AD5934 datasheet(11/32 Pages) AD

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AD5934

Rev. 0 | Page 11 of 32

SYSTEM DESCRIPTION

ADC

(12 BITS)

VDD/2

DDS

CORE

(27 BITS)

DAC

ω)

I2C

INTERFACE

IMAGINARY

REAL

MAC CORE

(1024 DFT)

LPF

SCL

SDA

MCLK

ROUT

VOUT

AD5934

RFB

VIN

PROGRAMMABLE

GAIN AMPLIFIER

WINDOWING

OF DATA

COS

SIN

MICROCONTROLLER

MCLK

Figure 14. AD5934 Block Overview

The AD5934 is a high precision impedance converter system

solution which combines an on-board frequency generator with a

12-bit, 250 kSPS 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 DFT processed by an on-board DSP engine. The DFT

algorithm returns both a real (R) and imaginary (I) data-word at

each frequency point along the sweep. The impedance magnitude

and phase is easily calculated using the following equations:

Magnitude

)

(

Tan

Phase

−

To characterize an impedance profile Z(ω), generally a frequency

sweep is required like that shown in Figure 15.

FREQUENCY

Figure 15.

The AD5934 permits the user to perform a frequency sweep with

a user-defined start frequency, frequency resolution, and number

of points in the sweep. In addition, the device allows the user to

program the peak-to-peak value of the output sinusoidal signal as

an excitation to the external unknown impedance connected

between the VOUT and VIN pins.

Table 6 gives the four possible output peak-to-peak voltages and

the corresponding dc bias levels for each range.

Table 6.

Output Excitation Voltage Amplitude

Output DC Bias Level

Range 1: 1.98 V p-p

1.48 V

Range 2: 0.99 V p-p

0.74V

Range 3: 383 mV p-p

0.31 V

Range 4: 198 mV p-p

0.179 V

The excitation signal for the transmit stage is provided on-chip

using DDS techniques which permit subhertz resolution. The

receive stage receives the input signal current from the unknown

impedance, performs signal processing, and digitizes the result.

The clock for the DDS is generated from an external reference

clock which is provided by the user at MCLK.

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