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參數(shù)資料
| 型號(hào)： | AD9874 |
| 廠(chǎng)商： | ANALOG DEVICES INC |
| 元件分類(lèi)： | 通信及網(wǎng)絡(luò) |
| 英文描述： | IF Digitizing Subsystem |
| 中文描述： | SPECIALTY TELECOM CIRCUIT, PQFP48 |
| 封裝： | 1.40 MM HEIGHT, PLASTIC, TQFP-48 |
| 文件頁(yè)數(shù)： | 25/40頁(yè) |
| 文件大小： | 744K |
| 代理商： | AD9874 |
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REV. 0
AD9874
–25–
Once the AD9874 has been tuned, the noise figure degradation
attributed solely to the temperature drift of the LC and RC resona-
tors is minimal. Since the drift of the RC resonator is actually
negligible compared to that of the LC resonator, the external
L and C components’ temperature drift characteristics tend to
dominate. Figure 13d shows the degradation in noise figure as the
product of the LC value is allowed to vary from –12.5% to +12.5%.
Note, the noise figure remains relatively constant over a
±
3.5%
range (i.e.,
±
35,000 ppm) suggesting that most applications will
not be required to retune over the operating temperature range.
–15
12
11
N
10
LC ERROR – %
9
8
0
5
10
15
–5
–10
BW = 75kHz
BW = 10kHz
BW = 30kHz
Figure 13d. Typical Noise Figure Degradation from L and
C Component Drift (f
CLK
= 18 MSPS, f
IF
= 73.3501 MHz)
DECIMATION FILTER
The decimation filter shown in Figure 14 consists of an
f
CLK
/8
complex mixer and a cascade of three linear phase FIR filters:
DEC1, DEC2, and DEC3. DEC1 downsamples by a factor of 12
using a fourth order comb filter. DEC2 also uses a fourth order
comb filter, but its decimation factor is set by the M field of
Register 0x07. DEC3 is either a decimate-by-5 FIR filter or a
decimate-by-4 FIR filter depending on the value of the K Bit within
Register 0x07. Thus, the composite decimation factor can be set
to either 60
×
M or 48
×
M for K equal to 0 or 1, respectively.
The output data rate (f
OUT
) is equal to the modulator clock
frequency (f
CLK
) divided by the digital filter’s decimation factor.
Due to the transition region associated with the decimation
filter’s frequency response, the decimation factor must be
selected such that f
OUT
is equal to or greater than twice the signal
bandwidth. This ensures low amplitude ripple in the pass band
along with the ability to provide further application-specific
digital filtering prior to demodulation.
4
OR
5
COS
SIN
DATA
FROM -
MODULATOR
DEC1
SINC
4
FILTER
12
DEC2
SINC
4
FILTER
M
+
1
M
DEC3
FIR
FILTER
K
I
Q
COMPLEX
DATA TO
Figure 14. Decimation Filter Architecture
Figure 15a shows the response of the decimation filter at a decimation
factor of 900 (K = 0, M = 14) and a sampling clock frequency of
18 MHz. In this example, the output data rate (
f
OUT
) is 20 kSPS,
with a usable complex signal bandwidth of 10 kHz centered around
dc. As this figure shows, the first and second alias bands (occurring
at even integer multiples of
f
OUT
/2) have the least attenuation but
provide at least 88 dB of attenuation. Note, signals falling around
frequency offsets that are odd integer multiples of
f
OUT
/2 (i.e.,
10 kHz, 30 kHz, and 50 kHz) will fall back into the transition
band of the digital filter.
FREQUENCY – kHz
0
–40
–100
0
30
10
20
–20
–60
–80
40
100
d
FOLD-
ING
POINT
5.0kHz PASS BAND
–120
70
80
60
50
90
–88dB
–88dB
–101dB
–103dB
Figure 15a. Decimation Filter Frequency Response
for f
OUT
= 20 kSPS (f
CLK
= 18 MHz, OSR = 900)
Figure 15b shows the response of the decimation filter with a
decimation factor of 48 and a sampling clock rate of 26 MHz. The
alias attenuation is now at least 94 dB, and this attenuation occurs
for frequencies at the edges of the fourth alias band. The differ-
ence between the alias attenuation characteristics of Figure 15b
and those of Figure 15a is due to the fact that the third decimation
stage decimates by a factor of 5 for Figure 15a versus a factor of 4
for Figure 15b.
0
–40
–100
–20
–60
–80
d
–120
FREQUENCY – MHz
0
1.5
0.5
1.0
2.0
2.5
135.466kHz PASS BAND
–98dB
–115dB
–94dB
Figure 15b. Decimation Filter Frequency Response
for f
OUT
= 541.666 kSPS (f
CLK
= 26 MHz, OSR = 48)
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AD9874BST | IF Digitizing Subsystem |
| AD9874EB | IF Digitizing Subsystem |
| AD9875BSTRL | Broadband Modem Mixed-Signal Front End |
| AD9875 | Broadband Modem Mixed-Signal Front End |
| AD9875-EB | Broadband Modem Mixed-Signal Front End |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD9874ABST | 功能描述:IC IF DIGIT SUBSYSTEM 48-LQFP RoHS:否 類(lèi)別:RF/IF 和 RFID >> RF 其它 IC 和模塊 系列:- 標(biāo)準(zhǔn)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 |
| AD9874ABST | 制造商:Analog Devices 功能描述:IC IF DIG SUBSYSTEM |
| AD9874ABSTRL | 功能描述:IC IF DIGIT SUBSYSTEM 48-LQFP RoHS:否 類(lèi)別:RF/IF 和 RFID >> RF 其它 IC 和模塊 系列:- 標(biāo)準(zhǔn)包裝:100 系列:* |
| AD9874ABSTZ | 制造商:AD 制造商全稱(chēng):Analog Devices 功能描述:IF Digitizing Subsystem |
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