AD823 Analog Devices, AD823 Datasheet - Page 17

• Manufacturer Part Number: AD823
• Description: Dual, 16 MHz, Rail-to-Rail FET Input Amplifier
• Manufacturer: Analog Devices

Specifications of AD823

• -3db Bandwidth: 16MHz
• Slew Rate: 25V/µs
• Vos: 700µV
• Ib: 5pA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 16nV/rtHz
• Vcc-vee: 3V to 36V
• Isy Per Amplifier: 4.2mA
• Packages: DIP,SOIC

Data Sheet
Second-Order Low-Pass Filter
Figure 43 depicts the AD823 configured as a second-order
Butterworth low-pass filter. With the values as shown, the
corner frequency equals 200 kHz. Component selection is
shown in the following equations:
R1 = R2 = User Selected (Typical Values: 10 kΩ to 100 kΩ)
A plot of the filter is shown in Figure 44; better than 50 dB of
high frequency rejection is provided.
V
C1
C2
IN
–10
–20
–30
–40
–50
–60


0
farads
1k
2π
20kΩ
R1
f
. 0
cutoff

Figure 43. Second-Order Low-Pass Filter
Figure 44. Frequency Response of Filter
707

20kΩ
28pF
10k
R2
2π

C1
R1
f
56pF
1
cutoff
C2
.
414
FREQUENCY (Hz)

100k
AD823
R1
1/2
+5V
–5V
0.1µF
0.1µF
C4
C3
V
1M
DB
– V
OUT
10M
50pF
V
100M
OUT
Rev. E | Page 17 of 20
Single-Supply Half-Wave and Full-Wave Rectifiers
An AD823 configured as a unity-gain follower and operated
with a single supply can be used as a simple half-wave rectifier.
The AD823 inputs maintain picoamp level input currents even
when driven well below the minus supply. The rectifier puts
that behavior to good use, maintaining an input impedance of
over 10
supply to 20 V below the negative supply.
The full-wave and half-wave rectifier shown in Figure 45
operates as follows: when V
strapped through the unity-gain follower A1 and the loop of
Amplifier A2. This forces the inputs of A2 to be equal, thus no
current flows through R1 or R2, and the circuit output tracks
the input. When V
to ground. The noninverting input of Amplifier A2 sees the
ground level output of A1; therefore, A2 operates as a unity-
gain inverter. The output at Node C is then a full-wave rectified
version of the input. Node B is a buffered half-wave rectified
version of the input. Input voltage supply to ±18 V can be
rectified, depending on the voltage supply used.
V
A
IN
A
B
C
11
Figure 46. Single-Supply Half-Wave and Full-Wave Rectifier
10
0%
100
90
Ω for input voltages from within 1 V of the positive
2
3
2V
Figure 45. Full-Wave and Half-Wave Rectifier
8
A1
+V
S
4
2V
AD823
0.01µF
100kΩ
IN
R1
1
1/2
is below ground, the output of A1 is forced
IN
is above ground, R1 is boot-
5
6
A2
A2
AD823
100kΩ
1/2
R2
7
200µs
FULL-WAVE
RECTIFIED OUTPUT
HALF-WAVE
RECTIFIED OUTPUT
C
B
AD823