參數(shù)資料
型號: AD8138ARZ
廠商: ANALOG DEVICES INC
元件分類: 通用總線功能
英文描述: Low Distortion Differential ADC Driver
中文描述: LINE DRIVER, PDSO8
封裝: LEAD FREE, MS-012AA, SOIC-8
文件頁數(shù): 22/24頁
文件大?。?/td> 318K
代理商: AD8138ARZ
AD8138
3 V OPERATION
The circuit in Figure 47 shows a simplified front-end
connection for an AD8138 driving an
AD9203
, a 10-bit,
40 MSPS ADC that is specified to work on a single 3 V supply.
The ADC works best when driven differentially to make the
best use of the signal swing available within the 3 V supply.
The appropriate outputs of the AD8138 are connected to the
appropriate differential inputs of the
AD9203
via a low-pass filter.
Rev. F | Page 22 of 24
The AD8138 is configured for unity gain for a single-ended
input to differential output. The additional 23 Ω at the input to
IN is to balance the impedance of the 50 Ω source and its 50 Ω
termination that drives the noninverting input.
The signal generator has ground-referenced, bipolar output,
that is, it can drive symmetrically above and below ground.
Even though the AD8138 has ground as its negative supply, it
can still function as a level-shifter with such an input signal.
The output common mode is raised up to midsupply by the
voltage divider that biases V
OCM
. In this way, the AD8138
provides dc coupling and level-shifting of a bipolar signal,
without inverting the input signal.
The low-pass filter between the AD8138 and the
AD9203
provides filtering that helps to improve the signal-to-noise ratio
(SNR). Lower noise can be realized by lowering the pole
frequency, but the bandwidth of the circuit is lowered.
49.9
0.1μF
10k
523
499
10k
20pF
49.9
20pF
499
499
0.1μF
3V
DRVDD
AVDD
AINN
AINP
26
0.1μF
0.1μF
3V
49.9
AD8138
+
AD9203
8
2
1
3
5
4
6
28
2
27
25
1
AVSS
DRVSS
DIGITAL
0
Figure 47. AD8138 Driving an
AD9203
, a 10-Bit, 40 MSPS A/D Converter
The circuit was tested with a 0.5 dBFS signal at various
frequencies. Figure 48 shows a plot of the total harmonic
distortion (THD) vs. frequency at signal amplitudes of 1 V and
2 V differential drive levels.
FREQUENCY (MHz)
–40
T
–45
–50
–55
–60
–65
–70
–75
–80
AD8138–2V
AD8138–1V
0
5
10
15
20
25
0
Figure 48.
AD9203
THD @ 0.5 dBFS AD8138
Figure 49 shows the signal-to-noise-plus distortion (SINAD)
under the same conditions as above. For the smaller signal
swing, the AD8138 performance is quite good, but its
performance degrades when trying to swing too close to the
supply rails.
FREQUENCY (MHz)
65
S
63
61
59
57
55
53
51
45
49
47
AD8138–1V
AD8138–2V
0
5
10
15
20
25
0
Figure 49.
AD9203
SINAD @ 0.5 dBFS AD8138
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