(2) Working principle: this tuner includes middle frequency amplifying circuit, which adopts IIC bus
means to perform function control (such as select channel and search channel) through MST718 built-in
MCU. After high frequency signals are modulated, video signals and audio signals are separated
through being filtered by internal filter of tuner. Audio and video signals output from pin 12, 14 and then
send to audio and video processing circuit. When tuner receives NICAM signal, NICAM signals output
From pin 11 of tuner to STV8216 for modulating.
(3) Tuner pin function is shown in the following table:
2. TV Tuner circuit
(1) Tuner circuit is shown in the figure 3.2.4.1
Figure 3.2.4.1 Tuner circuit diagram
- 28 -
Pin
Name
Function
Pin
Name
Function
1
NC
NC
8
NC
DVB input jack is unus ed
2
VT
Connect with external power
9
NC
NC
3
VS
(+)5V power supply pin
10
NC
NC
4
SCL
SCLis connected with MCU
11
SIF
SIOMAD
5
SDA
SDA is connected with MCU
12
TUNER_CVBS
Video output
6
AS
AGC control end is unused
13
VIF
5V power is connected
externally
7
AFC
DVB input jack is unus ed
14
AUDIO
Audio output