Data Sheet

ADA4528-1/ADA4528-2

Rev. F | Page 19 of 24

APPLICATIONS INFORMATION

The ADA4528-1/ADA4528-2 are precision, ultralow noise,

zero-drift operational amplifiers that feature a patented chop-

ping technique. This chopping technique offers ultralow input

offset voltage of 0.3 µV typical and input offset voltage drift of

0.002 µV/°C typical.

Offset voltage errors due to common-mode voltage swings

and power supply variations are also corrected by the chopping

technique, resulting in a typical CMRR figure of 158 dB and a

PSRR figure of 150 dB at 2.5 V supply voltage. The ADA4528-1/

ADA4528-2 have low broadband noise of 5.6 nV/√Hz (at f =

1 kHz, AV = +100, and VSY = 2.5 V) with no 1/f noise component.

These features are ideal for amplification of low level signals in

dc or subhertz high precision applications.

For more information about the chopper architecture of the

ADA4528-1/ADA4528-2, see the AN-1114 Application Note,

Lowest Noise Zero-Drift Amplifier Has 5.6 nV/√Hz Voltage

Noise Density.

INPUT PROTECTION

TheADA4528-1/ADA4528-2 have internal ESD protection diodes

that are connected between the inputs and each supply rail. These

diodes protect the input transistors in the event of electrostatic

discharge and are reverse biased during normal operation. This

protection scheme allows voltages as high as approximately 300 mV

beyond the rails to be applied at the input of either terminal

without causing permanent damage (see Table 4 in the Absolute

Maximum Ratings section).

When either input exceeds one of the supply rails by more than

300 mV, the ESD diodes become forward biased and large amounts

of current begin to flow through them. Without current limiting,

this excessive fault current causes permanent damage to the device.

If the inputs are subjected to overvoltage conditions, insert a

resistor in series with each input to limit the input current to 10 mA

maximum. However, consider the resistor thermal noise effect

on the entire circuit.

For example, at a 5 V supply voltage, the broadband voltage noise

of the ADA4528-1/ADA4528-2 is approximately 6 nV/√Hz (at

unity gain).A1 kΩ resistor has thermal noise of 4 nV/√Hz.Adding

a 1 kΩ resistor at the noninverting input pin increases the total

noise by 30% root sum square (rss).

RAIL-TO-RAIL INPUT AND OUTPUT

The ADA4528-1/ADA4528-2 feature rail-to-rail input and

output with a supply voltage from 2.2 V to 5.5 V. Figure 64

shows the input and output waveforms of the ADA4528-

1/ADA4528-2 configured as a unity-gain buffer with a supply

voltage of ±2.5 V and a resistive load of 10 kΩ. With an input

voltage of ±2.5 V, the ADA4528-1/ADA4528-2 allow the output

to swing very close to both rails. Additionally, the devices do

not exhibit phase reversal.

3

2

1

0

–1

–2

–3

TIME (200µs/DIV)

VIN

VOUT

VSY = ±2.5V

AV = 1

RL = 10kΩ

Figure 64. Rail-to-Rail Input and Output

NOISE CONSIDERATIONS

For more information about the noise characteristics of the

ADA4528-1/ADA4528-2, see the AN-1114 Application Note,

Lowest Noise Zero-Drift Amplifier Has 5.6 nV/√Hz Voltage Noise

Density.

1/f Noise

1/f noise, also known as pink noise or flicker noise, is inherent

in semiconductor devices and increases as frequency decreases.

At low frequency, 1/f noise is a major noise contributor and

causes a significant output voltage offset when amplified by the

noise gain of the circuit. However, the ADA4528-1/ADA4528-2

eliminate the 1/f noise internally, thus making these devices an

excellent choice for dc or subhertz high precision applications.

The 0.1 Hz to 10 Hz amplifier voltage noise is only 97 nV p-p

(AV = +100) at a supply voltage of 2.5 V.

The low frequency 1/f noise, which appears as a slow varying

offset to the ADA4528-1/ADA4528-2, is greatly reduced by

the chopping technique. This reduction in 1/f noise allows the

ADA4528-1/ADA4528-2 to have much lower noise at dc and

low frequency compared to standard low noise amplifiers that

are susceptible to 1/f noise. Figure 51 and Figure 54 show the

voltage noise density of the amplifier with no 1/f noise.