AD7699 SAR 模数转换方案

数据采集设计工程师面临的挑战是设计具有最高的精度、最高的集成度以及最低的功耗解决方案，因此多通道ADC已经成为越来越受欢迎的选择。ADI 公司的AD7699 是最快的16位8通道SAR 模数转换器，采样速率500 kSPS，广泛应用在以电池为能源的设备，医疗仪器，移动通信，PDA，数据采集以及过程控制等。本文介绍一系列模数转换器的特性，集中介绍了AD7699的主要性能特点，方框图以及评估板的详细电路图。

多通道ADC降低功耗和空间需求
数据采集设计工程师面临的挑战是设计具有最高的精度、最高的集成度以及最低的功耗解决方案，因此多通道ADC已经成为越来越受欢迎的选择。AD768x 系列14 bit与16 bit ADC不仅能够满足这些需求，而且能够进一步缩短设计周期。AD7699是最快的16 bit、8通道ADC，采样速率500 kSPS。AD7682与AD7689工作电压是2.7 V，以节省功耗。AD7949是低成本的14 bit、8通道ADC。其他系列特性包括：允许单端、差分或双极输入的可配置多路复用器、可选择电压基准（2.5 V或4.096 V）、温度传感器、可选择单极滤波器、允许连续的通道扫描的时序器。适合AD768x系列产品的驱动放大器包括ADA4841-2、AD8021与AD8022。

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24位过采样ADC，适合低功耗设备
ADI公司的24位过采样ADC的设计目的是扩展Σ-Δ产品系列，使其速率超过工业类型Σ-Δ ADC的输出数据速率。
这些ADC实现了宽动态范围与输入带宽（如AD7766与AD7767）与适合高端仪器应用的低功耗（如振动分析、声纳与音频）等特性的完美结合。在较大交流或直流信号中测量输入信号的微小变化时，AD776x产品系列是完美的设计选择。 适合AD776x系列的ADI配套产品包括ADA4841，它是低噪声与低失真度、轨对轨输出放大器，以及低功耗、低失真度、高信噪比驱动器放大器ADA4941。

The AD7699 is an 8-channel 16-bit, charge redistribution successive approximation register (SAR), analog-to-digital converter (ADC) that operates from a single power supply, VDD.
The AD7699 contains all of the components for use in a multichannel, low power, data acquisition system including: a true 16-bit SAR ADC with no missing codes; an 8-channel, low crosstalk
multiplexer useful for configuring the inputs as single ended (with or without ground sense), differential or bipolar; an internal low drift reference (selectable 2.5V or 4.096V) and buffer; a temperature sensor; a selectable 1-pole filter; and a sequencer useful when channels are continuously scanned in order.
The AD7699 uses a simple SPI interface for writing to the configuration register and receiving conversion results. The SPI interface uses a separate supply, VIO, which is set to the host logic
level.Power dissipation scales with throughput.
The AD7699 is housed in a tiny 20-lead LFCSP with operation specified from ?40°C to +85°C.
AD7699主要特性：
16-bit resolution with no missing codes
4-channel multiplexer with:
Unipolar single ended or
Differential (GND sense)/pseudo-bipolar inputs
Throughput: 500 kSPS
INL/DNL: ±0.6 LSB typical
Dynamic range: 93.5 dB
SINAD: 92.5 dB @ 20 kHz
THD: ?100 dB @ 20 kHz
Analog input range:
0 V to VREF with VREF up to VDD
Reference:
Internal selectable 2.5 V/4.096 V or
External buffered (up to 4.096 V)
External (up to VDD)
Internal temperature sensor
Channel sequencer, selectable 1-pole filter, BUSY indicator
No pipeline delay, SAR architecture
Single-supply 5 V operation with
1.8 V to 5 V logic interface
Serial interface SPI®/QSPI/MICROWIRE/DSP compatible
Power dissipation:
6 mW @ 5 V/100 kSPS
Standby current: 1 nA
20-lead 4 mm × 4 mm LFCSP package
主要应用：
Battery-powered equipment
Medical instruments
Mobile communications
Personal digital assitants
Data acquisition
Seismic data acquisition systems
Instrumentation
Process Control

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图1. AD7699方框图
The EVAL-AD76XXCB 8/10-Pin is an evaluation board for the AD768x/AD769x/AD794x/AD798x 8 and 10-pin PulSAR high resolution ADCs
评估板主要特性：
Versatile analog signal conditioning circuitry
On-board reference, crystal oscillator and buffers
16-bit Parallel Buffered Outputs
Ideal for DSP and data acquisition card interfaces
Analog and digital prototyping area for breadbording the target system
Stand-alone operation or Eval control board compatibility
PC software for control and data analysis
LabVIEW1 driver to develop custom application

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图2.评估板外形图

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图3. 评估板电路图（模拟部分）

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图4. 评估板电路图（数字部分）

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图5. 评估板电路图（电源部分）

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