ADI公司的高精度阻抗测量解决方案CN0217采用12位阻抗转换器AD5933/AD5934. AD5933是1MSPS的12位ADC,而AD5934是250KSPS的12位ADC,内部集成了温度传感器(±2°C),系统精度0.5%,工作电压2.7V-5.5V,图1的电路优化了信号链,其阻抗测量范围从低欧姆数到几百kΩ,主要用在电化学分析,生物阻抗分析,复数阻抗分析,生物和汽车传感器,接近式检测,非破坏性检测,以及材料特性分析和燃料/电池状态监视等.本文介绍了AD5933主要特性, 功能方框图, 病毒株血样本测量框图和AD5933评估板主要特性,电路图与材料清单.

The AD5933 and AD5934 are high precision impedance converter system solutions that combine an on-chip programmable frequency generator with a 12-bit, 1 MSPS (AD5933) or 250 kSPS (AD5934) analog-to-digital converter (ADC). The tunable frequency generator allows an external complex impedance to be excited with a known frequency.

The circuit shown in Figure 1 yields accurate impedance measurements extending from the low ohm range to several hundred kΩ and also optimizes the overall accuracy of the AD5933/AD5934.

图1.高精度阻抗测量优化信号链的电路图

The AD5933 is a high precision impedance converter system solution that combines an on-board frequency generator with a 12-bit, 1 MSPS, analog-to-digital converter (ADC). The frequency generator allows an external complex impedance to be excited with a known frequency. The response signal from the impedance is sampled by the on-board ADC and a discrete Fourier transform (DFT) is processed by an on-board DSP engine. The DFT algorithm returns a real (R) and imaginary (I) data-word at each output frequency.

Once calibrated, the magnitude of the impedance and relative phase of the impedance at each frequency point along the sweep is easily calculated. This is done off chip using the real and imaginary register contents, which can be read from the serial I2C interface.

A similar device, also available from Analog Devices, Inc., is the AD5934, a 2.7 V to 5.5 V, 250 kSPS, 12-bit impedance converter, with an internal temperature sensor and is packaged in a 16-lead SSOP.

AD5933主要特性:

Programmable output peak-to-peak excitation voltage to a maximum frequency of 100 kHz

Programmable frequency sweep capability with serial I2C interface

Frequency resolution of 27 bits (<0.1 Hz)

Impedance measurement range from 1 kΩ to 10 MΩ

Capable of measuring of 100 Ω to 1 kΩ with additional circuitry

Internal temperature sensor (±2℃)

Internal system clock option

Phase measurement capability

System accuracy of 0.5%

2.7 V to 5.5 V power supply operation

Temperature range: −40℃ to +125℃

16-lead SSOP package

AD5933应用:

Electrochemical analysis

Bioelectrical impedance analysis

Impedance spectroscopy

Complex impedance measurement

Corrosion monitoring and protection equipment

Biomedical and automotive sensors

Proximity sensing

Nondestructive testing

Material property analysis

Fuel/battery cell condition monitoring

图2. AD5933功能方框图

图3. 采用AD5933的病毒株血样本测量框图

AD5933评估板

This document describes the evaluation board for the AD5933 and the application software developed to interface to the device.

The AD5933 is a high precision impedance converter system that combines an on-board frequency generator with a 12-bit, 1 MSPS ADC. The frequency generator allows an external complex impedance to be excited with a known frequency. The response signal from the impedance is sampled by the on-board ADC, and the DFT is processed by an on-board DSP engine at each excitation frequency. The AD5933 also contains an internal temperature sensor with 13-bit resolution and operates from a 2.7 V to 5.5 V supply.

Other on-board components include an ADR423 3.0 V reference that acts as a stable supply voltage for the separate analog and digital sections of the device and an ADP3303 ultrahigh precision regulator that acts as a supply to the on-board universal serial bus controller, which interfaces to the AD5933. The user can power the entire circuitry from the USB port of a computer. The evaluation board also has a high performance, trimmed, 16 MHz, surface-mount crystal that can act as a system clock for the AD5933, if required.

The various link options available on the evaluation board are explained in Table 2. Interfacing to the AD5933 is through a USB microcontroller, which generates the I²C signals necessary to communicate with the AD5933.The user interfaces to the USB microcontroller through a Visual Basic® graphic user interface located on and run from the user PC. More information on the AD5933 is available from Analog Devices, Inc., at www.analog.com and should be consulted when using the evaluation board.

AD5933评估板主要特性:

Full-featured evaluation board for the AD5933

Graphic user interface software with frequency sweep capability for board control and data analysis

Various power supply linking options

Standalone capability with serial I²C loading from on-board microcontroller

Selectable system clock options, including internal RC oscillator or on-board 16 MHz crystal

AD5933评估板应用:

Electrochemical analysis

Impedance spectroscopy

Complex impedance measurement

Corrosion monitoring and protection equipment

Biomedical and automotive sensors

Proximity sensing


图4.AD5933评估板方框图

图5. EVAL-CN0217-EBIZ电路图(1)

图6. EVAL-CN0217-EBIZ电路图(2)

图7. EVAL-CN0217-EBIZ电路图(3)

EVAL-CN0217-EBIZ材料清单(BOM)见:
EVAL-CN0217-EBIZ材料清单.xls

详情请见:
http://www.analog.com/static/imported-files/circuit_notes/CN0217.pdf
和
http://www.analog.com/static/imported-files/data_sheets/AD5933.pdf
以及
http://www.analog.com/static/imported-files/eval_boards/537700023EVAL_AD5933EB.pdf