STA002 datasheet(20/43 Pages) STMICROELECTRONICS

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AGC1 integrator value register (AGC1_INTG)

Internal address: 85 H

Reset Value: 00H

MSB

LSB

signed number

To open the AGC1 loop this register must be re-

set and the AGC1_BETA parameter must be

"111".

3.6. AGC2

3.6.1 AGC2 control

The AGC2 loop is used at the output of the

Nyquist / interpolator filter for power optimization

in the signal bandwith.

The modulus of the complex signal at the output

of the Nyquist filter is compared to a programma-

ble

threshold

and

then

scaled

the

AGC2_BETA coefficient and integrated.

The integrated error drives two multiplier at the

output of both the Nyquist filters in order to man-

tain constant the level signal at the demodulator

output.

3.6.2 Register

AGC2 reference level register (AGC2_REF)

Internal address: 86 H

Reset Value : 16 H

MSB

LSB

AGC2_REF

The value written in this register corresponds to

the modulud of the output complex signal (I,Q).

AGC2 integrator gain register (AGC2_BETA)

Internal address: 87 H

Reset Value: 00H

MSB

LSB

XXXXX

AGC2_BETA

The AGC2 loop gain

βAGC2 can be controlled by

this register:

βAGC2 = 2AGC2_BETA

The parameter AGC2_BETA can take values

from 0 to 6. When AGC2_BETA is set to "111"

the loop gain is null and the AGC2 amplifier gain

keeps the last value.

AGC2 integrator value register (AGC2_INTG)

Internal address: 88 H

Reset Value: 00H

MSB

LSB

signed number

To open the AGC2 loop this register must be re-

set and the AGC2_BETA parameter must be

"111".

The AGC2 reference level value impacts the

value of the following functions:

- Carrier to Noise indicator;

- The carrier loop;

- The timing loop

3.7. LOCK INDICATOR

This 1 bit carrier lock flag may be read at any

time.

This flag is available at the chip output and can

be also read by the micro in the FLAG register

A low logic level at the Lock Indicator means that

a QPSK signal is found.The lock indicator flag

controls , internally, the ramp block. The sweep

function is disable whenever a lock condition is

detected.

3.8. CARRIER TO NOISE INDICATOR

A register is used to estimate the carrier to noise

level C/N in a range from 4 to 17dB.

Remark: in the WorldStar system the correspon-

dence between C/N, Eb/No (Energy per net-bit to

noise ratio) and Eb/No|QPSK (Energy per channel-

bit to noise ratio) are the following:

C/N = Eb/No|QPSK + 3dB = Eb/No - 0.6dB

The C/N indicator may be used to optimize the

antenna pointing or to give an idea of the RF si-

gal quality. This is based on the measure of the

scattering of the QPSK constellation: a 10 bit

counter is incremented when the scattering is ex-

ceeding a certain value. After a programmable

time interval the 8MSB of the counter are loaded

in the corresponding I

2C-bus register.

The register value strongly depends on the

AGC2_REF parameter.

3.8.1 C/N Register (CNCNT)

This register contains a value proportional to the

signal to noise ratio at the Nyquist filter output

(Eb/No|QPSK).

STA002

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