Datasheet

ManualsBrandsANALOG DEVICES ManualsLinear ICsAD5934YRSZ

250 kSPS, 12-Bit Impedance Converter,

Network Analyzer

Data Sheet

AD5934

Rev. C

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FEATURES

Programmable output peak-to-peak excitation voltage to a

maximum frequency of 100 kHz

Programmable frequency sweep capability with serial I

interface

Frequency resolution of 27 bits (<0.1 Hz)

Impedance measurement range from 1 kΩ to 10 MΩ

Capable of measuring 100 Ω to 1 kΩ with additional circuitry

Phase measurement capability

System accuracy of 0.5%

2.7 V to 5.5 V power supply operation

Temperature range: −40°C to +125°C

16-lead SSOP package

APPLICATIONS

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

GENERAL DESCRIPTION

The AD5934 is a high precision impedance converter system

solution that combines an on-board frequency generator with a

12-bit, 250 kSPS, 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 using the following two equations:

Magnitude =

IR +

Phase = tan

−1

(I/R)

A similar device, available from Analog Devices, Inc., is the

AD5933, which is a 2.7 V to 5.5 V, 1 MSPS, 12-bit impedance

converter, with an internal temperature sensor, available in a

16-lead SSOP.

FUNCTIONAL BLOCK DIAGRAM

ADC

(12 BITS)

VDD/2

DDS

CORE

(27 BITS)

DAC

BIAS

Z(ω)

INTERFACE

IMAGINARY

GAIN

REAL

1024-POINT DFT

LPF

SCL

SDA

DVDDAVDDMCLK

AGND DGND

OUT

VOUT

AD5934

RFB

VIN

05325-001

Figure 1.

Summary of content (32 pages)

