```AN-1231
APPLICATION NOTE
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
CIRCUIT FUNCTION AND BENEFITS
VDD1 = +5V
This circuit provides two-quadrant signal multiplication using
converters (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.
1.8pF
VREF
±3.5V
VREF
VDD = +5V
RFB
VDD
SYNC SCLK SDIN
IOUT1
A1
VDD
GND
VSS = –5V
10µF
0.1µF
MICROCONTROLLER
AGND
VSS
10µF
CIRCUIT DESCRIPTION
0.1µF
Figure 2 shows the ac multiplying bandwidth, which is essentially
the frequency response of the DAC when an ac reference is applied
to the VREF input pin. Figure 2 shows that the circuit can handle
a ±3.5 V ac waveform up to approximately 10 MHz.
VOUT = −VREF × (D/2N)
where:
D is the digital word loaded to the DAC.
N is the number of bits: D = 0 to 255 (8-bit AD5426), D = 0 to
VREF can be an ac input signal.
Rev. B | Page 1 of 2
6
0
ZS TO FS
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
–72
–78
–84
–90
–96
–102
1
10
ALL ON
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
ALL OFF
100
1k
10k
100k
FREQUENCY (Hz)
TA = 25°C
VDD = 5V
VREF = ±3.5V
CCOMP = 1.8pF
1M
10M
Figure 2. AC Multiplying Bandwidth Performance
100M
08271-002
current output DACs, 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; however, the supply voltage of the amplifier limits
the output swing. 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 two-quadrant multiplying operation or a unipolar output
voltage swing, as shown in Figure 1. When an output amplifier
is connected in unipolar mode, the output voltage is given by
0.1µF
Figure 1. AC Signal Processing Configuration Using a Multiplying
Current Output DAC (Simplified Schematic)
GAIN (dB)
Description
8-bit/10-bit/12-bit multiplying DACs
Low power, high performance
amplifier
10µF
08271-001
VDD1
Table 1. Devices Connected/Referenced
Product
VOUT = 0V TO –VREF
IOUT2
AN-1231
Application Note
Data Sheets
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.