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| 型号： | AD9220ARS |
| 厂商： | ANALOG DEVICES INC |
| 元件分类： | ADC |
| 英文描述： | Complete 12-Bit 1.5/3.0/10.0 MSPS Monolithic A/D Converters |
| 中文描述： | 1-CH 12-BIT FLASH METHOD ADC, PARALLEL ACCESS, PDSO28 |
| 封装： | MO-150AH, SSOP-28 |
| 文件页数： | 17/28页 |
| 文件大小： | 350K |
| 代理商： | AD9220ARS |
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AD9221/AD9223/AD9220
REV. D
–17–
DIFFERENTIAL MODE OF OPERATION
Since not all applications have a signal preconditioned for differ-
ential operation, there is often a need to perform a single-ended-
to-differential conversion. In systems which do not need to be
dc coupled, an RF transformer with a center tap is the best
method to generate differential inputs for the AD9221/AD9223/
AD9220. It provides all the benefits of operating the A/D in the
differential mode without contributing additional noise or dis-
tortion. An RF transformer also has the added benefit of provid-
ing electrical isolation between the signal source and the A/D.
Note that although a single-ended-to-differential op amp topol-
ogy would allow dc coupling of the input signal, no significant
improvement in THD performance was realized when compared
to the dc single-ended mode of operation up to the AD9221/
AD9223/AD9220’s Nyquist frequency (i.e., f
IN
< F
S
/2). Also,
the additional op amp required in the topology tends to in-
creases the total system noise, power consumption, and cost.
Hence, a single-ended mode of operation is recommended for
most applications requiring dc coupling.
A dramatic improvement in THD and SFDR performance can
be realized by operating the AD9221/AD9223/AD9220 in the
differential mode using a transformer. Figure 43 shows a plot of
THD vs. Input Frequency for the differential transformer
coupled circuit for each A/D while Figure 44 shows a plot of
SFDR vs. Input Frequency. Both figures demonstrate the enhance-
ment in spectral performance for the differential-mode of opera-
tion. The performance enhancement between the differential
and single-ended mode is most noteworthy as the input frequency
approaches and goes beyond the Nyquist frequency (i.e., f
IN
>
F
S
/2) corresponding to the particular A/D.
The figures are also helpful in determining the appropriate A/D
for Direct IF-Down Conversion or undersampling applications.
Refer to Analog Devices application notes AN-301 and AN-302
for an informative discussion on undersampling. One should
select the A/D that meets or exceeds the distortion performance
requirements measured over the required frequency passband.
For example, the AD9220 achieves the best distortion perfor-
mance over an extended frequency range as a result of its greater
full-power bandwidth and thus would represent the best selec-
tion for an IF undersampling application at 21.4 MHz. Refer to
the Applications section of this data sheet for more detailed
information and characterization of this particular application.
T
FREQUENCY – MHz
–50
–60
–90
1
100
10
–70
–80
AD9221
AD9223
AD9220
Figure 43. AD9221/AD9223/AD9220 THD vs. Input Fre-
quency (V
CM
= 2.5 V, 2 V p-p Input Span, A
IN
= –0.5 dB)
FREQUENCY – MHz
–55
–95
1
100
10
S
–65
–75
–85
AD9221
AD9223
AD9220
Figure 44. AD9221/AD9223/AD9220 SFDR vs. Input Fre-
quency (V
CM
= 2.5 V, 2 V p-p Input Span, A
IN
= –0.5 dB)
Figure 45 shows the schematic of the suggested transformer
circuit. The circuit uses a minicircuits RF transformer, model
#T4-6T, which has an impedance ratio of four (turns ratio of
2). The schematic assumes that the signal source has a 50
source impedance. The 1:4 impedance ratio requires the 200
secondary termination for optimum power transfer and VSWR.
The center tap of the transformer provides a convenient means
of level shifting the input signal to a desired common-mode
voltage. Optimum performance can be realized when the center
tap is tied to CML of the AD9221/AD9223/AD9220 which is
the common-mode bias level of the internal SHA.
