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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： | 26/37页 |
| 文件大小： | 497K |
| 代理商： | AT76C651 |
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AT76C651
26
Timing Recovery
TIMLOOPCFG: 0x23 to 0x24 (read/write)
These two registers configure the loop bandwidth of the
timing recovery loop.
b7
b6
b5
b4
Example:
0x7F for register 0x23 and 0x9 for register 0x24
The three parameters blmax_mexp, blmin_mexp and
bltrack_mexp are 4-bit unsigned numbers that must follow
the conditions:
7
≤
blmax_mexp
≤
blmin_mexp
≤
15
7
≤
bltrack_mexp
≤
15
They are related to the bandwidth blmax, blmin and bltrack
by the formula:
blx
=
blmax is the maximal and initial bandwidth value used with
a robust (Gardner type) comparator. blmin is the minimal
bandwidth value that can be taken by the loop bandwidth
with the same comparator. When blmax > blmin, the loop
can automatically decrease when the lock indicator is posi-
tive or increase when this signal detects that the timing
recovery system is out of lock. This variable bandwidth
allows fast convergence, large timing frequency lock-in
range in initial acquisitio1
n phase and low timing jitter when the system is locked.
bltrack is the fixed value of the bandwidth used with deci-
sion base comparator. Typical values corresponding to the
example above are:
blmax = 2
-7
blmax_mexp = 7
blmin = 2
-15
blmin_mexp = 15
bltrack = 2
-9
bltrack_mexp = 9
TIMLOOPMONIT: 0x29 (read)
This monitoring register indicates the value of the automat-
ically variable loop bandwidth.
b7
b6
b5
b4
Bandwidth Bl, which is given by formula:
Bl
=
Bl_mexp is an unsigned value, taking values from
blmax_mexp to blmin_mexp (see TIMLOOPCFG).
When timing is well recovered, Bl is equal to blmin.
Carrier Recovery
CARALPHAACQ/CARBETAACQ: 0x31/0x32 (read/write)
These two registers select the carrier loop bandwidth dur-
ing acquisition phase. Through those 2 bytes one can
control the bandwidth and the damping factor (
ξ)
of the
loop filter.
Table 14 depicts some typical values for CARALPHAACQ
and CARBETAACQ.
In automatic configuration, these parameters correspond to
Bl f
symbol
= 0.03 and
ξ
= 1.0.
CARALPHATRACK/CARBETATRACK: 0x33/0x34
(read/write)
These two registers select the carrier loop bandwidth dur-
ing tracking phase (after acquisition). The same table as
given for (0x31/0x32) configures these parameters. The
switch between tracking phase and acquisition phase takes
place when agc2, equalizer and carrier are locked.
b7
b6
b5
b4
In automatic configuration, these parameters correspond to
Bl f
symbol
= 0.03 and
ξ
= 4.0.
blmax_mexp
0x23
bltrack_mexp
0x24
b3
b2
b1
b0
reserved
blmin_mexp
2
-Blx_mexp
Bl_mexp
0x29
b3
b2
b1
b0
reserved
2
-Bl_mexp
Table 14.
B
l
f
symbol
ξ
CARALPHAACQ
CARBETAACQ
0.005
0.7
0xAE
0x9C
0.005
1.0
0x98
0x98
0.005
2.0
0x9A
0xBC
0.005
4.0
0x9A
0xDD
0.010
0.7
0x9E
0x7C
0.010
1.0
0x88
0x78
0.010
2.0
0x8A
0x9C
0.010
4.0
0x8A
0xBD
0.030
0.7
0x7A
0x4D
0.030
1.0
0x7C
0x49
0.030
2.0
0x7E
0x6D
0.030
4.0
0x7F
0x8E
0x31
0x32
b7
b6
b5
b4
b3
b2
b1
b0
carbetaacq
caralphaacq
caralphatrack
0x33
0x34
b3
b2
b1
b0
carbetatrack
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