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參數(shù)資料
| 型號： | AD9774ASZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 10/24頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC DAC 14BIT 32MSPS 44-MQFP |
| 產(chǎn)品培訓模塊： | DAC Architectures |
| 產(chǎn)品變化通告： | Product Discontinuance 27/Oct/2011 |
| 標準包裝： | 1 |
| 系列： | TxDAC+® |
| 設置時間： | 35ns |
| 位數(shù)： | 14 |
| 數(shù)據(jù)接口： | 并聯(lián) |
| 轉(zhuǎn)換器數(shù)目： | 1 |
| 電壓電源： | 模擬和數(shù)字 |
| 功率耗散（最大）： | 1.13W |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 44-QFP |
| 供應商設備封裝： | 44-MQFP（10x10） |
| 包裝： | 托盤 |
| 輸出數(shù)目和類型： | 2 電流，單極；2 電流，雙極 |
| 采樣率（每秒）： | 32M |
AD9774
–18–
REV. B
MULTITONE PERFORMANCE CONSIDERATIONS AND
CHARACTERIZATION
The frequency domain performance of high speed DACs has
traditionally been characterized by analyzing the spectral output
of a reconstructed full-scale (i.e., 0 dBFS), single-tone sine wave
at a particular output frequency and update rate. Although this
characterization data is useful, it is often insufficient to reflect a
DAC’s performance for a reconstructed multitone or spread-
spectrum waveform. In fact, evaluating a DAC’s spectral
performance using a full-scale, single tone at the highest specified
frequency (i.e., fH) of a bandlimited waveform is typically
indicative of a DAC’s “worst-case” performance for that given
waveform. In the time domain, this full-scale sine wave repre-
sents the lowest peak-to-rms ratio or crest factor (i.e., VPEAK/
V rms) that this bandlimited signal will encounter.
10dB
–
DIV
–100
–60
–90
0
16
48
12
0
–50
–70
–80
–30
–40
–10
–20
14
26
10
Figure 42a. Multitone Spectral Plot
TIME
1.0000
0.8000
–1.0000
VOLTS
–0.2000
–0.4000
–0.6000
–0.8000
0.2000
0.0000
0.4000
0.6000
Figure 42b. Time Domain “Snapshot” of the Multitone
Waveform
However, the inherent nature of a multitone, spread spectrum,
or QAM waveform, in which the spectral energy of the wave-
form is spread over a designated bandwidth, will result in a
higher peak-to-rms ratio when compared to the case of a simple
sine wave. As the reconstructed waveform’s peak-to-average
ratio increases, an increasing amount of the signal energy is
concentrated around the DAC’s midscale value. Figure 42a is
just one example of a bandlimited multitone vector (i.e., eight
tones) centered around one-half the Nyquist bandwidth (i.e.,
fCLOCK/4). This particular multitone vector, has a peak-to-rms
ratio of 13.5 dB compared to a sine waves peak-to-rms ratio of
3 dB. A “snapshot” of this reconstructed multitone vector in the
time domain as shown in Figure 43b reveals the higher signal
content around the midscale value. As a result, a DAC’s “small-
scale” dynamic and static linearity becomes increasingly critical in
obtaining low intermodulation distortion and maintaining
sufficient carrier-to-noise ratios for a given modulation scheme.
A DAC’s small-scale linearity performance is also an important
consideration in applications where additive dynamic range is
required for gain control purposes or “predistortion” signal
conditioning. For instance, a DAC with sufficient dynamic
range can be used to provide additional gain control of its
reconstructed signal. In fact, the gain can be controlled in
6 dB increments by simply performing a shift left or right on the
DAC’s digital input word. Other applications may intentionally
predistort a DAC’s digital input signal to compensate for
nonlinearities associated with the subsequent analog compo-
nents in the signal chain. For example, the signal compression
associated with a power amplifier can be compensated for by
predistorting the DAC’s digital input with the inverse nonlinear
transfer function of the power amplifier. In either case, the
DAC’s performance at reduced signal levels should be carefully
evaluated.
A full-scale single tone will induce all of the dynamic and static
nonlinearities present in a DAC that contribute to its distortion
and hence SFDR performance. As the frequency of this recon-
structed full-scale, single-tone waveform increases, the dynamic
nonlinearities of any DAC (i.e., AD9774) tend to dominate thus
contributing to the roll-off in its SFDR performance. However,
unlike most DACs, which employ an R-2R ladder for the lower
bit current segmentation, the AD9774 (as well as other TxDAC
members) exhibits an improvement in distortion performance as
the amplitude of a single tone is reduced from its full-scale level.
This improvement in distortion performance at reduced signal
levels is evident if one compares the SFDR performance vs.
frequency at different amplitudes (i.e., 0 dBFS, –6 dBFS and
–12 dBFS) and sample rates as shown in Figures 4 through 15.
Maintaining decent “small-scale” linearity across the full span of
a DAC transfer function is also critical in maintaining excellent
multitone performance.
Although characterizing a DAC’s multitone performance tends
to be application-specific, much insight into the potential per-
formance of a DAC can also be gained by evaluating the DAC’s
swept power (i.e., amplitude) performance for single, dual and
multitone test vectors at different clock rates and carrier frequen-
cies. The DAC is evaluated at different clock rates when recon-
structing a specific waveform whose amplitude is decreased in
3 dB increments from full-scale (i.e., 0 dBFS). For each specific
waveform, a graph showing the SFDR (over Nyquist) perfor-
mance vs. amplitude can be generated at the different tested
clock rates as shown in Figures 19 and 20. Note that the
carrier(s)-to-clock ratio remains constant in each figure.
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| AD9774ASZRL | 功能描述:IC DAC 14BIT 32MSPS 44MQFP RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 數(shù)模轉(zhuǎn)換器 系列:TxDAC+® 標準包裝:2,400 系列:- 設置時間:- 位數(shù):18 數(shù)據(jù)接口:串行 轉(zhuǎn)換器數(shù)目:3 電壓電源:模擬和數(shù)字 功率耗散（最大）:- 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:36-TFBGA 供應商設備封裝:36-TFBGA 包裝:帶卷 (TR) 輸出數(shù)目和類型:* 采樣率（每秒）:* |
| AD9774EB | 制造商:AD 制造商全稱:Analog Devices 功能描述:14-Bit, 32 MSPS TxDAC⑩ with 4x Interpolation Filters |
| AD9774-EB | 制造商:Analog Devices 功能描述: |
| AD9774-EBZ | 制造商:Analog Devices 功能描述:14-BIT 32 MSPS TXDAC W/4X INTERPOLATION - Bulk |
| AD9775 | 制造商:AD 制造商全稱:Analog Devices 功能描述:14-Bit, 160 MSPS 2X/4X/8X Interpolating Dual TxDAC+ D/A Converter |
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