This circuit provides 2-quadrant signal multiplication using the
AD5426/AD5432/AD5443 current output DACs and an operational amplifier. It provides multiplying bandwidth up to
10 MHz, which allows accurate conditioning of ac signals with bandwidths up to this frequency. The circuit is well suited for ac signal conditioning applications in communications, industrial, and medical applications.
The AD5426, AD5432, and AD5443 are CMOS 8-bit/10-bit/
12-bit current output digital-to-analog converters, respectively.
These devices operate from a 2.5 V to 5.5 V power supply, making them suitable for battery powered applications, signal attenuation, channel equalization, and waveform generation.
The maximum signal range can be up to ±12 V, but the output
swing is limited by the supply voltage of the amplifier. Figure 1
shows a typical application circuit for a current output DAC for ac signal processing. Using a single op amp, these devices can easily be configured to provide either a 2-quadrant multiplying operation or a unipolar output voltage swing, as shown in
Figure 1. When an output amplifier is connected in the unipolar
mode, the output voltage is given by
V
OUT
= − V
REF
× (D/2 N ) where D is the digital word loaded to the DAC and N is the number of bits: D = 0 to 255 (8-bit AD5426); D = 0 to 1023
(10-bit AD5432); and D = 0 to 4095 (12-bit AD5443). V
REF
can
be an ac input signal. Figure 2 shows the ac multiplying
bandwidth, which is essentially the frequency response of the
DAC when an ac reference is applied to the V
REF
input pin. The plot shows that the circuit can handle a ±3.5 V ac waveform up to approximately 10 MHz.
V
DD1
= +5V
V
DD
= +5V
V
REF
±3.5V
V
DD
V
REF
AD5426/
AD5432/
AD5443
SYNC SCLK SDIN
1.8pF
R
FB
I
OUT
1
I
OUT
2
GND
MICROCONTROLLER
V
SS
= –5V
V
OUT
= 0V TO –V
REF
V
DD
10µF 0.1µF
AGND V
SS
10µF 0.1µF
10µF
V
DD1
0.1µF
Figure 1. AC Signal Processing Configuration Using a Multiplying
Current Output DAC (Simplified Schematic)
–36
–42
–48
–54
–60
–66
–72
–78
–6
–12
6
0
–18
–24
–30
–84
–90
–96
–102
1
LOADING
ZS TO FS
10
ALL ON
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
ALL OFF
100 1k 10k 100k
C
V
T
V
DD
REF
A
= 25°C
= 5V
= ±3.5V
COMP
= 1.8pF
AD8038 AMPLIFIER
1M 10M
FREQUENCY (Hz)
Figure 2. AC Multiplying Bandwidth Performance
100M

ADIsimPower Design Tool. Analog Devices
Kester, Walt. 2005.The Data Conversion Handbook. Analog
Devices. Chapters 3 and 7.
MT-015 Tutorial, Basic DAC Architectures II: Binary DACs .
Analog Devices.
MT-031 Tutorial, Grounding Data Converters and Solving the
Mystery of AGND and DGND . Analog Devices.
MT-033 Tutorial, Voltage Feedback Op Amp Gain and
Bandwidth . Analog Devices.
MT-035 Tutorial, Op Amp Inputs, Outputs, Single-Supply, and
Rail-to-Rail Issues . Analog Devices.
MT-101 Tutorial, Decoupling Techniques . Analog Devices.
Voltage Reference Wizard Design Tool. Analog Devices.
Data Sheets
AD5426 Data Sheet.
AD5432 Data Sheet.
AD5443 Data Sheet.
AD8038 Data Sheet.
7/09—Rev. 0 to Rev. A
Updated Format .................................................................. Universal
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