ADA4522-4ARUZ-R7 datasheet(34/48 Pages) AD

34 / 48 page

Data Sheet

ADA4522-1/ADA4522-

2/ADA4522-4

analog.com

Rev I 34 of 48

The offset and ripple correction loop, designed to reduce the 4.8 MHz switching artifact, also creates a noise bump

centered at 800 kHz and a noise peak on top of this noise bump. Although the magnitude of the bump is mostly

constant, the magnitude of the 800 kHz peak is different from unit to unit. Some units may not exhibit the 800 kHz

noise peak; however, for other units, peaks occur at multiple integrals of 800 kHz, such as 1.6 MHz or 2.4 MHz.

These noise peaks, albeit small in magnitude, can be significant when the amplifier has a closed-loop frequency that

is higher than the chopping frequency. To suppress the noise spike to a desired level, either configure the amplifier

in a high gain configuration or apply a post filter at the output of the amplifier.

Figure 76

shows the voltage noise density of the ADA4522-1/ADA4522-2/ADA4522-4 in various gain configurations.

Note that the higher the gain, the lower the available bandwidth is. The earlier bandwidth roll-off effectively filters

out the higher noise spectrum.

Figure 76.Voltage Noise Density with Various Gains

Figure 77

shows the voltage noise density of the ADA4522-1/ADA4522-2/ADA4522-4 without and with post filters at

different frequencies. The post filter serves to roll off the bandwidth before the switching frequency. In this example,

the noise peak at 800 kHz is about 38 nV/√Hz. With a post filter at 80 kHz, the noise peak is reduced to 4.1 nV/√Hz.

With a post filter at 8 kHz, the noise peak is lower than the noise floor and cannot be detected.

Figure 77.Voltage Noise Density with Post Filters

100

10k

100k

10M

100M

FREQUENCY (Hz)

VSY = ±15V

AV = 1

AV = 10

AV = 100

100

10k

100k

10M

100M

FREQUENCY (Hz)

AV = 1

AV = 1 (POST FILTER AT 80kHz)

AV = 1 (POST FILTER AT 8kHz)

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