin is also used to be an internal
pin for audio SW.
2
2K
300u
R1(PAL)
R2(NT)
300u
300
FM 檢波信號
Audio
SW
BUS:Deem-TC
50u
The circumference circuit of pin 2
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