ADA4062-2/ADA4062-4
Rev. B | Page 15 of 20
APPLICATIONS INFORMATION
NOTCH FILTER
A notch filter rejects a specific interfering frequency and can be
implemented using a single op amp. Figure 59 shows a 60 Hz
notch filter that uses the twin-T network with the ADA4062-x
configured as a voltage follower. The ADA4062-x works as a buffer
that provides high input resistance and low output impedance.
The low bias current (2 pA typical) and high input resistance
(10 TΩ typical) of the ADA4062-x enable large resistors and small
capacitors to be used.
Alternatively, different combinations of resistor and capacitor
values can be used to achieve the desired notch frequency.
However, the major drawback to this circuit topology is the
need to ensure that all the resistors and capacitors be closely
matched. If they are not closely matched, the notch frequency
offset and drift cause the circuit to attenuate at a frequency
other than the ideal notch frequency.
Therefore, to achieve the desired performance, 1% or better
component tolerances are usually required. In addition, a notch
filter requires an op amp with a bandwidth of at least 100× to
200× the center frequency. Hence, using the ADA4062-x with
a bandwidth of 1.4 MHz is excellent for a 60 Hz notch filter.
Figure 60 shows the frequency response of the notch filter. At
60 Hz, the notch filter has about 50 dB attenuation of signal.
+V
SY
–V
SY
IN
V
O
f
O
=
R1 = R2 = 2R3
C1 = C2 =
07670-060
R1
804k
R2
804k
R3
402k
C3
6.6nF
C2
3.3nF
C3
2
C1
3.3nF
ADA4062-x
1
2 R
1
C
1
Figure 59. Notch Filter Circuit
07670-057
FREQUENCY (Hz)
GAIN (dB)
20
10
0
–10
–30
–20
–40
–50
–60
–70
–80
10 100 1k
Figure 60. Frequency Response of the Notch Filter
HIGH-SIDE SIGNAL CONDITIONING
Many applications require the sensing of signals near the positive
rail. The ADA4062-x can be used in high-side current sensing
applications. Figure 61 shows a high-side signal conditioning
circuit using the ADA4062-x. The ADA4062-x has an input
common-mode range that includes the positive supply (−11.5 V ≤
V
CM
≤ +15 V). In the circuit, the voltage drop across a low value
resistor, such as the 0.1 Ω shown in Figure 61, is amplified by a
factor of 5 using the ADA4062-x.
ADA4062-x
+15
+15V
–15V
100k
0.1
100k
500k
500k
V
O
R
L
07670-058
Figure 61. High-Side Signal Conditioning
MICROPOWER INSTRUMENTATION AMPLIFIER
The ADA4062-2 is a dual amplifier and is perfectly suited for
applications that require lower supply currents. For supply
voltages of ±15 V, the supply current per amplifier is 165 μA
typical. The ADA4062-2 also offers a typical low offset voltage
drift of 5 μV/°C and a very low bias current of 2 pA, which
make it well suited for instrumentation amplifiers.
Figure 62 shows the classic 2-op-amp instrumentation amplifier
with four resistors using the ADA4062-2. The key to high CMRR
for this instrumentation amplifier are resistors that are well
matched to both the resistive ratio and relative drift. For true
difference amplification, matching of the resistor ratio is very
important, where R3/R4 = R1/R2. Assuming perfectly matched
resistors, the gain of the circuit is 1 + R2/R1, which is approximately
100. Tighter matching of two op amps in one package, as is the
case with the ADA4062-2, offers a significant boost in performance
over the classical 3-op-amp configuration. Overall, the circuit only
requires about 330 μA of supply current.
R3
10.1k
R4
1M
+15V
1/2
–15V
V1
R2
1M
+15V
–15V
V2
R1
10.1k
ADA4062-2
ADA4062-2
V
O
V
O
= 100(V2 – V1)
TYPICAL: 0.5mV < V2 – V1< 135mV
TYPICAL: –13.8V < V
O
< +13.5V
USE MATCHED RESISTORS
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1/2
Figure 62. Micropower Instrumentation Amplifier
