參數(shù)資料
型號(hào)： STV0196
廠商： 意法半導(dǎo)體
英文描述： QPSK/BPSK DEMODULATOR AND FEC IC
中文描述： 調(diào)制/ BPSK調(diào)制解調(diào)器和FEC集成電路
文件頁(yè)數(shù)： 10/23頁(yè)
文件大?。?/td> 236K
代理商： STV0196
V - CARRIER RECOVERY ; DEROTATOR
The input of the circuit is a pair of demodulated
signals ; however, there may subsist some phase
error not correctedby the front end loop.
Furthermore, the demodulation may be done at
constant frequency; the tuner is trimmed in order
to make the useful signal bandwidth centered on
this demodulationfrequency;inthatcase,acarrier
offsetfrequencymay subsist;itisfixedbythemean
of the on-chipderotator which actsas afine tuning
carrierloop.
The derotator frequency range is limited to an
intervalcorresponding to
±
F
s
/16.
V.1 - Loop Parameters
Like the timing loop, the carrier loop is a second
order systemwhere two parameters
α
and
β
may
be programmed respectively with alpha_car and
beta_car.
Carrier Loop ParameterRegisters
InternalAddress : Hex0E
1
0
1
0
0
0
1
1
D
O
alpha_carrier
beta_carrier
Derotator Frequency Register
InternalAddress : Hex0F
Signed number
This 8 bit R/W register may be written at any time
to force the central frequency of the derotator to
start the carrier research,or read, when theloopis
locked,in order to know the current carrier offset
(one LSBcorrespond to F
s
/2048).
V.2 - Loop Equations
The naturalpulsationis :
ω
n
=
10
3
f
s
√
and the dampingfactor is :
ξ =
0.128
2
alpha_car
√
m
2
m
2
beta_car
.
wheremis thereferencevalue(seeAGCregisters).
The next table gives for the nominal amplitude
m = 24 the natural period (in symbols), and the
dampingfactorforthepossiblevaluesofalpha_car.
Asanexample,thecorrespondingnaturalfrequency
isgivenassumingasymbolfrequencyof20MBauds.
The shaded area correspond to the reset values.
beta_car
(reg. value)
T
=2
π
/
ω
n
(symb per)
f
(kHz) for
F = 20Mbd
alpha_car
(reg. value)
0
1
2
3
4
5
6
7
NA
907
642
454
321
227
160
113
22
31
44
62
88
125
177
Damping Factor
0
1
2
3
4
5
NA
NA
NA
NA
NA
NA 14.18 10.03 7.09
NA
0.89
1.77
3.54
7.09
NA
0.63
1.25
2.51
5.01
NA
0.44
0.89
1.77
3.54
NA
0.31 0.22 0.16
0.63 0.44 0.31
1.25 0.89 0.63
2.51 1.77 1.25
5.01 3.54 2.51
NA
NA
NA
0.11
0.22
0.44
0.89
1.77
VI - CARRIER OFFSET EVALUATOR
An 8 bit register may be read at any time; it gives
a signed value proportionnal to the carrier fre-
quencyoffset accordingto theexpression :
f = 1.8 . 10
-6
. m
2
. N . F
s
(in mode A)
where F
s
is the symbol frequency, m the symbol
module (AGC reference), N the read value.
The maximum value for N is reached in nominal
conditions for a carrier offset of 16% of F
s
; if
greater, N remains saturated,givinga reliable sign
indication overmore than
±
50% F
s
range.
CarrierOffset Register
InternalAddress : Hex10
Signed number
VI.1 - Lock Indicator
This 1 bit Carrier Found flag may be read (see
ViterbiStatusregister)at anytime ; it indicatesthat
a QPSKsignalis found, and thatthe carrier loop is
closed;Thisflagallows todetectfalselockthatcan
happenif theloop bandwidthissmall regardingthe
frequency offset.
VII - CARRIER TO NOISE INDICATOR
InternalAddress : Hex14. Read only register.
b7
b6
b5
b4
b3
b2
b1
b0
This register can be used to estimatethe carrier to
noise level (Eb/No) in a range from 4 to 16dB.
The registervalue dependson both theAGCrefer-
ence level ”m” (see paragraphVIII)and the control
bits”SN[1..0]” (seeparagraphIX).Formore details
about how to use this register, please refer to the
Annexe1.
FUNCTIONAL DESCRIPTION
(continued)
STV0196B
10/23
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