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| 型号： | AD9258BCPZ-125 |
| 厂商： | Analog Devices Inc |
| 文件页数： | 19/44页 |
| 文件大小： | 0K |
| 描述： | IC ADC 14BIT 125MSPS DL 64LFCSP |
| 设计资源： | High Performance, Dual Channel IF Sampling Receiver (CN0140) |
| 标准包装： | 1 |
| 位数： | 14 |
| 采样率（每秒）： | 125M |
| 数据接口： | 串行 |
| 转换器数目： | 2 |
| 功率耗散（最大）： | 788mW |
| 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： | 64-VFQFN 裸露焊盘，CSP |
| 供应商设备封装： | 64-LFCSP-VQ（9x9） |
| 包装： | 托盘 |
| 输入数目和类型： | 2 个差分，单极 |
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AD9258
Rev. A | Page 26 of 44
THEORY OF OPERATION
The AD9258 dual-core analog-to-digital converter (ADC)
design can be used for diversity reception of signals, in which the
ADCs are operating identically on the same carrier but from two
separate antennae. The ADCs can also be operated with inde-
pendent analog inputs. The user can sample any fS/2 frequency
segment from dc to 200 MHz, using appropriate low-pass or
band-pass filtering at the ADC inputs with little loss in ADC
performance. Operation to 300 MHz analog input is permitted
but occurs at the expense of increased ADC noise and distortion.
In nondiversity applications, the AD9258 can be used as a base-
band or direct downconversion receiver, in which one ADC is
used for I input data, and the other is used for Q input data.
Synchronization capability is provided to allow synchronized
timing between multiple devices.
Programming and control of the AD9258 are accomplished
using a 3-wire SPI-compatible serial interface.
ADC ARCHITECTURE
The AD9258 architecture consists of a dual front-end sample-
and-hold circuit, followed by a pipelined, switched-capacitor
ADC. The quantized outputs from each stage are combined into
a final 14-bit result in the digital correction logic. The pipelined
architecture permits the first stage to operate on a new input
sample and the remaining stages to operate on the preceding
samples. Sampling occurs on the rising edge of the clock.
Each stage of the pipeline, excluding the last, consists of a low
resolution flash ADC connected to a switched-capacitor digital-
to-analog converter (DAC) and an interstage residue amplifier
(MDAC). The MDAC magnifies the difference between the recon-
structed DAC output and the flash input for the next stage in
the pipeline. One bit of redundancy is used in each stage to
facilitate digital correction of flash errors. The last stage simply
consists of a flash ADC.
The input stage of each channel contains a differential sampling
circuit that can be ac- or dc-coupled in differential or single-
ended modes. The output staging block aligns the data, corrects
errors, and passes the data to the output buffers. The output buffers
are powered from a separate supply, allowing digital output noise to
be separated from the analog core. During power-down, the
output buffers go into a high impedance state.
ANALOG INPUT CONSIDERATIONS
The analog input to the AD9258 is a differential switched-
capacitor circuit that has been designed for optimum performance
while processing a differential input signal.
The clock signal alternatively switches the input between sample
mode and hold mode (see Figure 64). When the input is switched
into sample mode, the signal source must be capable of charging
the sample capacitors and settling within 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. A shunt capacitor can be placed across the
inputs to provide dynamic charging currents. This passive
network creates a low-pass filter at the ADC input; therefore,
the precise values are dependent on the application.
In intermediate frequency (IF) undersampling applications, any
shunt capacitors should be reduced. In combination with the
driving source impedance, the shunt capacitors limit the input
bandwidth. Refer to the AN-742 Application Note, Frequency
Domain Response of Switched-Capacitor ADCs; the AN-827
Application Note, A Resonant Approach to Interfacing Amplifiers to
Switched-Capacitor ADCs; and the Analog Dialogue article,
for more information on this subject (refer to www.analog.com).
CPAR1
CPAR2
S
CFB
CS
BIAS
VIN+
0
812
4-
0
34
H
VIN–
Figure 64. Switched-Capacitor Input
For best dynamic performance, the source impedances driving
VIN+ and VIN should be matched, and the inputs should be
differentially balanced.
An internal differential reference buffer creates positive and
negative reference voltages that define the input span of the ADC
core. The span of the ADC core is set by this buffer to 2 × VREF.
Input Common Mode
The analog inputs of the AD9258 are not internally dc biased.
In ac-coupled applications, the user must provide this bias
externally. Setting the device so that VCM = 0.5 × AVDD (or
0.9 V) is recommended for optimum performance, but the
device functions over a wider range with reasonable perfor-
mance (see Figure 54). An on-board common-mode voltage
reference is included in the design and is available from the
VCM pin. Optimum performance is achieved when the
common-mode voltage of the analog input is set by the VCM
pin voltage (typically 0.5 × AVDD). The VCM pin must be
decoupled to ground by a 0.1 μF capacitor, as described in the
Applications Information section.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| AD9258BCPZ-1251 | 制造商:AD 制造商全称:Analog Devices 功能描述:14-Bit, 80 MSPS/105 MSPS/125 MSPS, 1.8 V Dual Analog-to-Digital Converter (ADC) |
| AD9258BCPZ-80 | 功能描述:模数转换器 - ADC Dual 14 bit 80 high SNR ADC RoHS:否 制造商:Analog Devices 通道数量: 结构: 转换速率: 分辨率: 输入类型: 信噪比: 接口类型: 工作电源电压: 最大工作温度: 安装风格: 封装 / 箱体: |
| AD9258BCPZ-801 | 制造商:AD 制造商全称:Analog Devices 功能描述:14-Bit, 80 MSPS/105 MSPS/125 MSPS, 1.8 V Dual Analog-to-Digital Converter (ADC) |
| AD9258BCPZRL7-105 | 功能描述:模数转换器 - ADC Dual 14 bit 105 highSNR ADC RoHS:否 制造商:Analog Devices 通道数量: 结构: 转换速率: 分辨率: 输入类型: 信噪比: 接口类型: 工作电源电压: 最大工作温度: 安装风格: 封装 / 箱体: |
| AD9258BCPZRL7-1051 | 制造商:AD 制造商全称:Analog Devices 功能描述:14-Bit, 80 MSPS/105 MSPS/125 MSPS, 1.8 V Dual Analog-to-Digital Converter (ADC) |
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