AD825 Analog Devices, AD825 Datasheet - Page 11

• Manufacturer Part Number: AD825
• Description: Low Cost, General-Purpose High Speed JFET Amplifier
• Manufacturer: Analog Devices

Specifications of AD825

• -3db Bandwidth: 46MHz
• Slew Rate: 140V/µs
• Vos: 1mV
• Ib: 10pA
• # Opamps Per Pkg: 1
• Input Noise (nv/rthz): 12nV/rtHz
• Vcc-vee: 10V to 36V
• Isy Per Amplifier: 7.2mA
• Packages: SOIC

SECOND-ORDER LOW-PASS FILTER
A second-order Butterworth low-pass filter can be implemented
using the AD825 as shown in Figure 33. The extremely low bias
currents of the AD825 allow the use of large resistor values and,
consequently, small capacitor values without concern for
developing large offset errors. Low current noise is another
factor in permitting the use of large resistors without having to
worry about the resultant voltage noise.
With the values shown, the corner frequency will be 1 MHz.
The equations for component selection are shown below. Note
that the noninverting input (and the inverting input) has an
input capacitance of 6 pF. As a result, the calculated value of C1
(12 pF) is reduced to 6 pF.
A plot of the filter frequency response is shown in Figure 34;
better than 40 dB of high frequency rejection is provided.
C1
C2
R1
=
(
=
farads
R2
2
π
=
f
. 1
CUTOFF
User
414
)
=
2
π
Selected
R1
f
. 0
CUTOFF
707
(
Typically
R1
10
k
Ω
to
100
k
Ω
)
Rev. F | Page 11 of 12
Figure 34. Frequency Response of Second-Order Butterworth Filter
–10
–20
–30
–40
–50
–60
–70
–80
V
IN
0
10k
Figure 33. Second-Order Butterworth Low-Pass Filter
9.31kΩ
R1
9.31kΩ
100k
R2
6pF
C2
24pF
C1
FREQUENCY (Hz)
AD825
1M
+5V
–5V
0.1µF
0.1µF
C3
C4
10M
V
OUT
100M
AD825