参数资料
| 型号： | AD9042ASTZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 8/24页 |
| 文件大小： | 0K |
| 描述： | IC ADC 12BIT 41MSPS 44-TQFP |
| 标准包装： | 1 |
| 位数： | 12 |
| 采样率（每秒）： | 41M |
| 数据接口： | 并联 |
| 转换器数目： | 3 |
| 功率耗散（最大）： | 735mW |
| 电压电源： | 模拟和数字，双 ± |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 44-LQFP |
| 供应商设备封装： | 44-LQFP（10x10） |
| 包装： | 托盘 |
| 输入数目和类型： | 1 个单端，双极 |
| 产品目录页面： | 780 (CN2011-ZH PDF) |
AD9042
Rev. B | Page 16 of 24
DIGITAL WIDEBAND RECEIVERS
INTRODUCTION
Several key technologies are now being introduced that may
forever alter the vision of radio. Figure 36 shows the typical dual
conversion superheterodyne receiver. The signal picked up by
the antenna is mixed down to an intermediate frequency (IF)
using a mixer with a variable local oscillator (LO); the variable
LO is used to tune in the desired signal. This first IF is mixed
down to a second IF using another mixer stage and a fixed LO.
Demodulation takes place at the second or third IF using either
analog or digital techniques.
ADCs
VARIABLE
IF1
IF2
FIXED
NARROW-BAND
FILTER
NARROW-BAND
FILTER
I
Q
LNA
RF
900MHz
SHARED
ONE RECEIVER PER CHANNEL
00
55
4-
05
4
Figure 36. Narrow-Band Digital Receiver Architecture
If demodulation takes place in the analog domain, then traditional
discriminators, envelope detectors, phase-locked loops, or other
synchronous detectors are generally used to strip the modulation
from the selected carrier.
However, as general-purpose DSP chips such as the ADSP-2181
become more popular, they can be used in many baseband
sampled application such as the one shown in Figure 36. As
shown in the figure, prior to ADC conversion, the signal must be
mixed down and filtered, and the I and Q components must be
separated. These functions are realized through DSP techniques;
however, several key technology breakthroughs are required:
high dynamic range ADCs, such as the AD9042, new DSPs
(highly programmable with fast onboard memory), digital
tuner and filter (with programmable frequency and BW), and
wideband mixers (high dynamic range with >12.5 MHz BW).
WIDEBAND
ADC
FIXED
WIDEBAND
MIXER
WIDEBAND
FILTER
LNA
RF
900MHz
SHARED
"n" CHANNELS
TO DSP
12.5MHz
(416 CHANNELS)
CHANNEL SELECTION
0055
4-
0
55
Figure 37. Wideband Digital Receiver Architecture
Figure 37 shows such a wideband system. This design shows
that the front-end variable local oscillator has been replaced
with a fixed oscillator (for single-band radios), and the back end
has been replaced with a wide dynamic range ADC, digital
tuner, and DSP. This technique offers many benefits.
First, many passive discrete components that formed the tuning
and filtering functions have been eliminated. These passive
components often require adjusting and special handling
during assembly and final system alignment. Digital
components require no such adjustments; tuner and filter
characteristics are always exactly the same. Moreover, the
tuning and filtering characteristics can be changed through
software. Because software is used for demodulation, different
routines may be used to demodulate different standards such as
AM, FM, GMSK, or any other desired standard. In addition, as
new standards arise or new software revisions are generated,
they may be field installed with standard software update
channels. A radio that performs demodulation in software as
opposed to hardware is often referred to as a soft radio because
it c
an be changed or modified simply through code revision.
System Description
In the wideband digital radio (see Figure 37), the first down-
conversion functions in much the same way as a block converter
does. An entire band is shifted in frequency to the desired
intermediate frequency. In the case of cellular base station
receivers, 5 MHz to 20 MHz of bandwidth are downconverted
simultaneously to an IF frequency suitable for digitizing with a
wideband ADC. Once digitized, the broadband digital data
stream contains all of the in-band signals. The remainder of the
radio is constructed digitally using special-purpose and general-
purpose programmable DSP to perform filtering, demodulation,
and signal conditioning, not unlike the analog counterparts.
In the narrow-band receiver (see Figure 36), the signal to be
received must be tuned. This is accomplished by using a
variable local oscillator at the first mix-down stage. The first IF
then uses a narrow-band filter to reject out-of-band signals and
condition the selected carrier for signal demodulation.
In the digital wideband receiver (see Figure 37), the variable
local oscillator has been replaced with a fixed oscillator, so
tuning must be accomplished in another manner. Tuning is
performed digitally using a digital downconversion and a filter
chip frequently called a channelizer. The term, channelizer, is
used because the purpose of these chips is to select one channel
out of the many within the broadband of spectrum actually
present in the digital data stream of the ADC.
DECIMATION
FILTER
LOW-PASS
FILTER
DIGITAL
TUNER
COS
SIN
DECIMATION
FILTER
LOW-PASS
FILTER
DATA
I
Q
00
55
4-
05
6
Figure 38. Digital Channelizer
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相关代理商/技术参数 |
参数描述 |
|---|---|
| AD9042BD | 制造商:Analog Devices 功能描述:- Bulk |
| AD9042CHIPS | 制造商:AD 制造商全称:Analog Devices 功能描述:12-Bit, 41 MSPS Monolithic A/D Converter |
| AD9042D | 制造商:AD 制造商全称:Analog Devices 功能描述:12-Bit, 41 MSPS Monolithic A/D Converter |
| AD9042D/PCB | 制造商:AD 制造商全称:Analog Devices 功能描述:12-Bit, 41 MSPS Monolithic A/D Converter |
| AD9042DPCB | 制造商:AD 制造商全称:Analog Devices 功能描述:12-Bit, 41 MSPS Monolithic A/D Converter |
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