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參數(shù)資料
| 型號： | AD7664AST |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | 16-Bit, 570 kSPS CMOS ADC |
| 中文描述： | 1-CH 16-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL/PARALLEL ACCESS, PQFP48 |
| 封裝： | MS-026BBC, LQFP-48 |
| 文件頁數(shù)： | 12/19頁 |
| 文件大?。?/td> | 392K |
| 代理商： | AD7664AST |
REV. 0
AD7664
–12–
This analog input structure allows the sampling of the differen-
tial signal between IN and INGND. Unlike other converters,
the INGND input is sampled at the same time as the IN input.
By using this differential input, small signals common to both
inputs are rejected, as shown in Figure 7, which represents the
typical CMR over frequency. For instance, by using INGND to
sense a remote signal ground, difference of ground potentials
between the sensor and the local ADC ground are eliminated.
70
1
C
–
FREQUENCY
–
kHz
1k
50
30
0
100
60
40
20
10
10
Figure 7. Analog Input CMR vs. Frequency
During the acquisition phase, the impedance of the analog input
IN can be modeled as a parallel combination of capacitor C1
and the network formed by the series connection of R1 and C2.
Capacitor C1 is primarily the pin capacitance. The resistor R1 is
typically 140
and is a lumped component made up of some
serial resistors and the on resistance of the switches. The capacitor
C2 is typically 60 pF and is mainly the ADC sampling capacitor.
During the conversion phase, where the switches are opened, the
input impedance is limited to C1. The R1, C2 makes a one-pole
low-pass filter that reduces undesirable aliasing effect and limits
the noise.
When the source impedance of the driving circuit is low, the
AD7664 can be driven directly. Large source impedances will
significantly affect the ac performances, especially the total
harmonic distortion. The maximum source impedance depends
on the amount of total harmonic distortion (THD) that can be
tolerated. The THD degrades in function of the source imped-
ance and the maximum input frequency as shown in Figure
8.
–
70
10
T
–
FREQUENCY
–
kHz
1k
–
80
–
90
–
100
100
–
75
–
85
–
95
R
S
= 100
R
S
= 50
R
S
= 20
R
S
= 11
Figure 8. THD vs. Analog Input Frequency and
Source Resistance
Driver Amplifier Choice
Although the AD7664 is easy to drive, the driver amplifier needs
to meet at least the following requirements:
The driver amplifier and the AD7664 analog input circuit
have to be able together to settle for a full-scale step the
capacitor array at a 16-bit level (0.0015%). For instance,
operation at the maximum throughput of 570 kSPS requires
a minimum gain bandwidth product of 39 MHz.
The noise generated by the driver amplifier needs to be kept
as low as possible in order to preserve the SNR and transi-
tion noise performance of the AD7664. The noise coming
from the driver is filtered by the AD7664 analog input circuit
one-pole low-pass filter made by R1 and C2. For instance, a
driver such as the AD829, with an equivalent input noise of
2 nV/
√
Hz
and configured as a buffer, thus, with a noise gain
of 1, degrades the SNR by only 0.45 dB. A driver amplifier
with an equivalent input noise of 5 nV/
√
Hz
in the same con-
figuration will add 1.9 dB degradation.
To even further reduce the noise filtering done by the AD7664
analog input circuit, an external simple one-pole RC filter
between the amplifier output and the ADC analog input will
slightly improve the ac performances, specially, the SNR and
the transition noise. For example, as shown in Figure 5, a 15
source resistor with a 2.7 nF good linearity capacitor (NPO or
mica type) limit the bandwidth to 4 MHz.
The driver needs to have a THD performance suitable to that
of the AD7664. TPC 10 gives the THD versus frequency
that the driver should preferably exceed. The AD829 meets
these requirements. The AD829 requires an external compensa-
tion capacitor of 82 pF. This capacitor should have good
linearity as an NPO ceramic or mica or prolypropylene type.
Moreover, the use of a noninverting 1 gain arrangement is
recommended and helps to obtain the best signal-to-noise ratio.
Voltage Reference Input
The AD7664 uses an external 2.5 V voltage reference. The voltage
reference input REF of the AD7664 has a dynamic input imped-
ance. Therefore, it should be driven by a low impedance source
with an efficient decoupling between REF and REFGND inputs.
This decoupling depends on the choice of the voltage reference,
but usually consists of a low ESR tantalum capacitor and a 100 nF
ceramic capacitor. Appropriate value for the tantalum capacitor
is 47
μ
F with the low-cost, low-power ADR291 voltage reference,
or with the low-noise, low-drift AD780 voltage reference. For
applications using multiple AD7664s, it is more effective to buffer
the reference voltage with a low-noise, very stable op amp like
the AD8031.
Care should also be taken with the reference temperature coeffi-
cient of the voltage reference which directly affects the full-scale
accuracy if this parameter matters. For instance, a
±
15 ppm/
°
C
tempco of the reference changes the full scale by
±
1 LSB/
°
C.
Power Supply
The AD7664 uses three sets of power supply pins: an analog 5 V
supply AVDD, a digital 5 V core supply DVDD, and a digital
input/output interface supply OVDD. The OVDD supply allows
direct interface with any logic working between 2.7 V and 5.25 V.
To reduce the number of supplies needed, the digital core
(DVDD) can be supplied through a simple RC filter from the
analog supply as shown in Figure 5. The AD7664 is independent
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD7664ASTRL | 制造商:Analog Devices 功能描述:ADC Single SAR 570ksps 16-bit Parallel/Serial 48-Pin LQFP T/R |
| AD7664ASTZ | 功能描述:IC ADC 16BIT UNIPOLAR 48-LQFP RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:PulSAR® 標(biāo)準(zhǔn)包裝:1 系列:microPOWER™ 位數(shù):8 采樣率（每秒）:1M 數(shù)據(jù)接口:串行，SPI? 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:- 電壓電源:模擬和數(shù)字 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-VQFN 裸露焊盤（4x4） 包裝:Digi-Reel® 輸入數(shù)目和類型:8 個(gè)單端，單極 產(chǎn)品目錄頁面:892 (CN2011-ZH PDF) 其它名稱:296-25851-6 |
| AD7664ASTZRL | 功能描述:IC ADC 16BIT UNIPOLAR 48LQFP RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:PulSAR® 標(biāo)準(zhǔn)包裝:1 系列:- 位數(shù):14 采樣率（每秒）:83k 數(shù)據(jù)接口:串行，并聯(lián) 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:95mW 電壓電源:雙 ± 工作溫度:0°C ~ 70°C 安裝類型:通孔 封裝/外殼:28-DIP（0.600"，15.24mm） 供應(yīng)商設(shè)備封裝:28-PDIP 包裝:管件 輸入數(shù)目和類型:1 個(gè)單端，雙極 |
| AD7664CST | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog to Digital Converter |
| AD7664CSTRL | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog to Digital Converter |
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