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參數(shù)資料
| 型號： | AD9244BST-65 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | 14-Bit, 40/65 MSPS Monolithic A/D Converter |
| 中文描述： | 1-CH 14-BIT FLASH METHOD ADC, PARALLEL ACCESS, PQFP48 |
| 封裝： | MS-026-BBC, LQFP-48 |
| 文件頁數(shù)： | 17/36頁 |
| 文件大?。?/td> | 1845K |
| 代理商： | AD9244BST-65 |
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REV. A
AD9244
–17–
The optimum noise and dc linearity performance for either
differential or single-ended inputs is achieved with the largest
input signal voltage span (i.e., 2 V input span) and matched
input impedance for VIN+ and VIN
–
. Only a slight degradation
in dc linearity performance exists between the 2 V and 1 V input
spans; however, the SNR is lower in the 1 V input span.
When the ADC is driven by an op amp and a capacitive load is
switched onto the output of the op amp, the output will momen-
tarily drop due to its effective output impedance. As the output
recovers, ringing may occur. To remedy the situation, a series
resistor, R
S
, can be inserted between the op amp and the SHA
input as shown in Figure 6. A shunt capacitance also acts like
a charge reservoir, sinking or sourcing the additional charge
required by the sampling capacitor, C
S
, further reducing current
transients seen at the op amp
’
s output.
AD9244
VIN+
VIN–
VREF
SENSE
REFCOM
V
CC
V
EE
R
S
33
R
S
33
20pF
10 F
0.1 F
+
Figure 6. Resistors Isolating SHA Input from Op Amp
The optimum size of this resistor is dependent on several factors,
including the ADC sampling rate, the selected op amp, and the
particular application. In most applications, a 30
to 100
resistor is sufficient.
For noise sensitive applications, the very high bandwidth of the
AD9244 may be detrimental and the addition of a series resistor
and/or shunt capacitor can help limit the wideband noise at the
ADC
’
s input by forming a low-pass filter. The source impedance
driving VIN+ and VIN
–
should be matched. Failure to provide
matching may result in degradation of the SNR, THD, and
SFDR performance.
Differentially Driving the Analog Inputs
The AD9244 has a very flexible input structure, allowing it to
interface with single-ended or differential inputs.
The optimum mode of operation, analog input range, and
associated interface circuitry will be determined by the particular
application
’
s performance requirements as well as power supply
options.
Differential operation requires that VIN+ and VIN
–
be simulta-
neously driven with two equal signals that are 180
°
out of phase
with each other.
Differential modes of operation (ac-coupled or dc-coupled input)
provide the best SFDR performance over a wide frequency range.
They should be considered for the most demanding spectral-based
applications (i.e., direct IF conversion to digital).
Since not all applications have a signal precondition for differential
operation, there is often a need to perform a single-ended-to-
differential conversion. In systems that do not require dc coupling,
an RF transformer with a center tap is the best method for
generating differential input signals for the AD9244. This provides
the benefit of operating the ADC in the differential mode without
contributing additional noise or distortion. An RF transformer
also has the added benefit of providing electrical isolation between
the signal source and the ADC.
The differential input characterization for this data sheet was
performed using the configuration in Figure 7. The circuit uses
a Mini-Circuits
RF transformer, model T1
–
1T, which has an
impedance ratio of 1:1. This circuit assumes that the signal source
has a 50
source impedance. The secondary center tap of the
transformer allows a dc common-mode voltage to be added to
the differential input signal. In Figure 7, the center tap is con-
nected to a resistor divider providing a half supply voltage. It could
also be connected to the CML pin of the AD9244. It is recom-
mended for IF sampling applications (70 MHz < f
IN
< 200 MHz)
that the 20 pF differential capacitor between VIN+ and VIN
–
be reduced or removed.
REFT
REFB
AD9244
VIN+
VIN–
1k
0.1 F
0.1 F
0.1 F
10 F
1k
50
AVDD
0.1 F
R
S
33
MINI-CIRCUITS
T1–1T
R
S
33
20pF
+
Figure 7. Transformer-Coupled Input
The circuit shown in Figure 8 shows a method for applying a
differential direct-coupled signal to the AD9244. An AD8138
amplifier is used to derive a differential signal from a single-
ended signal.
REFT
REFB
AD8138
AD9244
VIN+
VIN–
1k
5V
0.1 F
0.1 F
0.1 F
10 F
499
50
1V p-p
0V
AVDD
10 F
+
0.1 F
10 F
0.1 F
0.1 F
499
499
475
1k
20pF
33
33
+
+
Figure 8. Direct-Coupled Drive Circuit with AD8138
Differential Op Amp
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD9244BSTRL-40 | 制造商:AD 制造商全稱:Analog Devices 功能描述:14-Bit, 40/65 MSPS Monolithic A/D Converter |
| AD9244BSTRL-65 | 制造商:Analog Devices 功能描述:Single ADC Pipelined 65Msps 14-bit Parallel 48-Pin LQFP T/R |
| AD9244BSTZ40 | 制造商:Analog Devices 功能描述: |
| AD9244BSTZ-40 | 功能描述:IC ADC 14BIT 40MSPS 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:- 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 |
| AD9244BSTZ-401 | 制造商:AD 制造商全稱:Analog Devices 功能描述:14-Bit, 40 MSPS/65 MSPS A/D Converter |
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