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參數資料
| 型號： | AD9238 |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | ADC |
| 英文描述： | 12-Bit, 20/40/65 MSPS Dual A/D Converter |
| 中文描述： | 12位，20/40/65 MSPS雙通道的A / D轉換器 |
| 文件頁數： | 12/24頁 |
| 文件大小： | 1737K |
| 代理商： | AD9238 |
AD9238
Equivalent Circuits
–12–
AVDD
VIN+_A, VIN–_A,
VIN+_B, VIN–_B,
Figure 2. Equivalent Analog Input Circuit
Figure 3. Equivalent Digital Output Circuit
AVDD
CLK_A, CLK_B
DCS, DFS,
MUX_SELECT
SHARED_REF
THEORY OF OPERATION
The AD9238 consists of two high performance analog-to-digital
converters (ADCs) that are based on the AD9235 converter core.
The dual ADC paths are independent, except for a shared internal
band gap reference source, V
REF
. Each of the ADC’s paths consists
of a proprietary front end sample-and-hold amplifier (SHA)
followed by a pipelined switched capacitor ADC. The pipelined
ADC is divided into three sections, consisting of a 4-bit first stage
followed by eight 1.5-bit stages and a final 3-bit flash. Each stage
provides sufficient overlap to correct for flash errors in the preced-
ing stages. The quantized outputs from each stage are combined
through the digital correction logic block into a final 12-bit result.
The pipelined architecture permits the first stage to operate on a
new input sample, while the remaining stages operate on preceding
samples. Sampling occurs on the rising edge of the respective clock.
Each stage of the pipeline, excluding the last, consists of a low
resolution flash ADC and a residual multiplier to drive the next
stage of the pipeline. The residual multiplier uses the flash ADC
output to control a switched capacitor digital-to-analog converter
(DAC) of the same resolution. The DAC output is subtracted from
the stage’s input signal and the residual is amplified (multiplied)
to drive the next pipeline stage. The residual multiplier stage is
also called a multiplying DAC (MDAC). One bit of redundancy
is used in each one of the stages to facilitate digital correction of
flash errors. The last stage simply consists of a flash ADC.
The input stage contains a differential SHA that can be config-
ured as ac- or dc-coupled in differential or single-ended modes.
The output-staging block aligns the data, carries out the error
correction, and passes the data to the output buffers. The output
buffers are powered from a separate supply, allowing adjustment
of the output voltage swing.
ANALOG INPUT
The analog input to the AD9238 is a differential switched capacitor,
SHA, that has been designed for optimum performance while
processing a differential input signal. The SHA input accepts inputs
over a wide common-mode range. An input common-mode voltage
of midsupply is recommended to maintain optimal performance.
The SHA input is a differential switched capacitor circuit. In
Figure 5, the clock signal alternatively switches the SHA between
sample mode and hold mode. When the SHA is switched into
sample mode, the signal source must be capable of charging the
sample capacitors and settling within one-half of a clock cycle. A
small resistor in series with each input can help reduce the peak
transient current required from the output stage of the driving
source. Also, a small shunt capacitor can be placed across the inputs
to provide dynamic charging currents. This passive network will
create a low-pass filter at the ADC’s input; therefore, the precise
values are dependant on the application. In IF undersampling
applications, any shunt capacitors should be removed. In combi-
nation with the driving source impedance, they would limit the
input bandwidth. For best dynamic performance, the source
impedances driving VIN+ and VIN– should be matched such that
common-mode settling errors are symmetrical. These errors will
be reduced by the common-mode rejection of the ADC.
REV. A
相關PDF資料 |
PDF描述 |
|---|---|
| AD9238BST-20 | TV07RW21-35SD W/ PC CONT |
| AD9238BST-40 | 12-Bit, 20/40/65 MSPS Dual A/D Converter |
| AD9238BST-65 | 12-Bit, 20/40/65 MSPS Dual A/D Converter |
| AD9238BSTRL-20 | 12-Bit, 20/40/65 MSPS Dual A/D Converter |
| AD9238BSTRL-40 | 12-Bit, 20/40/65 MSPS Dual A/D Converter |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD9238_05 | 制造商:AD 制造商全稱:Analog Devices 功能描述:12-Bit, 20 MSPS/40 MSPS/65 MSPS Dual A/D Converter |
| AD9238BCP-20EB | 制造商:Analog Devices 功能描述: |
| AD9238BCP-20EBZ | 制造商:Analog Devices 功能描述:EVALUATION BOARD FOR AD9238 DUAL A/D CONVERTER ,12-BIT, 20 MSPS/40 MSPS/65 MSPS 制造商:Analog Devices 功能描述:EVAL BD FOR AD9238 DUAL A/D CNVRTR ,12-BIT, 20 MSPS/40 MSPS/ - Bulk |
| AD9238BCP-40EB | 制造商:Analog Devices 功能描述:EVAL BD FOR AD9238 DUAL A/D CNVRTR ,12-BIT, 20 MSPS/40 MSPS/ - Bulk |
| AD9238BCP-40EBZ | 制造商:Analog Devices 功能描述:EVAL BD FOR AD9238 DUAL A/D CNVRTR ,12-BIT, 20 MSPS/40 MSPS/ - Bulk |
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