參數(shù)資料
型號(hào)： AD9767AST
廠商： ANALOG DEVICES INC
元件分類： DAC
英文描述： 14-Bit, 125 MSPS Dual TxDAC+ D/A Converter
中文描述： DUAL, PARALLEL, WORD INPUT LOADING, 0.035 us SETTLING TIME, 14-BIT DAC, PQFP48
封裝： MS-026BBC, LQFP-48
文件頁(yè)數(shù)： 16/27頁(yè)
文件大?。?/td> 469K
代理商： AD9767AST
REV. B
AD9767
–16–
Proper grounding and decoupling should be a primary objective
in any high speed, high resolution system. The AD9767 features
separate analog and digital supply and ground pins to optimize
the management of analog and digital ground currents in a
system. In general, AVDD, the analog supply, should be de-
coupled to ACOM, the analog common, as close to the chip as
physically possible. Similarly, DVDD, the digital supply, should
be decoupled to DCOM as close to the chip as physically possible.
For those applications that require a single +5 V or +3 V supply
for both the analog and digital supplies, a clean analog supply
may be generated using the circuit shown in Figure 39. The
circuit consists of a differential LC filter with separate power
supply and return lines. Lower noise can be attained by using
low ESR type electrolytic and tantalum capacitors.
100 F
10
–
22 F
0.1 F
TTL/CMOS
LOGIC
CIRCUITS
+5V
POWER SUPPLY
FERRITE
BEADS
AVDD
ACOM
ELECTROLYTIC
TANTALUM
CERAMIC
Figure 39. Differential LC Filter for Single +5 V and +3 V
Applications
APPLICATION
VDSL Applications Using the AD9767
Very High Frequency Digital Subscriber Line (VDSL) technol-
ogy is growing rapidly in applications requiring data transfer
over relatively short distances. By using QAM modulation and
transmitting the data in Discrete Multiple Tones (DMT), high
data rates can be achieved.
As with other multitone applications, each VDSL tone is ca-
pable of transmitting a given number of bits, depending on the
signal-to-noise ratio (SNR) in a narrow band around that tone.
For a typical VDSL application, the tones are evenly spaced
over the range of several kHz to 10 MHz. At the high frequency
end of this range, performance is generally limited by cable
characteristics and environmental factors, such as external inter-
ferers. Performance at the lower frequencies is much more de-
pendent on the performance of the components in the signal
chain. In addition to in-band noise, intermodulation from other
tones can also potentially interfere with the data recovery for a
given tone. The two graphs in Figure 40 represent a 500 tone
missing bin test vector, with frequencies evenly spaced from
400 Hz to 10 MHz. This test is very commonly done to deter-
mine if distortion will limit the number of bits which can be
transmitted in a tone. The test vector has a series of missing
tones around 750 kHz, which is represented in Figure 40a, and
a series of missing tones around 5 MHz, which is represented in
Figure 40b. In both cases, the spurious free dynamic range
(SFDR) between the transmitted tones and the empty bins is
greater than 60 dB.
FREQUENCY
–
MHz
d
0.665
–
90
–
80
–
70
–
60
–
50
–
40
–
30
–
20
–
100
–
120
–
110
0.685 0.705 0.725 0.745 0.765 0.785 0.805
0.825
Figure 40a. Notch in Missing Bin at 750 kHz Is Down
>60 dB (Peak Amplitude = 0 dBm)
FREQUENCY
–
MHz
4.85
4.90
4.95
5.00
5.05
5.10
5.15
d
–
80
–
60
–
40
–
20
–
100
–
120
Figure 40b. Notch in Missing Bin at 5 MHz Is Down
>60 dB (Peak Amplitude = 0 dBm)
CDMA
Carrier Division Multiple Access, or CDMA, is an air transmit/
receive scheme where the signal in the transmit path is modu-
lated with a pseudorandom digital code (sometimes referred to
as the spreading code). The effect of this is to spread the trans-
mitted signal across a wide spectrum. Similar to a DMT wave-
form, a CDMA waveform containing multiple subscribers can
be characterized as having a high peak to average ratio (i.e.,
crest factor), thus demanding highly linear components in the
transmit signal path. The bandwidth of the spectrum is defined
by the CDMA standard being used, and in operation is imple-
mented by using a spreading code with particular characteristics.
Distortion in the transmit path can lead to power being trans-
mitted out of the defined band. The ratio of power transmitted
in-band to out-of-band is often referred to as Adjacent Channel
Power (ACP). This is a regulatory issue due to the possibility of
interference with other signals being transmitted by air. Regula-
tory bodies define a spectral mask outside of the transmit band,
and the ACP must fall under this mask. If distortion in the
transmit path causes the ACP to be above the spectral mask,
then filtering, or different component selection, is needed to
meet the mask requirements.
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參數(shù)描述
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AD9767ASTZKL1 制造商:Rochester Electronics LLC 功能描述: 制造商:Analog Devices 功能描述:
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