AK8850 Datasheet, PDF (39/99 Pages) Asahi Kasei Microsystems – NTSC Digital Video Decoder

ASAHI KASEI
[AK8850]
7-2-3 PGA ( PROGRAMMABLE GAIN AMP )
A Programmable Gain Amp ( PGA ) to adjust input signals to their proper levels.
The gain range of the PGA is from 0 dB to 12 dB with the gain step of 0.1 dB / step ( 127 steps ).When the AGC function
is enabled,PGA1 / PGA 2 / PGA 3 are properly gain set by digital control. AGC function is disabled by default and the
gain of each PGA is independently set via registers.
PGA Control Register description:
To manually control the PGA, the AGC function is turned off by the [ CONTROL 1 REGISTER ]. The AGC function is
disabled by default.
* [ CONTROL 1 REGISTER ]
bit 7
bit 6
FRCSYNC Reserved
1
0
bit 5
INTPOL[1]
0
bit 4
bit 3
INTPOL[0] AGCC1
Default Value
0
0
bit 2
AGCC0
0
bit 1
AGCT1
0
bit 0
AGCT0
0
to the AGC must be disabled in order to set PGA manually. The setting is done as follows : i.e., set [ AGCT 1 : AGCT 0 ]
= [ 0,0 ].
[AGCT1:AGCT0](bit-1:bit-0)
AGC Function
[0,0]
Disable (Default)
[0,1]
T=1Field
[1,0]
T=7Field
[1,1]
T=29Field
For further details of AGC function, please refer to the AGC description section.
* [ PGA 1 /2 /3 GAIN CONTROL REGISTER ]
bit 7
bit 6
bit 5
Reserved PGA1/2/3[6] PGA1/2/3[5]
0
1
0
bit 4
bit 3
PGA1/2/3[4] PGA1/2/3[3]
Default Value
0
0
bit 2
PGA1/2/3[2]
0
bit 1
PGA1/2/3[1]
0
bit 0
PGA1/2/3[0]
0
Registers for setting the PGA gain values are [ PGA 1 / 2 / 3 GAIN CONTROL REGISTER ]. Each PGA has a
corresponding register. [ PGA 1 GAIN CONTROL REGISTER ] example is shown here.
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
Reserved
PGA1[6]
PGA1[5]
PGA1[4]
PGA1[3]
PGA1[2]
PGA1[1]
PGA1[0]
Default Value
0
1
0
0
0
0
0
0
Each value set by PGA 1 / 2 / 3 [ 6 : 0 ]-bit uses 0.1 dB / step increments. The default gain is set to approximately 6 dB
( PGA 1 /2 / 3 [ 6 : 0 ]= 0x40 ).
Rev.0
39
2002/01