参数资料
| 型号： | AD6623ASZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 20/48页 |
| 文件大小： | 0K |
| 描述： | IC TSP 4CHAN 104MSPS 128MQFP |
| 标准包装： | 1 |
| 应用： | 传输信息处理器 |
| 接口： | 串行 |
| 封装/外壳： | 128-BFQFP |
| 供应商设备封装： | 128-MQFP（14x20） |
| 包装： | 托盘 |
| 安装类型： | 表面贴装 |
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REV. A
AD6623
–27–
In the complex mode, the NCO serves as a quadrature local oscillator
running at fCLK/2 capable of producing any frequency step between
–fCLK/4 and +fCLK/4 with a resolution of fCLK/2
33 (0.0121 Hz for
fCLK = 104 MHz).
In the real mode, the NCO serves as a quadrature local oscillator
running at fCLK capable of producing any frequency step between
–fCLK/2 and +fCLK/2 with a resolution of fCLK/2
32 (0.0242 Hz for
fCLK = 104 MHz). The quadrature portion of the output is
discarded. Negative frequencies are distinguished from positive
frequencies solely by spectral inversion. The digital IF is calculated
using the equation:
ff
NCO
frequency
IF
NCO
=×
_
2
32
(22)
where:
NCO_frequency is the decimal equivalent of the 32-bit binary
value written to 0xn02,
fIF is the desired intermediate frequency (in Hz), and
fNCO is fCLK/2 (in Hz) for complex outputs and fCLK (in Hz)
for real outputs.
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
th bit, then phase dither has no effect.
If the fraction below the 18
th bit is near a 1/2 or 1/3 of the 18th
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
32
Q
D
PN
GEN.
NCO
FREQUENCY
WORD
16
PHASE
OFFSET
16
32
Q
D
ANGLE TO
CARTESIAN
CONVERSION
PN
GEN.
I DATA FROM
CIC5
Q DATA FROM
CIC5
I
Q
I, Q
CLK
ON
OFF
ON
OFF
32
MICROPROCESSOR
INTERFACE
Figure 33. Numerically Controlled Oscillator and QAM Mixer
Table XIV. Maximum Bandwidth of Rejection for LrCIC2 Values
LrCIC2
–110 dB
–100 dB
–90 dB
–80 dB
–70 dB
1
Full
2
0.0023
0.0040
0.0072
0.0127
0.0226
3
0.0029
0.0052
0.0093
0.0165
0.0292
4
0.0032
0.0057
0.0101
0.0179
0.0316
5
0.0033
0.0059
0.0105
0.0186
0.0328
6
0.0034
0.0060
0.0107
0.0189
0.0334
7
0.0034
0.0061
0.0108
0.0192
0.0338
8
0.0035
0.0062
0.0109
0.0193
0.0341
9
0.0035
0.0062
0.0110
0.0194
0.0343
10
0.0035
0.0062
0.0110
0.0195
0.0344
11
0.0035
0.0062
0.0110
0.0195
0.0345
12
0.0035
0.0062
0.0111
0.0196
0.0346
13
0.0035
0.0062
0.0111
0.0196
0.0346
14
0.0035
0.0063
0.0111
0.0196
0.0346
15
0.0035
0.0063
0.0111
0.0197
0.0347
16
0.0035
0.0063
0.0111
0.0197
0.0347
17
0.0035
0.0063
0.0111
0.0197
0.0347
18
0.0035
0.0063
0.0111
0.0197
0.0348
19
0.0035
0.0063
0.0111
0.0197
0.0348
20
0.0035
0.0063
0.0111
0.0197
0.0348
21
0.0035
0.0063
0.0111
0.0197
0.0348
22
0.0035
0.0063
0.0111
0.0197
0.0348
23
0.0035
0.0063
0.0111
0.0197
0.0348
24
0.0035
0.0063
0.0112
0.0197
0.0348
25
0.0035
0.0063
0.0112
0.0198
0.0348
26
0.0035
0.0063
0.0112
0.0198
0.0349
27
0.0035
0.0063
0.0112
0.0198
0.0349
28
0.0035
0.0063
0.0112
0.0198
0.0349
29
0.0035
0.0063
0.0112
0.0198
0.0349
30
0.0035
0.0063
0.0112
0.0198
0.0349
31
0.0035
0.0063
0.0112
0.0198
0.0349
32
0.0035
0.0063
0.0112
0.0198
0.0349
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.
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