AD712AH Analog Devices, AD712AH Datasheet - Page 13

• Manufacturer Part Number: AD712AH
• Description: Dual Precision/ Low Cost/ High Speed/ BiFET Op Amp
• Manufacturer: Analog Devices

REV. B
SECOND ORDER LOW PASS FILTER
Figure 38 depicts the AD712 configured as a second order
Butterworth low pass filter. With the values as shown, the corner
frequency will be 20 kHz; however, the wide bandwidth of the
AD712 permits a corner frequency as high as several hundred
kilohertz. Equations for component selection are shown below.
An important property of filters is their out-of-band rejection.
The simple 20 kHz low pass filter shown in Figure 38, might be
used to condition a signal contaminated with clock pulses or
sampling glitches which have considerable energy content at
high frequencies.
The low output impedance and high bandwidth of the AD712
minimize high frequency feedthrough as shown in Figure 39.
The upper trace is that of another low-cost BiFET op amp
showing 17 dB more feedthrough at 5 MHz.
C1 (in farads )
R1 = R2 = user selected (typical values: 10 k – 100 k )
Figure 38. Second Order Low Pass Filter
V
IN
20k
R1
280pF
20k
(2 )( f
R2
C2
1.414
560pF
cutoff
C1
AD712
)(R1)
+15V
–15V
1/2
0.1 F
0.1 F
C2
(2 )( f
0.707
V
OUT
cutoff
)(R1)
–13–
CENTER 5 000 000.0 Hz
RBW 30 kHz
REF 20.0 dBm
10 dB/DIV
TYPICAL BIFET
VBW 30 kHz
RANGE 15.0 dBm
Figure 39.
AD712
SPAN 10 000 000.0 Hz
OFFSET .0 Hz
ST .8 SEC
0 dB
AD712