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參數資料
| 型號： | AD9873 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Analog Front End Converter for Set-Top Box, Cable Modem |
| 中文描述： | 模擬前端轉換器，用于機頂盒，電纜調制解調器 |
| 文件頁數： | 27/39頁 |
| 文件大小： | 935K |
| 代理商： | AD9873 |
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REV. 0
AD9873
–27–
FREQUENCY RELATIVE TO I/Q NYQ. BW
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Figure 10d. Cascaded Filter Passband Detail (N = 3)
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Figure 12b. SINC Compensated Response
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ISF
SINC
Figure 12a. SINC and ISF Filter Response
FREQUENCY RELATIVE TO I/Q NYQ. BW
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Figure 11d. Cascaded Filter Passband Detail (N = 4)
Inverse SINC Filter (ISF)
The AD9873 transmit section is almost entirely digital. The input
“
signal
”
is made up of a time series of digital data words. These
data words propagate through the device as numbers. Ultimately,
this number stream must be converted to an analog signal. To this
end, the AD9873 incorporates an integrated DAC. The output
waveform of the DAC is the familiar
“
staircase
”
pattern typical
of a signal that is sampled and quantized. The staircase pattern
is a result of the finite time that the DAC holds a quantized level
until the next sampling instant. This is known as a zero-order hold
function. The spectrum of the zero-order hold function is the
familiar SIN(x)/x, or SINC, envelope.
The series of digital data words presented at the input of the DAC
represent an impulse stream. It is the spectrum of this impulse
stream, which is the characteristic of the desired output signal.
Due to the zero-order hold effect of the DAC, however, the output
spectrum is the product of the zero-order hold spectrum (the
SINC envelope) and the Fourier transform of the impulse stream.
Thus, there is an intrinsic distortion in the output spectrum,
which follows the SINC response.
The SINC response is deterministic and totally predictable. Thus,
it is possible to predistort the input data stream in a manner,
which compensates for the SINC envelope distortion. This can
be accomplished by means of an ISF. The ISF incorporated on
the AD9873 is a 5-tap, linear phase FIR filter. Its frequency
response characteristic is the inverse of the SINC envelope and
it equalizes the SINC droop up to 0.6 times the Nyquist fre-
quency. Figure 12a and Figure 12b show the effectiveness of the
ISF in correcting for the SINC distortion. Figure 12a includes a
graph of the SINC envelope and ISF response while Figure 12b
shows the SYSTEM response (which is the product of the SINC
and ISF responses). It should be mentioned at this point that
the ISF exhibits an insertion loss of 1.4 dB. Thus, signal levels
at the output of the AD9873 with the ISF bypassed are 1.4 dB
higher than with the ISF engaged. However, for modulated
output signals, which have a relatively wide bandwidth, the ben-
efits of the SINC compensation usually outweighed the 1.4dB
loss in output level. The decision of whether or not to use the
ISF is an application specific system design issue.
相關PDF資料 |
PDF描述 |
|---|---|
| AD9873-EB | Analog Front End Converter for Set-Top Box, Cable Modem |
| AD9873JS | Analog Front End Converter for Set-Top Box, Cable Modem |
| AD9874 | IF Digitizing Subsystem |
| AD9874BST | IF Digitizing Subsystem |
| AD9874EB | IF Digitizing Subsystem |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD9873-EB | 制造商:Analog Devices 功能描述: |
| AD9873JS | 制造商:Analog Devices 功能描述: |
| AD9874 | 制造商:AD 制造商全稱:Analog Devices 功能描述:IF Digitizing Subsystem |
| AD9874ABST | 功能描述:IC IF DIGIT SUBSYSTEM 48-LQFP RoHS:否 類別:RF/IF 和 RFID >> RF 其它 IC 和模塊 系列:- 標準包裝:100 系列:* |
| AD9874ABST | 制造商:Analog Devices 功能描述:IF DIGITIZING SYBSYSTEM ((NW)) 制造商:Analog Devices 功能描述:IC, IF DIGITIZING SUBSYSTEM, LQFP-48 |
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