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参数资料
| 型号： | AT76C651 |
| 厂商： | ATMEL CORP |
| 元件分类： | 消费家电 |
| 英文描述： | Digital Reception/Transmission Integrated DVB compliant QAM Demodulator(兼容DVB的正交振幅调制解调电路) |
| 中文描述： | SPECIALTY CONSUMER CIRCUIT, PQFP100 |
| 封装： | TQFP-100 |
| 文件页数： | 32/37页 |
| 文件大小： | 497K |
| 代理商： | AT76C651 |
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AT76C651
32
DDSFREQOFFSET: 0x89 to 0x8A (read)
This monitoring register indicates the frequency offset
recovered by the DDS (at IF to BB down conversion). This
value, added to the frequency entered in register BBFREQ,
gives the corrected IF frequency of the input signal.
This value is a fraction of the crystal frequency f
XTAL
.
b7
b6
b5
b4
The offset frequency is given by:
CARFREQOFFSET: 0x8B to 0x8C (read)
This monitoring register indicates the frequency offset
recovered by the carrier. The collected value is normalized
to symbol rate.
b7
b6
b5
b4
Address 0x8B (MSBs) must be read from the device first in
order to ensure the correctness of the content of 0x8C
(LSBs). The offset frequency is given by:
The total frequency offset recovered is given by:
f
f
DDSFREQOFFSET
=
PHASENOISE: 0x8D to 0x8E (read)
The residual phase noise (after carrier recovery) is esti-
mated. The collected information contains the phase noise
due to oscillators and also the phase noise due to the addi-
tive noise integrated by the carrier loop filter. Below is an
explanation of how to compute the total residual phase
noise and how to extract the phase noise due to additive
noise.
b7
b6
b5
b4
In the following formula:
denotes the residual phase noise and
σ
2
the mean of
squared.
The parameter A depends on the QAM format and is given
Table 19:
The phase noise portion due to the integration of the addi-
tive noise by the loop filter is given by:
The parameter
α
depends of the QAM format and is given
by the table below.
σ
2
denotes the mean square of the
additive noise description (see
“
ADDITIVENOISE: 0x8F to
0x90 (read)
”
on page 33), and B
l
the selected carrier loop
bandwidth for tracking phase.
The residual phase noise due to oscillator impairments is
then equal to:
Using
σ
2
osc
, the configured loop bandwidth, the symbol
rate and an assumption about the tuner phase noise shap-
ing, an estimate of the phase noise at a given frequency
offset can be obtained.
0x89
0x8A
b3
b2
b1
b0
ddsfreqoffset (7:0)
ddsfreqoffset (15:8)
f
DDSFREQOFFSET
ddsfreqoffset
-------------------------------------------------------
f
×
2
20
=
0x8B
0x8C
b3
b2
b1
b0
carfreqoffset (7:0)
carfreqoffset (15:8)
f
CARFREQOFFSET
signed carfreqoffset
--------------------------------------------------------------------------------
)
f
×
2
17
=
f
CARFREQOFFSET
+
0x8D
0x8E
b3
b2
b1
b0
phasenoise (7:0)
phasenoise (15:8)
Table 19.
QAM
A (dB)
QPSK
-45.15
QAM-16
-54.69
QAM-32
-54.69
QAM-64
-62.05
QAM-128
-62.05
QAM-256
-68.67
QAM-512
-68.67
QAM-1024
-74.98
Table 20.
QAM
α
QPSK
2.53e-2
QAM-16 to QAM-1024
2.83e-2
σ
2
dB
(
)
A dB
)
10
10
phasenoise
(
)
log
×
(
)
+
=
σ
2
n
B
l
σ
2
n
α
×
×
=
σ
2
osc
σ
2
σ
2
n
–
=
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