AGCS (AGC Control and Status for ADC)

Address

: 12

Type

: R/W

Reset

: 0100 00XX

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

0

AGC-ERR

SIG-OVR

SIG-UND

AGC-ERR : Gain Control Signal of amplifier before ADC. There are 32 steps of 1.25dB.

AGC-ERR [6:2]

Gain (dB)

00000

0

00001

1.25

.....

.....

11110

37.50

11111

38.75

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.

SIG-OVR

SIG-UND

: 1 = agc overloaded - signal too BIG

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.

IAGCR (Internal AGC Reference for QPSK)

Address

: 14

Type

: R/W

Reset

: 1000 1000

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

IAGC-REF

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

: 15

Type

: R/W

Reset

: 0000 0011

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

IAGC-OFF

0000

IAGC-CST

IAGC-OFF : 1 = Internal agc = off

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.

IAGC-CST : Internal AGC Programmable Step Constant.

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-CST [2:0]

Step time (

µs)

Time Response (ms)

000

703

105

001

352

53

.....

.....

.....

111

5.5

0.82

PROGRAMMING THE DEVICE (continued)

STV8203

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