PAGE 1
250 kSPS, 12-Bit Impedance Converter, Network Analyzer AD5934 Data Sheet FEATURES GENERAL DESCRIPTION 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 100 Ω to 1 kΩ with additional circuitry Phase measurement capability System accuracy of 0.5% 2.7 V to 5.
PAGE 2
AD5934 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Performing a Frequency Sweep .................................................... 19 Applications ....................................................................................... 1 Register Map ................................................................................... 20 General Description ........................................................
PAGE 3
Data Sheet AD5934 REVISION HISTORY 7/12—Rev. B to Rev. C Changes to Pin 10, Description Column, Table 4 and Pin 11, Description Column, Table 4........................................................... 8 Changes to Table 6 ..........................................................................18 Deleted Choosing a Reference for the AD5934 and Table 17; Renumbered Sequentially ..............................................................30 2/12—Rev. A to Rev. B Deleted Evaluation Board ...............
PAGE 4
AD5934 Data Sheet SPECIFICATIONS VDD = 3.3 V, MCLK = 16.776 MHz, 2 V p-p output excitation voltage @ 30 kHz, 200 kΩ connected between Pin 5 and Pin 6; feedback resistor = 200 kΩ connected between Pin 4 and Pin 5; PGA gain = ×1, unless otherwise noted. Table 1.
PAGE 5
Data Sheet Parameter RECEIVE STAGE Input Leakage Current Input Capacitance 5 Feedback Capacitance, CFB ANALOG-TO-DIGITAL CONVERTER5 Resolution Sampling Rate LOGIC INPUTS Input High Voltage, VIH Input Low Voltage, VIL Input Current 6 Input Capacitance POWER REQUIREMENTS VDD IDD, Normal Mode IDD, Standby Mode IDD, Power-Down Mode AD5934 Min Y Version 1 Typ Max Unit Test Conditions/Comments 1 0.
PAGE 6
AD5934 Data Sheet I2C SERIAL INTERFACE TIMING CHARACTERISTICS VDD = 2.7 V to 5.5 V; all specifications TMIN to TMAX, unless otherwise noted (see Figure 2). Table 2. Parameter 1 fSCL t1 t2 t3 t4 t5 t6 2 Limit at TMIN, TMAX 400 2.5 0.6 1.3 0.6 100 0.9 0 0.6 0.6 1.3 300 0 300 0 250 20 + 0.
PAGE 7
Data Sheet AD5934 ABSOLUTE MAXIMUM RATINGS TA = 25°C, unless otherwise noted. Table 3. Parameter DVDD to GND AVDD1 to GND AVDD2 to GND SDA/SCL to GND VOUT to GND VIN to GND MCLK to GND Operating Temperatures Extended Industrial Range (Y Grade) Storage Temperature Range Maximum Junction Temperature SSOP Package, Thermal Impedance θJA θJC Reflow Soldering (Pb-Free) Peak Temperature Time at Peak Temperature Rating −0.3 V to +7.0 V −0.3 V to +7.0 V −0.3 V to +7.0 V −0.3 V to VDD + 0.3 V −0.3 V to VDD + 0.
PAGE 8
AD5934 Data Sheet NC 1 16 SCL NC 2 15 SDA AD5934 14 AGND2 TOP VIEW (Not to Scale) 13 AGND1 12 DGND VOUT 6 11 AVDD2 NC 7 10 AVDD1 MCLK 8 9 DVDD NC 3 RFB 4 VIN 5 NC = NO CONNECT 05325-003 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS NOTES: 1. IT IS RECOMMENDED TO TIE ALL SUPPLY CONNECTIONS (PIN 9, PIN 10, AND PIN 11) AND RUN FROM A SINGLE SUPPLY BETWEEN 2.7V AND 5.5V. 2. IT IS ALSO RECOMMENDED TO CONNECT ALL GROUND SIGNALS TOGETHER (PIN 12, PIN 13, AND PIN 14). Figure 3.
PAGE 9
Data Sheet AD5934 TYPICAL PERFORMANCE CHARACTERISTICS 35 30 MEAN = 1.9824 SIGMA = 0.0072 MEAN = 0.7543 SIGMA = 0.0099 25 25 NUMBER OF DEVICES 20 15 10 20 15 10 5 0 1.92 05325-064 5 1.94 1.96 1.98 2.00 2.02 2.04 05325-073 NUMBER OF DEVICES 30 0 0.68 2.06 0.70 0.72 0.74 VOLTAGE (V) Figure 4. Range 1 Output Excitation Voltage Distribution, VDD = 3.3 V 0.80 0.82 0.84 0.86 30 MEAN = 0.3827 SIGMA = 0.00167 MEAN = 1.4807 SIGMA = 0.
PAGE 10
AD5934 Data Sheet 15.8 30 MEAN = 0.1982 SIGMA = 0.0008 14.8 14.3 20 IDD (mA) 15 10 13.8 13.3 12.8 12.3 11.8 05325-070 5 0.194 0.196 0.198 0.200 0.202 0.204 05325-088 NUMBER OF DEVICES 25 0 0.192 AVDD1, AVDD2, DVDD CONNECTED TOGETHER OUTPUT EXCITATION FREQUENCY = 30kHz RFB, Z CALIBRATION = 100kΩ 15.3 11.3 10.8 0 0.206 2 4 8 10 12 14 16 18 Figure 12. Typical Supply Current (IDD) vs. MCLK Frequency Figure 10. Range 4 Output Excitation Voltage Distribution, VDD = 3.3 V 0.
PAGE 11
Data Sheet AD5934 TERMINOLOGY Total System Accuracy The AD5934 can accurately measure a range of impedance values to less than 0.5% of the correct impedance value for supply voltages between 2.7 V to 5.5 V. Signal-to-Noise Ratio (SNR) SNR is the ratio of the rms value of the measured output signal to the rms sum of all other spectral components below the Nyquist frequency. The value for SNR is expressed in decibels.
