ADA4522-4ARZ-R7 datasheet(33/48 Pages) AD

33 / 48 page

Data Sheet

ADA4522-1/ADA4522-

2/ADA4522-4

analog.com

Rev I 33 of 48

comparison to standard low noise amplifiers that are susceptible to 1/f noise. Figure 63 shows the 0.1 Hz to 10 Hz

noise to be only 117 nV p-p of noise.

Source Resistance

The ADA4522-1/ADA4522-2/ADA4522-4 are some of the lowest noise high voltage zero drift amplifiers with 5.8 nV/√Hz

of voltage noise density at 1 kHz (AV = 100). Therefore, it is important to consider the input source resistance of choice

to maintain a total low noise. The total input referred broadband noise (eN total) from any amplifier is primarily a

function of three types of noise: input voltage noise, input current noise, and thermal (Johnson) noise from the

external resistors.

These uncorrelated noise sources can be summed up in a root sum squared (rss) manner by using the following

equation:

eN total = (eN 2 + 4 kTRS + (IN × RS) 2 ) 1/2

(3)

where:

eNis the input voltage noise density of the amplifier (V/√Hz).

k is the Boltzmann constant (1.38 × 10−23 J/K).

T is the temperature in Kelvin (K).

RS is the total input source resistance (Ω).

IN is the input current noise density of the amplifier (A/√Hz).

The total equivalent rms noise over a specific bandwidth is expressed as:

�� = ��√��

(4)

where BW is the bandwidth in hertz.

This analysis is valid for broadband noise calculation up to a decade before the switching frequency. If the bandwidth

of concern includes the switching frequency, more complicated calculations must be made to include the effect of

the increase in noise at the switching frequency.

With a low source resistance of RS < 1 kΩ, the voltage noise of the amplifier dominates. As the source resistance

increases, the thermal noise of RS dominates. As the source resistance further increases, where RS > 50 kΩ, the current

noise becomes the main contributor of the total input noise.

Residual Ripple

As shown in Figure 60, Figure 62, and Figure 64, the ADA4522-1/ADA4522-2/ADA4522-4 have a flat noise spectrum

density at lower frequencies and exhibits spectrum density bumps and peaks at higher frequencies.

The largest noise bump is centered at 6 MHz; this bump is due to the decrease in the input gain at higher

frequencies.This decrease is a typical phenomenon and can also be seen in other amplifiers. In addition to the noise

bump, a sharp peak due to the chopping networks is seen at 4.8 MHz. However, this magnitude is significantly

reduced by the offset and ripple correction loop. Its magnitude may be different with different amplifier units or with

different circuitries around the amplifier. This peak can potentially be hidden by the noise bump and, therefore, may

not be detected.

ADA4522-4ARZ-R7 Datasheet(PDF) 33 Page - Analog Devices

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