AD6623ABC Analog Devices Inc, AD6623ABC Datasheet - Page 27

• Manufacturer Part Number: AD6623ABC
• Description: IC TX SGNL PROCESS QUAD 196CSPBA
• Manufacturer: Analog Devices Inc

Specifications of AD6623ABC

• Rohs Status: RoHS non-compliant
• Applications: Transmit Signal Processor
• Interface: Serial
• Package / Case: 196-CSPBGA
• Mounting Type: Surface Mount
• Voltage - Supply: -

Table XIV. Maximum Bandwidth of Rejection for L
L
NUMERICALLY CONTROLLED OSCILLATOR/TUNER (NCO)
Each channel has a fully independent tuner. The tuner accepts
data from the CIC filter, tunes it to a digital Intermediate
Frequency (IF), and passes the result to a shared summation block.
The tuner consists of a 32-bit quadrature NCO and a Quadrature
Amplitude Mixer (QAM). The NCO serves as a local oscillator and
the QAM translates the interpolated channel data from baseband
to the NCO frequency. The worst case spurious signal from the
NCO is better than –100 dBc for all output frequencies. The tuner
can produce real or complex outputs as requested by the shared
summation block.
REV. A
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
rCIC2
1
2
3
4
5
6
7
8
9
–110 dB
Full
0.0023
0.0029
0.0032
0.0033
0.0034
0.0034
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
MICROPROCESSOR
–100 dB
Full
0.0040
0.0052
0.0057
0.0059
0.0060
0.0061
0.0062
0.0062
0.0062
0.0062
0.0062
0.0062
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
INTERFACE
Figure 33. Numerically Controlled Oscillator and QAM Mixer
–90 dB
Full
0.0072
0.0093
0.0101
0.0105
0.0107
0.0108
0.0109
0.0110
0.0110
0.0110
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0112
0.0112
0.0112
0.0112
0.0112
0.0112
0.0112
0.0112
0.0112
FREQUENCY
16
32
OFFSET
PHASE
WORD
NCO
D
Q
–80 dB
Full
0.0127
0.0165
0.0179
0.0186
0.0189
0.0192
0.0193
0.0194
0.0195
0.0195
0.0196
0.0196
0.0196
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0198
0.0198
0.0198
0.0198
0.0198
0.0198
0.0198
0.0198
32
16
CLK
rCIC2
32
D
–70 dB
Full
0.0226
0.0292
0.0316
0.0328
0.0334
0.0338
0.0341
0.0343
0.0344
0.0345
0.0346
0.0346
0.0346
0.0347
0.0347
0.0347
0.0348
0.0348
0.0348
0.0348
0.0348
0.0348
0.0348
0.0348
0.0349
0.0349
0.0349
0.0349
0.0349
0.0349
0.0349
Values
Q
32
OFF
ON
32
–27–
In the complex mode, the NCO serves as a quadrature local oscillator
running at f
–f
f
In the real mode, the NCO serves as a quadrature local oscillator
running at f
–f
f
discarded. Negative frequencies are distinguished from positive
frequencies solely by spectral inversion. The digital IF is calculated
using the equation:
where:
Phase Dither
The AD6623 provides a phase dither option for improving the
spurious performance of the NCO. Phase dither is enabled by
writing a “1” to Bit 3 of Channel Register 0xn01. When phase
dither is enabled, spurs due to phase truncation in the NCO are
randomized. The choice of whether phase dither is used in a system
will ultimately be decided by the system goals and the choice of IF
frequency. The 18 most significant bits of the phase accumulator
are used by the angle to Cartesian conversion. If the NCO frequency
has all zeroes below the 18
If the fraction below the 18
bit, then spurs will accumulate separated from the IF by 1/2 or
1/3 of the CLK frequency. The smaller the denominator of this
residual fraction, the larger the spurs due to phase truncation will
be. If the phase truncation spurs are unacceptably high for a given
frequency, then the phase dither can reduce these at the penalty
of a slight elevation in total error energy. If the phase truncation
spurs are small, then phase dither will not be effective in reducing
them further, but a slight elevation in total error energy will occur.
Amplitude Dither
Amplitude dither can also be used to improve spurious performance
of the NCO. Amplitude dither is enabled by writing a “1” to Bit 4
of Channel Register at 0xn01. When enabled, amplitude dither
can reduce spurs due to truncation at the input to the QAM. If
the entire frequency word is close to a fraction that has a small
GEN.
CLK
CLK
PN
CLK
CLK
NCO_frequency is the decimal equivalent of the 32-bit binary
value written to 0xn02,
f
f
for real outputs.
IF
NCO
f
IF
32
= 104 MHz).
= 104 MHz). The quadrature portion of the output is
is the desired intermediate frequency (in Hz), and
/4 and +f
/2 and +f
=
is f
CONVERSION
CARTESIAN
ANGLE TO
f
NCO
CLK
CLK
CLK
/2 (in Hz) for complex outputs and f
×
OFF
/2 capable of producing any frequency step between
CLK
CLK
ON
capable of producing any frequency step between
NCO frequency
/4 with a resolution of f
/2 with a resolution of f
GEN.
PN
_
2
32
I, Q
th
th
Q DATA FROM
I DATA FROM
bit, then phase dither has no effect.
bit is near a 1/2 or 1/3 of the 18
CIC5
CIC5
CLK
CLK
Q
I
/2
/2
33
32
AD6623
(0.0121 Hz for
(0.0242 Hz for
CLK
(in Hz)
(22)
th