PAGE 12
AD5934 Data Sheet SYSTEM DESCRIPTION MCLK DDS CORE (27 BITS) DAC ROUT COS SIN VOUT VBIAS SCL I2C INTERFACE MICROCONTROLLER SDA Z(ω) AD5934 REAL REGISTER IMAGINARY REGISTER RFB MAC CORE (1024 DFT) PROGRAMMABLE GAIN AMPLIFIER MCLK VIN ADC (12 BITS) LPF ×5 ×1 VDD/2 05325-078 WINDOWING OF DATA Figure 14. Block Overview The AD5934 is a high precision, impedance converter system solution that combines an on-board frequency generator with a 12-bit, 250 kSPS ADC.
PAGE 13
Data Sheet AD5934 TRANSMIT STAGE Frequency Increment As shown in Figure 16, the transmit stage of the AD5934 is made up of a 27-bit phase accumulator DDS core that provides the output excitation signal at a particular frequency. The input to the phase accumulator is taken from the contents of the start frequency register (see Register Address 0x82, Register Address 0x83, and Register Address 0x84).
PAGE 14
AD5934 Data Sheet FREQUENCY SWEEP COMMAND SEQUENCE RECEIVE STAGE The following sequence must be followed to implement a frequency sweep: The receive stage comprises a current-to-voltage amplifier, followed by a programmable gain amplifier (PGA), antialiasing filter, and ADC. The receive stage schematic is shown in Figure 17. The unknown impedance is connected between the VOUT and VIN pins.
PAGE 15
Data Sheet AD5934 IMPEDANCE CALCULATION MAGNITUDE CALCULATION IMPEDANCE CALCULATION USING GAIN FACTOR The first step in the impedance calculation for each frequency point is to calculate the magnitude of the DFT at that point. The next example illustrates how the calculated gain factor derived previously is used to measure an unknown impedance. For this example, assume that the unknown impedance is 510 kΩ.
PAGE 16
AD5934 Data Sheet 2-POINT CALIBRATION GAIN FACTOR SETUP CONFIGURATION Alternatively, it is possible to minimize this error by assuming that the frequency variation is linear and adjusting the gain factor with a 2-point calibration. Figure 19 shows an impedance profile based on a 2-point gain factor calculation. When calculating the gain factor, it is important that the receive stage is operating in its linear region.
PAGE 17
Data Sheet AD5934 GAIN FACTOR TEMPERATURE VARIATION Where the gain factor is given by The typical impedance error variation with temperature is in the order of 30 ppm/°C. Figure 21 shows an impedance profile with a variation in temperature for 100 kΩ impedance using a 2-point gain factor calibration. 101.5 +125°C 100.5 +25°C 100.0 –40°C 99.5 99.0 98.5 54 VDD = 3.3V CALIBRATION FREQUENCY = 60kHz MEASURED CALIBRATION IMPEDANCE = 100kΩ 56 58 60 62 05325-087 IMPEDANCE (kΩ) 101.
PAGE 18
AD5934 Data Sheet As previously outlined, if the user wants to determine the phase angle of the capacitive impedance (ZØ), the user first must determine the system phase response ( ∇system ) and subtract this from the phase calculated with the capacitor connected between VOUT and VIN (Φunknown). Figure 22 shows the AD5934 system phase response calculated using a 220 kΩ calibration resistor (RFB = 220 kΩ, PGA = ×1) and the repeated phase measurement with a 10 pF capacitive impedance.
PAGE 19
Data Sheet AD5934 PERFORMING A FREQUENCY SWEEP PROGRAM FREQUENCY SWEEP PARAMETERS INTO RELEVANT REGISTERS (1) START FREQUENCY REGISTER (2) NUMBER OF INCREMENTS REGISTER (3) FREQUENCY INCREMENT REGISTER PLACE THE AD5934 INTO STANDBY MODE. RESET: BY ISSUING A RESET COMMAND TO THE CONTROL REGISTER, THE DEVICE IS PLACED IN STANDBY MODE. PROGRAM INITIALIZE WITH START FREQUENCY COMMAND TO THE CONTROL REGISTER.
PAGE 20
AD5934 Data Sheet REGISTER MAP Table 7. Register Name Control Register Address 0x80 0x81 0x82 0x83 0x84 0x85 0x86 0x87 0x88 0x89 0x8A 0x8B 0x8F 0x94 0x95 0x96 0x97 Start Frequency Frequency Increment Number of Increments Number of Settling Time Cycles Status Real Data Imaginary Data CONTROL REGISTER (REGISTER ADDRESS 0x80, REGISTER ADDRESS 0x81) The AD5934 contains a 16-bit control register (Register Address 0x80 and Register Address 0x81) that sets the control modes.
PAGE 21
Data Sheet AD5934 Control Register Decode Initialize with Start Frequency This command enables the DDS to output the programmed start frequency for an indefinite time. Initially, it is used to excite the unknown impedance. When the output unknown impedance has settled after a time determined by the user, the user must initiate a start frequency sweep command to begin the frequency sweep.
PAGE 22
