参数资料
型号: AD9649BCPZ-20
厂商: Analog Devices Inc
文件页数: 10/32页
文件大小: 0K
描述: IC ADC 14BIT 20MSPS 32LFCSP
标准包装: 1
位数: 14
采样率(每秒): 20M
数据接口: 串行,SPI?
转换器数目: 1
功率耗散(最大): 51.8mW
电压电源: 模拟和数字
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 32-VFQFN 裸露焊盘,CSP
供应商设备封装: 32-LFCSP-VQ
包装: 托盘
输入数目和类型: 2 个单端,单极;1 个差分,单极
AD9649
Rev. 0 | Page 18 of
32
Differential Input Configurations
Optimum performance is achieved while driving the AD9649
in a differential input configuration. For baseband applications,
the AD8138, ADA4937-2, and ADA4938-2 differential drivers
provide excellent performance and a flexible interface to the ADC.
The output common-mode voltage of the ADA4938-2 is easily
set with the VCM pin of the AD9649 (see Figure 38), and the
driver can be configured in a Sallen-Key filter topology to
provide band limiting of the input signal.
AVDD
VIN
76.8
120
0.1F
33
33
10pF
200
200
90
ADA4938-2
ADC
VIN–
VIN+
VCM
08
53
9-
00
7
Figure 38. Differential Input Configuration Using the ADA4938-2
For baseband applications below ~10 MHz where SNR is a key
parameter, differential transformer coupling is the recommended
input configuration. An example is shown in Figure 39. To bias
the analog input, the VCM voltage can be connected to the
center tap of the secondary winding of the transformer.
2V p-p
49.9
0.1F
R
C
ADC
VCM
VIN+
VIN–
08
53
9-
0
08
Figure 39. Differential Transformer-Coupled Configuration
The signal characteristics must be considered when selecting
a transformer. Most RF transformers saturate at frequencies
below a few megahertz (MHz). Excessive signal power can also
cause core saturation, which leads to distortion.
At input frequencies in the second Nyquist zone and above, the
noise performance of most amplifiers is not adequate to achieve
the true SNR performance of the AD9649. For applications above
~10 MHz where SNR is a key parameter, differential double balun
coupling is the recommended input configuration (see Figure 41).
An alternative to using a transformer-coupled input at frequencies
in the second Nyquist zone is to use the AD8352 differential driver.
An example is shown in Figure 42. See the AD8352 data sheet
for more information.
In any configuration, the value of Shunt Capacitor C is dependent
on the input frequency and source impedance and may need to
be reduced or removed. Table 9 displays the suggested values to set
the RC network. However, these values are dependent on the
input signal and should be used only as a starting guide.
Table 9. Example RC Network
Frequency Range (MHz)
R Series
(Ω Each)
C Differential (pF)
0 to 70
33
22
70 to 200
125
Open
Single-Ended Input Configuration
A single-ended input can provide adequate performance in cost-
sensitive applications. In this configuration, SFDR and distortion
performance degrade due to the large input common-mode swing.
If the source impedances on each input are matched, there should
be little effect on SNR performance. Figure 40 shows a typical
single-ended input configuration.
1V p-p
R
C
49.9
0.1F
10F
0.1F
AVDD
1k
1k
1k
1k
ADC
AVDD
VIN+
VIN–
08
53
9-
00
9
Figure 40. Single-Ended Input Configuration
ADC
R
0.1F
2V p-p
VCM
C
R
0.1F
S
0.1F
25
25
S
PA
P
VIN+
VIN–
08
53
9-
01
0
Figure 41. Differential Double Balun Input Configuration
AD8352
0
0
CD
RD
RG
0.1F
16
1
2
3
4
5
11
0.1F
10
14
0.1F
8, 13
VCC
200
200
ANALOG INPUT
R
C
ADC
VCM
VIN+
VIN–
08
53
9-
01
1
Figure 42. Differential Input Configuration Using the AD8352
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