CN-0217 Datasheet, PDF (1/6 Pages) Analog Devices – High Accuracy Impedance Measurements Using 12-Bit Impedance Converters

Circuit Note
CN-0217
Circuits from the Lab™ reference circuits are engineered and
tested for quick and easy system integration to help solve today’s
analog, mixed-signal, and RF design challenges. For more
information and/or support, visit www.analog.com/CN0217.
Devices Connected/Referenced
AD5933
1 MSPS, 12-Bit Impedance Converter,
Network Analyzer
AD5934
250 kSPS, 12-Bit Impedance Converter,
Network Analyzer
AD8606 Precision, Low Noise, Dual CMOS Op Amp
High Accuracy Impedance Measurements Using 12-Bit Impedance Converters
EVALUATION AND DESIGN SUPPORT
Circuit Evaluation Boards
AD5933 Evaluation Board (EVAL-AD5933EBZ)
Design and Integration Files
Schematics, Layout Files, Bill of Materials
MCLK
V_DD
AVDD
V_DD
DVDD
OSCILLATOR
SCL
SDA
I²C
INTERFACE
REAL IMAGINARY
REGISTER REGISTER
1024-POINT DFT
DDS
CORE
(27 BITS)
DAC
TEMPERATURE
SENSOR
AD5933/AD5934
AGND
ADC
(12 BITS)
DGND
GAIN
LPF
CIRCUIT FUNCTION AND BENEFITS
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 it also optimizes the overall accuracy of the
AD5933/AD5934.
1.98V p-p
1.98V p-p
1.48V
V_DD/2
R_OUT
TRANSMIT SIDE
OUTPUT AMPLIFIER
V_DD
VOUT
47nF
50kΩ
50kΩ
V_DD
−
A1
+
A1, A2 ARE
½ AD8606
RFB
R_FB
20kΩ
VIN
20kΩ
−
A2
I-V
+
V_DD
Z_UNKNOWN
VDD/2
50kΩ
50kΩ
Figure 1. Optimized Signal Chain for Impedance Measurement Accuracy (Simplified Schematic, All Connections and Decoupling Not Shown)
Rev. A
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