AD5934 Data Sheet NUMBER OF INCREMENTS REGISTER (REGISTER ADDRESS 0x88, REGISTER ADDRESS 0x89) The default value of the number of increments register upon reset is as follows: D8 to D0 are not reset at power-up. After a reset command, the contents of this register are not reset. Table 11.
PAGE 23
Data Sheet AD5934 Valid Real/Imaginary Data This bit is set when data processing for the current frequency point is finished, indicating real/imaginary data available for reading. The bit is reset when a start frequency sweep/increment frequency/repeat frequency DDS command is issued. In addition, this bit is reset to 0 when a reset command is issued to the control register. Frequency Sweep Complete This bit is set when data processing for the last frequency point in the sweep is complete.
PAGE 24
AD5934 Data Sheet SERIAL BUS INTERFACE Control of the AD5934 is carried out via the I2C-compliant serial interface protocol. The AD5934 is connected to this bus as a slave device under the control of a master device. The AD5934 has a 7-bit serial bus slave address. When the device is powered up, it has a default serial bus address, 0001101 (0x0D).
PAGE 25
Data Sheet AD5934 WRITING/READING TO THE AD5934 The I2C interface specification defines several different protocols for different types of read and write operations. This section describes the protocols used in the AD5934. The figures in this section use the abbreviations shown in Table 14. Condition Start Stop Read Write Acknowledge No acknowledge write byte/command byte Address Pointer 6. The master sends a data byte (a register address to where the pointer is to point). 7.
PAGE 26
AD5934 Data Sheet READ OPERATIONS Block Read The AD5934 uses two I2C read protocols: the receive byte and the block read. In this operation, the master device reads a block of data from a slave device (see Figure 30). The start address for a block read must previously have been set by setting the address pointer. Receive Byte In the AD5934, the receive byte protocol is used to read a single byte of data from a register address whose address has previously been set by setting the address pointer.
PAGE 27
Data Sheet AD5934 TYPICAL APPLICATIONS MEASURING SMALL IMPEDANCES The AD5934 is capable of measuring impedance values up to 10 MΩ if the system gain settings are chosen correctly for the impedance subrange of interest. If the user places a small impedance value (≤500 Ω over the sweep frequency of interest) between the VOUT and VIN pins, it results in an increase in signal current flowing through the impedance for a fixed excitation voltage in accordance with Ohm’s law.
PAGE 28
AD5934 Data Sheet For example, if the user measures ZUNKNOWN that is known to have a small impedance value within the range of 90 Ω to 110 Ω over the frequency range of 30 kHz to 32 kHz, the user may not be in a position to measure ROUT directly in the factory/lab. Therefore, the user may choose to add on an extra amplifier circuit like that shown in Figure 31 to the signal path of the AD5934.
PAGE 29
Data Sheet AD5934 SENSOR/COMPLEX IMPEDANCE MEASUREMENT ELECTRO-IMPEDANCE SPECTROSCOPY The operational principle of a capacitive proximity sensor is based on the change of a capacitance in a RLC resonant circuit. This leads to changes in the resonant frequency of the RLC circuit, which can be evaluated as shown Figure 33. The AD5934 has found use in the area of corrosion monitoring.
PAGE 30
AD5934 Data Sheet LAYOUT AND CONFIGURATION POWER SUPPLY BYPASSING AND GROUNDING When accuracy is important in a circuit, carefully consider the power supply and ground return layout on the board. The printed circuit board (PCB) containing the AD5934 should have separate analog and digital sections, each having its own area of the board. If the AD5934 is in a system where other devices require an AGND-to-DGND connection, the connection should be made at one point only.
PAGE 31
Data Sheet AD5934 OUTLINE DIMENSIONS 6.50 6.20 5.90 9 16 5.60 5.30 5.00 1 8.20 7.80 7.40 8 0.65 BSC 0.38 0.22 SEATING PLANE 8° 4° 0° 0.95 0.75 0.55 COMPLIANT TO JEDEC STANDARDS MO-150-AC 060106-A 0.05 MIN COPLANARITY 0.10 0.25 0.09 1.85 1.75 1.65 2.00 MAX Figure 34.
PAGE 32
AD5934 Data Sheet NOTES Purchase of licensed I2C components of Analog Devices or one of its sublicensed Associated Companies conveys a license for the purchaser under the Philips I2C Patent Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips. ©2005–2012 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05325-0-7/12(C) Rev.