ADA4528-1_17 Datasheet, PDF (20/28 Pages) Analog Devices – Precision, Ultralow Noise, RRIO, Zero-Drift Op Amp

ADA4528-1/ADA4528-2
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
The ADA4528-1/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 will be 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). A 1 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).
Data Sheet
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 parts do not
exhibit phase reversal.
3
2
V_IN
V_OUT
1
0
–1
V_SY = ±2.5V
–2 ^AV ^{= 1}
R_L = 10kΩ
–3
TIME (200µs/DIV)
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 parts 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.
Rev. D | Page 20 of 28