- 您现在的位置：买卖IC网 > PDF目录373890 > AD6622 (Analog Devices, Inc.) Four-Channel, 75 MSPS Digital Transmit Signal Processor TSP PDF资料下载
参数资料
| 型号： | AD6622 |
| 厂商： | Analog Devices, Inc. |
| 英文描述： | Four-Channel, 75 MSPS Digital Transmit Signal Processor TSP |
| 中文描述： | 4通道，75 MSPS的数字传输信号处理器判刑 |
| 文件页数： | 20/28页 |
| 文件大小： | 242K |
| 代理商： | AD6622 |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页第16页第17页第18页第19页当前第20页第21页第22页第23页第24页第25页第26页第27页第28页
AD6622
–20–
REV. 0
SCALING
Proper scaling of the wideband output is critical to maximize the
spurious and noise performance of the AD6622. A relatively small
overflow anywhere in the data path can cause the spurious free
dynamic range to drop precipitously. Scaling down the output
levels also reduces dynamic range relative to an approximately
constant noise floor. A well-balanced scaling plan at each point
in the signal path will be rewarded with optimum performance.
The scaling plan can be separated into two parts: multicarrier
scaling and single-carrier scaling.
Multicarrier Scaling
An arbitrary number of AD6622s can be cascaded to create a
composite digital IF with many carriers. As the number of carriers
increases, the peak-to-rms ratio of the composite digital IF will
increase as well. It is possible and bene
fi
cial to limit the peak-to-
rms ratio through careful frequency planning and controlled phase
offsets. Nevertheless, in most cases with a large number of carriers,
the worst-case peak is an unlikely event.
The AD6622 immediately preceding the DAC can be programmed
to clip rather than wrap around (see the Summation Block descrip-
tion). For a large number of carriers, a rare but
fi
nite chance
of clipping at the AD6622 wideband output will result in superior
dynamic range compared to lowering each carrier level until
clipping is impossible. This will also be the case for most DACs.
Through analysis or experimentation, an optimal output level of
individual carriers can be determined for any particular DAC.
Single-Carrier Scaling
Once the optimal power level is determined for each carrier, one
must determine the best way to achieve that level. The maximum
SNR can be achieved by maximizing the intermediate power
level at each processing stage. This can be done by assuming the
proper level at the output and working backwards along the signal
path: Summation, NCO, CIC, and
fi
nally, RCF.
The summation block is intended to combine multiple carriers,
with each carrier at least 6 dB below full scale. For this con
fi
gu-
ration, the AD6622 driving the DAC should have clip detection
enable. OUT17 becomes a clip indicator that reports clipping in
both polarities. If the DAC requires offset binary outputs, the
internal offset binary conversion should be enabled as well. Any
preceding cascaded AD6622s should disable clip detection and
offset binary conversion. The IN17
–
IN0 of the
fi
rst AD6622 in the
cascade should be grounded. See the Summation Block section
for details. In this con
fi
guration, intermediate OUT17s will
serve as guard bits that allow intermediate sums to exceed full
scale. As long as the
fi
nal output does not exceed 6 dB over full
scale, the clip detector will perform correctly.
If a single carrier needs to exceed
–
6 dB full scale, hardwired
scaling can be accomplished according to the table below. This
is most useful when the AD6622 is processing a Single Wide-
band Carrier such as UMTS or CDMA 2000.
Table XI. Output Bit Scaling
M
ax Single-
Carrier Level
–
12.04 dB
–
6.02 dB
0 dB
+6.02 dB
+12.04 dB
+18.06 dB
+24.08 dB
Connect to
DAC MSB
OUT17
OUT16
OUT15
OUT14
OUT13
OUT12
OUT11
Clip
Detect
N/A
±
+Only
+Only
+Only
+Only
+Only
Offset Binary
Compensation
Internal
Internal
0x18000
0x1C000
0x1E000
0x1F000
0x1F800
The NCO/Tuner is equipped with an output scalar that ranges
from
–
6.02 dB to
–
24.08 dB below full scale, in 6.02 dB steps.
See the NCO/Tuner section for details. The best SNR will be
achieved by maximizing the input level to the NCO and using
the largest possible NCO attenuation. For example, to achieve
an output level
–
20 dB below full scale, one should set the CIC
output level to
–
1.94 dB below full scale and attenuate by
–
18.06 dB in the NCO.
