AN-732 Datasheet, PDF (1/4 Pages) Analog Devices – Universal Precision Op Amp Evaluation Board in SOIC Package

AN-732
APPLICATION NOTE
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • Tel: [phone] • Fax: [phone] • www.analog.com
Universal Precision Op Amp Evaluation Board in SOIC Package
by Giampaolo Marino, Soufiane Bendaoud, and Steve Ranta
INTRODUCTION
The EVAL-PRAOPAMP-1R is an evaluation board which
accommodates single op amps in SOIC packages. It is
meant to provide the user with multiple choices and
extensive flexibility for different applications circuits
and configurations. This board is not intended to be
used with high frequency components or high speed
amplifiers. However, it provides the user with many
combinations for various circuit types including active
filters, differential amplifiers, and external frequency
compensation circuits. A few examples of application
circuits are given in this application note.
C7
R7
R2
V_IN
R6
V_OUT
60
40
f_C
20
0
f_L
R7/R2 = 100
–20
f
10f
100f
1000f
RELATIVE FREQUENCY
Figure 1. Simple Low-Pass Filter
10000f
LOW-PASS FILTER
Figure 1 is a typical representation of a first-order low-
pass filter. This circuit has a 6 dB per octave roll-off
after a close-loop –3 dB point defined by f_C. Gain below
this frequency is defined as the magnitude of R7 to R2.
The circuit might be considered as an ac integrator for
frequencies well above f_C; however, the time domain
response is that of a single RC, rather than an integral.
f_C = 1/(2␲ ϫ R7 ϫ C7); –3 dB frequency
f_L = 1/(2␲ ϫ R2 ϫ C7); unity gain frequency
Acl = –(R7/R2); close loop gain
R6 should be chosen equal to the parallel combination
between R7 and R2 in order to minimize errors due to
bias currents.
R7
R2
V_IN1
R4
V_IN2
R6
V_OUT
Figure 2. Difference Amplifier
DIFFERENCE AMPLIFIER AND PERFORMANCE
OPTIMIZATION
Figure 2 shows an op amp configured as a difference
amplifier. The difference amplifier is the complement
of the summing amplifier, and allows the subtraction
of two voltages or the cancellation of a signal common
to both inputs. The circuit shown in Figure 2 is useful
as a computational amplifier in making a differential
to single-ended conversion or in rejecting a common-
mode signal. The output voltage V_OUT is comprised of
two separate components:
1. A component V_OUT1 due to V_IN1 acting alone (V_IN2
short-circuited to ground.)
2. A component V_OUT2 due to V_IN2 acting alone (V_IN1
short-circuited to ground.)
REV. A