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參數資料
| 型號： | AD9877-EB |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Mixed-Signal Front End Set-Top Box, Cable Modem |
| 中文描述： | 混合信號前端機頂盒，電纜調制解調器 |
| 文件頁數： | 24/36頁 |
| 文件大小： | 1094K |
| 代理商： | AD9877-EB |
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AD9877
TRANSMIT PATH (Tx)
Rev. B | Page 24 of 36
t
SU
t
HD
MCLK
TxSYNC
TxIQ
TxI[11:6]
TxI[5:0]
TxQ[11:6]
TxQ[5:0]
TxI[11:6]
TxI[5:0]
TxQ[11:6]
TxQ[5:0]
TxI[11:6]
TxI[5:0]
0
Figure 26. Transmit Timing Diagram
TRANSMIT TIMING
The AD9877 provides a master clock, MCLK, and expects 6-bit
multiplexed TxIQ data upon each rising edge. Transmit
symbols are framed with the TxSYNC input. TxSYNC high
indicates the start of a transmit symbol. Four consecutive 6-bit
data packages form a symbol (I MSB, I LSB, Q MSB, and Q LSB).
DATA ASSEMBLER
The input data stream is representative complex data. Two 6-bit
words form a 12-bit symbol component (twos complement
format). Four input samples are required to produce one I/Q
data pair. The I/Q sample rate, f
IQCLK
, at the input to the first
half-band filter is a quarter of the input data rate, f
MCLK
.
The I/Q sample rate, f
IQCLK
, puts a bandwidth limit on the
maximum transmit spectrum. This is the familiar Nyquist limit
and is equal to one-half f
IQCLK
, hereafter referred to as f
NYQ
.
HALF-BAND FILTERS (HBFs)
HBF 1 and HBF 2 are both interpolating filters, each of which
doubles the sampling rate. Together, HBF 1 and HBF 2 have
26 taps and provide a factor of 4 increase in the sampling rate
(4 × f
IQCLK
or 8 × f
NYQ
).
In relation to phase response, both HBFs are linear phase filters.
As such, virtually no phase distortion is introduced within the
pass band of the filters. This is an important feature, because
phase distortion is generally intolerable in a data transmission
system.
CASCADED INTEGRATOR-COMB (CIC) FILTER
A CIC filter is unlike a typical FIR filter in that it offers the
flexibility to handle differing input and output sample rates in
any integer ratios. In the AD9877, the CIC filter is configured as
a programmable interpolator and provides a sample rate
increase by a factor of R = 3 or R = 4. In addition to the ability
to provide a change in the sample rate between the input and
output, a CIC filter has an intrinsic low-pass frequency response
characteristic.
The frequency response of a CIC filter is dependent on three
factors:
The rate change ratio,
R
.
The order of the filter,
n
.
The number of unit delays per stage,
m
.
It can be shown that the system function
H(z)
of a CIC filter is
given by
n
Rm
∑
k
k
Rm
z
R
z
z
R
Hz
=
1
=
=
1
0
1
1
1
1
The form on the far right has the advantage of providing a
result for
z
= 1 (corresponding to zero frequency or dc). The
alternate form yields an indeterminate form (0/0) for
z
= 1, but
is otherwise identical. The only variable parameter for the CIC
filter of the AD9877 is
R
;
m
and
n
are fixed at 1 and 3,
respectively. Thus, the CIC system function for the AD9877
simplifies to
3
1
0
3
1
1
R
1
1
1
R
=
=
∑
=
k
Rm
k
R
z
z
z
Hz
The transfer function is given by
( )
(
)
(
( )
π
)
3
3
)
2
j
/
2
sin
sin
1
R
1
1
1
R
π
=
=
π
π
fR
e
e
H
f
R
j
The frequency response in this form is such that
f
is scaled to
the output sample rate of the CIC filter. That is,
f
= 1
corresponds to the frequency of the output sample rate of the
CIC filter.
H(z)
yields the frequency response with respect to
the input sample of the CIC filter.
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相關代理商/技術參數 |
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| AD9878 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Mixed-Signal Front End for Broadband Applications |
| AD9878BST | 制造商:Analog Devices 功能描述:Mixed Signal Front End 100-Pin LQFP |
| AD9878BSTRL | 制造商:Analog Devices 功能描述:Mixed Signal Front End 100-Pin LQFP T/R 制造商:Analog Devices 功能描述:MIXED SGNL FRONT END 100LQFP - Tape and Reel |
| AD9878BSTZ | 功能描述:IC FRONT-END MIXED-SGNL 100-LQFP RoHS:是 類別:集成電路 (IC) >> 數據采集 - 模擬前端 (AFE) 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:- 位數:- 通道數:2 功率（瓦特）:- 電壓 - 電源，模擬:3 V ~ 3.6 V 電壓 - 電源，數字:3 V ~ 3.6 V 封裝/外殼:32-VFQFN 裸露焊盤 供應商設備封裝:32-QFN（5x5） 包裝:帶卷 (TR) |
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