The CIC is equipped with an output scalar that ranges from
0 dB to
–
150.51 dB below full scale in 6.02 dB steps. This large
attenuation is necessary to compensate for the potentially large
gains associated with CIC interpolation. See the CIC section for
details. For example to achieve an output level of
–
1.94 dB below
full scale, with a CIC5 interpolation of 27 (114.51 dB gain) and
a CIC2 interpolation of 3 (9.54 dB gain), one should set the
CIC_Scale to 20 and the RCF output level to
–
5.59 dB below
full scale.
–
.
1 94
–
.
–
.
.
–
.
5 59
9 54
114 51
20
6 02
+
×
=
(18)
The RCF is equipped with an output scalar that ranges from 0 dB
to
–
18.06 dB below full scale in 6.02 dB steps. This attenuation
can be used to compensate for
fi
lter gain in the RCF. For example,
if the desired RCF output is
–
5.59 dB and the maxim gain of the
RCF coef
fi
cients is 11.04 dB, then the RCF_Coarse_Scale should
be set to two and the coef
fi
cients should be scaled so that the
largest coef
fi
cient is
–
4.59 dB below full scale. The largest pos-
sible gain of the RCF coef
fi
cients is when the largest coef
fi
cient
of the impulse response is normalized to one. This means that
all of the coef
fi
cients are as large as possible so the sum of the
coef
fi
cients are as large as possible. This maximum gain will
determine the RCF_Coarse_Scale, which should be used to
make the total RCF gain between 0 dB and
–
6.02 dB. After the
RCF_Coarse_Scale is chosen, the coef
fi
cients can be rescaled, as
in the example, to set the total RCF gain to a desired level. See the
RCF section for additional information.
–
.
5 59
–
.
.
–
.
4 59
11 04
2
6 02
+
×
=
(19)
Finally, as described in the RCF section, there may be a worst-
case peak of a phase that is larger than the channel center gain. In
the preceding example, if the worst-case to channel center ratio
is larger than 4.59 dB (potentially overflowing the RCF), the
RCF_Coarse_Scale should be reduced by one and the CIC_Scale
should be increased by one. In the preceding example, if the worst-
case to channel center ratio is larger than 5.59 dB (potentially
overflowing the RCF and CIC), the RCF_Coarse_Scale should be
reduced by one and the NCO_Output_Scale should be increased
by one.
MICROPORT INTERFACE
The Microport interface is the communications port between the
AD6622 and the host controller. There are two modes of bus
operation: Intel Nonmultiplexed Mode (INM), and Motorola
Nonmultiplexed Mode (MNM), which is set by hard wiring the
MODE pin to either ground or supply. The mode is selected
based on the use of the Microport control lines (
DS
or
RD
,
DTACK
or RDY, R/
W
or
WR
) and the capabilities of the host
processor. See the timing diagrams for details on the operation of
both modes.
The External Memory Map provides data and address registers
to read and write the extensive control registers in the Internal
Memory Map. The control registers access global chip functions
and multiple control functions for each independent channel.
相关PDF资料 |
PDF描述 |
|---|---|
| AD6623 | 4-Channel, 104 MSPS Digital Transmit Signal Processor TSP |
| AD6623ABC | 4-Channel, 104 MSPS Digital Transmit Signal Processor TSP |
| AD6623AS | 4-Channel, 104 MSPS Digital Transmit Signal Processor TSP |
| AD6623PCB | 4-Channel, 104 MSPS Digital Transmit Signal Processor TSP |
| AD6624AS | Four-Channel, 80 MSPS Digital Receive Signal Processor (RSP) |
相关代理商/技术参数 |
参数描述 |
|---|---|
| AD6622AS | 制造商:Analog Devices 功能描述:Transmit Signal Processor 128-Pin MQFP 制造商:Rochester Electronics LLC 功能描述:4 CHANNEL 65 MSPS DIGITAL UPCONVERTER - Bulk |
| AD6622PCB | 制造商:AD 制造商全称:Analog Devices 功能描述:Four-Channel, 75 MSPS Digital Transmit Signal Processor TSP |
| AD6622S | 制造商:AD 制造商全称:Analog Devices 功能描述:Four-Channel, 75 MSPS Digital Transmit Signal Processor TSP |
| AD6622S/PCB | 制造商:AD 制造商全称:Analog Devices 功能描述:Four-Channel, 75 MSPS Digital Transmit Signal Processor TSP |
| AD6623 | 制造商:Analog Devices 功能描述: |
发布紧急采购，3分钟左右您将得到回复。