ADA4062-2

Rev. 0 | Page 14 of

20

APPLICATIONS INFORMATION

NOTCH FILTER

A notch filter rejects a specific interfering frequency and can

be implemented using a single op amp. Figure 53 shows a 60 Hz

notch filter that uses the twin T network with the ADA4062-2

configured as a voltage follower. The ADA4062-2 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 ADA4062-2 enable large resistors and

small capacitors to be used.

Alternatively, different combinations of resistors and capacitors

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 com-

ponent tolerances are usually required. In addition, a notch filter

requires an op amp with a bandwidth of at least 100 to 200 times

the center frequency. Hence, using the ADA4062-2 with a

bandwidth of 1.4 MHz is excellent for a 60 Hz notch filter.

Figure 54 shows the gain of the notch filter with respect to

frequency. At 60 Hz, the notch filter has about 50 dB atten-

uation of signal.

IN

R1 = R2 = 2R3

C1 = C2 =

R1

804kΩ

R2

804kΩ

R3

402kΩ

C3

6.6nF

C2

3.3nF

C3

2

C1

3.3nF

ADA4062-2

1/2

1

Figure 53. Notch Filter Circuit

FREQUENCY (Hz)

20

10

0

–10

–30

–20

–40

–50

–60

–70

–80

10

100

1k

Figure 54. Notch Filter: Gain vs. Frequency

HIGH-SIDE SIGNAL CONDITIONING

There are many applications that require the sensing of signals

near the positive rail. The ADA4062-2 can be used in high-side

current sensing applications. Figure 55 shows a high-side signal

conditioning circuit using the ADA4062-2. The ADA4062-2 has

an input common-mode range that includes the positive supply

a low value resistor, such as the 0.1 Ω shown in Figure 55, is

amplified by a factor of 5 using the ADA4062-2.

ADA4062-2

+15V

+15V

–15V

100kΩ

0.1Ω

100kΩ

500kΩ

500kΩ

1/2

Figure 55. 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 4 μV/°C

and a very low bias current of 2 pA, which makes it well suited for

instrumentation amplifiers.

Figure 56 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 approxi-

mately 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 3-op-amp configuration. Overall, the circuit

only requires about 330 μA of supply current.

R3

10.1kΩ

R4

1MΩ

+15V

–15V

V1

R2

1MΩ

+15V

–15V

V2

R1

10.1kΩ

ADA4062-2

ADA4062-2

TYPICAL: 0.5mV < │V2 – V1│< 135mV

USE MATCHED RESISTORS

1/2

1/2

Figure 56. Micropower Instrumentation Amplifier

PHASE REVERSAL

Phase reversal occurs in some amplifiers when the input common-

mode voltage range is exceeded. When the voltage driving the

input to these amplifiers exceeds the maximum input common-

mode voltage range, the output of the amplifiers changes polarity.