VINA
VINB
AD9221/
AD9223/
AD9220
200
V
49.9
V
R
S
33
V
CML
C
S
15pF
MINI CIRCUITS
T4-1
0.1
m
F
R
S
33
V
C
S
15pF
Figure 45. Transformer Coupled Input
Transformers with other turns ratios may also be selected to
optimize the performance of a given application. For example,
a given input signal source or amplifier may realize an improve-
ment in distortion performance at reduced output power levels
and signal swings. Hence, selecting a transformer with a higher
impedance ratio (e.g., Minicircuits T16-6T with a 1:16 imped-
ance ratio) effectively “steps up” the signal level thus further
reducing the driving requirements of the signal source.
Referring to Figure 45, a series resistors, R
S
, and shunt capaci-
tor, C
S
, were inserted between the AD9221/AD9223/AD9220
and the secondary of the transformer. The values of 33
and
15 pF were selected to specifically optimize both the THD and
SNR performance of the A/D. R
S
and C
S
help provide some
isolation from transients at the A/D inputs reflected back
through the primary of the transformer.
The AD9221/AD9223/AD9220 can be easily configured for
either a 2 V p-p input span or 5.0 V p-p input span by setting
the internal reference (see Table II). Other input spans can be
realized with two external gain setting resistors as shown in
Figure 49 of this data sheet. Figure 46 demonstrates how both
spans of the AD9220 achieve the high degree of linearity and
相关PDF资料 |
PDF描述 |
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| AD9221 | Complete 12-Bit 1.5/3.0/10.0 MSPS Monolithic A/D Converters |
| AD9221AR | RES, 18.2K, 1/4, 1%, MF |
| AD9221ARS | Complete 12-Bit 1.5/3.0/10.0 MSPS Monolithic A/D Converters |
| AD9223 | Complete 12-Bit 1.5/3.0/10.0 MSPS Monolithic A/D Converters |
| AD9223AR | Complete 12-Bit 1.5/3.0/10.0 MSPS Monolithic A/D Converters |
相关代理商/技术参数 |
参数描述 |
|---|---|
| AD9220ARS-REEL | 功能描述:IC ADC 12BIT 10MSPS 28-SSOP RoHS:否 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 标准包装:1,000 系列:- 位数:16 采样率（每秒）:45k 数据接口:串行 转换器数目:2 功率耗散（最大）:315mW 电压电源:模拟和数字 工作温度:0°C ~ 70°C 安装类型:表面贴装 封装/外壳:28-SOIC（0.295"，7.50mm 宽） 供应商设备封装:28-SOIC W 包装:带卷 (TR) 输入数目和类型:2 个单端，单极 |
| AD9220ARSZ | 功能描述:IC ADC 12BIT 10MSPS 28-SSOP RoHS:是 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 标准包装:1 系列:microPOWER™ 位数:8 采样率（每秒）:1M 数据接口:串行，SPI? 转换器数目:1 功率耗散（最大）:- 电压电源:模拟和数字 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:24-VFQFN 裸露焊盘 供应商设备封装:24-VQFN 裸露焊盘（4x4） 包装:Digi-Reel® 输入数目和类型:8 个单端，单极 产品目录页面:892 (CN2011-ZH PDF) 其它名称:296-25851-6 |
| AD9220ARSZ | 制造商:Analog Devices 功能描述:IC ADC 12BIT 10MSPS ((NW)) 制造商:Analog Devices 功能描述:IC, ADC, 12BIT, 10MSPS, SSOP-28 |
| AD9220ARSZ-REEL | 功能描述:IC ADC 12BIT 10MSPS 28-SSOP RoHS:是 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 标准包装:1,000 系列:- 位数:16 采样率（每秒）:45k 数据接口:串行 转换器数目:2 功率耗散（最大）:315mW 电压电源:模拟和数字 工作温度:0°C ~ 70°C 安装类型:表面贴装 封装/外壳:28-SOIC（0.295"，7.50mm 宽） 供应商设备封装:28-SOIC W 包装:带卷 (TR) 输入数目和类型:2 个单端，单极 |
| AD9220ARZ | 功能描述:IC ADC 12BIT 10MSPS 28-SOIC RoHS:是 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 标准包装:1,000 系列:- 位数:12 采样率（每秒）:300k 数据接口:并联 转换器数目:1 功率耗散（最大）:75mW 电压电源:单电源 工作温度:0°C ~ 70°C 安装类型:表面贴装 封装/外壳:24-SOIC（0.295"，7.50mm 宽） 供应商设备封装:24-SOIC 包装:带卷 (TR) 输入数目和类型:1 个单端，单极；1 个单端，双极 |
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