ADI公司的高精度阻抗測量解決方案CN0217采用12位阻抗轉換器AD5933/AD5934. AD5933是1MSPS的12位ADC,而AD5934是250KSPS的12位ADC,內部集成了溫度傳感器(±2°C),系統精度0.5%,工作電壓2.7V-5.5V,圖1的電路優化了信號鏈,其阻抗測量范圍從低歐姆數到幾百kΩ,主要用在電化學分析,生物阻抗分析,復數阻抗分析,生物和汽車傳感器,接近式檢測,非破壞性檢測,以及材料特性分析和燃料/電池狀態監視等.本文介紹了AD5933主要特性, 功能方框圖, 病毒株血樣本測量框圖和AD5933評估板主要特性,電路圖與材料清單.
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.
圖1.高精度阻抗測量優化信號鏈的電路圖
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應用:
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
圖2. AD5933功能方框圖
圖3. 采用AD5933的病毒株血樣本測量框圖
AD5933評估板
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評估板主要特性:
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評估板應用:
Electrochemical analysis
Impedance spectroscopy
Complex impedance measurement
Corrosion monitoring and protection equipment
Biomedical and automotive sensors
Proximity sensing
圖4.AD5933評估板方框圖
圖5. EVAL-CN0217-EBIZ電路圖(1)
圖6. EVAL-CN0217-EBIZ電路圖(2)
圖7. EVAL-CN0217-EBIZ電路圖(3)
EVAL-CN0217-EBIZ材料清單(BOM)見:
EVAL-CN0217-EBIZ材料清單.xls
詳情請見:
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
