sta002 STMicroelectronics, sta002 Datasheet - Page 20

• Manufacturer Part Number: sta002
• Description: Starmano Channel Decoder
• Manufacturer: STMicroelectronics

STA002
AGC1 integrator value register (AGC1_INTG)
Internal address: 85 H
Reset Value: 00H
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
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
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
AGC2_BETA
The AGC2 loop gain
this register:
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.
20/43
MSB
MSB
MSB
b7
X
X
threshold
b6
X
X
b5
b5
X
AGC2
signed number
and
b4
b4
X
= 2
AGC2
then
AGC2_BETA
b3
b3
X
can be controlled by
scaled
b2
b2
b2
b1
b1
b1
by
LSB
LSB
LSB
b0
b0
b0
the
bit to noise ratio) are the following:
AGC2 integrator value register (AGC2_INTG)
Internal address: 88 H
Reset Value: 00H
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|
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
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|
MSB
b7
C/N = Eb/No|
QPSK
b6
).
b5
QPSK
signed number
b4
2
C-bus register.
+ 3dB = Eb/No - 0.6dB
QPSK
b3
(Energy per channel-
b2
b1
LSB
b0