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.

+VSY

–VSY

IN

VO

fO =

R1 = R2 = 2R3

C1 = C2 =

R1

804kΩ

R2

804kΩ

R3

402kΩ

C3

6.6nF

C2

3.3nF

C3

2

C1

3.3nF

ADA4062-x

1

2π R1 C1

Figure 59. Notch Filter Circuit

FREQUENCY (Hz)

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 ≤

VCM ≤ +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

+15V

+15V

–15V

100kΩ

0.1Ω

100kΩ

500kΩ

500kΩ

VO

RL

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

10.1kΩ

R4

1MΩ

+15V

1/2

–15V

V1

R2

1MΩ

+15V

–15V

V2

R1

10.1kΩ

ADA4062-2

ADA4062-2

VO

VO = 100(V2 – V1)

TYPICAL: 0.5mV < │V2 – V1│< 135mV

TYPICAL: –13.8V < VO < +13.5V

USE MATCHED RESISTORS

1/2

Figure 62. Micropower Instrumentation Amplifier