
AD9853
–5–
REV. C
Table I. Modulator Function Description
Modulation Encoding Format
FSK*, QPSK, DQPSK, 16-QAM, D16-QAM, Selectable via Control Bus
Output Carrier Frequency Range
DC – 63 MHz with +3.3 V Supply Voltage
DC – 84 MHz with +5 V Supply Voltage
Serial Input Data Rate
Evenly Divisible Fraction of Reference Clock
Pulse-Shaping FIR Filter
41 Tap, Linear Phase, 10-Bit Coefficients Fully Programmable via Control Bus
Interpolation Rate
= (4/
M
)
×
(
ICIC
1)
×
(
ICIC
2) where:
M
= 2 for QPSK,
M
= 4 for 16-QAM
Minimum and Maximum Rates
Minimum Interpolation Rate—QPSK = 2
×
3
×
2 = 12
16-QAM = 1
×
4
×
3 = 12
Maximum Interpolation Rate—QPSK = 2
×
31
×
63 = 3906
16-QAM = 1
×
31
×
63 = 1953
These are the minimum and maximum interpolation ratios from the input data rate to the
system clock. The interpolation range is a function of the fixed interpolation factor of four
in the FIR filters, the programmed CIC filter interpolation rates (ICIC1, ICIC2), as well
as system timing constraints.
+3.3 V Supply: 21 MHz with 6
×
REFCLK enabled, 126 MHz with 6
×
REFCLK disabled
+5 V Supply: 28 MHz with 6
×
REFCLK enabled, 168 MHz with 6
×
REFCLK disabled
Fixed 6
×
reference clock multiplier, enable/disable control via control bus
Interpolation Range
Maximum Reference Clock Frequency
6
×
REFCLK
R-S FEC
Enable/disable via control bus and dedicated control pin. Control pin enable/disable function:
Logic “1” = Enable
Logic “0” = Disable
Primitive Polynomial: p(x) = x
8
+ x
4
+ x
3
+ x
2
+ 1
Code Generator Polynomial: g(x) = (x +
α
0
)(x +
α
1
)(x +
α
2
) . . . (x +
α
2t –1
)
Selectable via Control Bus
t = 0–10 (Programmable)
Codeword Length (N) = 255 max (Programmable)
N = K + 2 t (K Range = 16
≤
K
≤
255 – 2 t)
FEC/Randomizer can be transposed in signal chain via control bus.
I
×
COS + Q
×
SIN (default) or I
×
COS – Q
×
SIN, selectable via control bus.
I/Q Channel Spectrum
Preamble Insertion
0–96 Bits, Programmable Length and Content
Randomizer
Enable/Disable Control via Control Bus
Generating Polynomial:
x
6
+ x
5
+ 1, Programmable Seed (Davic/DVB-Compliant)
or
x
15
+ x
14
+ 1, Programmable Seed (DOCSIS-Compliant)
Randomizer and FEC blocks can be transposed in signal chain, via control bus.
*In FSK mode, F0:F1 are direct DDS Cosine output. The two interpolator stages of the AD9853 are not used in the FSK mode and should be programmed for
maximum interpolation rates to reduce unnecessary current consumption. This means that Interpolator #1 should be set to a decimal value of 31, and Interpolator
#2 should be set to decimal value of 63. This is easily accomplished by programming Registers 12 and 13 (hex) with the values of FF (hex).