STV8203 ST Microelectronics, STV8203 Datasheet - Page 22

• Manufacturer Part Number: STV8203
• Description: MULTISTANDARD TV SOUND DEMODULATOR
• Manufacturer: ST Microelectronics

STV8203
PROGRAMMING THE DEVICE (continued)
AGCS (AGC Control and Status for ADC)
Address
Type
Reset
AGC-ERR : Gain Control Signal of amplifier before ADC. There are 32 steps of 1.25dB.
SIG-OVR
SIG-UND
IAGCR (Internal AGC Reference for QPSK)
Address
Type
Reset
Sets the mean value of the internal AGC, used for QPSK demodulation. The default setting corresponds
to half full scale amplitude at the PLL input.
IAGCC (Internal AGC Time Constant for QPSK)
Address
Type
Reset
IAGC-OFF : 1 = Internal agc = off
IAGC-CST : Internal AGC Programmable Step Constant.
22/31
IAGC-OFF
bit 7
bit 7
bit 7
0
: 1 = agc overloaded - signal too BIG
: 12
: R/W
: 0100 00XX
When AGC_CMD = 0, AGC-ERR can be read thus indicating the input level. It can also be
written to thus presetting the AGC level which will then adjust itself to the final value. When
AGC_CMD = 1, the AGC is off and thus writing to AGC-ERR directly controls the AGC
amplifier gain. Reading AGC_ERR just confirms the fixed value.
1 = agc under loaded - signal too SMALL
When the AGC is in automatic mode (agc_cmd=0), bit 0 indicates if the input signal is too
small and bit 1 if the AGC is too big. These bits could be used when setting the input level
to the STV8203.
: 14
: R/W
: 1000 1000
: 15
: R/W
: 0000 0011
Only enabled when AUTOSTANDARD is off. Normally , the internal AGC should be OFF for
FM and ON for QPSK.
This bit is controlled by AUTOSTANDARD when this function is activated.
Set the internal AGC time constant; the compromise is between fast settling time (for the
quickest Nicam identification) and noise immunity. The control range is about 45dB divided
into 0.2dB steps. These bits control the time per step (values given for QPSK mode) :
AGC-ERR [6:2]
bit 6
bit 6
bit 6
0
00000
00001
11110
11111
AGC-CST [2:0]
.....
000
001
111
.....
bit 5
bit 5
bit 5
0
AGC-ERR
bit 4
bit 4
bit 4
0
IAGC-REF
Step time ( s)
bit 3
bit 3
bit 3
703
352
.....
5.5
0
Gain (dB)
37.50
38.75
1.25
.....
0
bit 2
bit 2
bit 2
Time Response (ms)
IAGC-CST
SIG-OVR
bit 1
bit 1
bit 1
0.82
105
.....
53
SIG-UND
bit 0
bit 0
bit 0