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Difference between Auto zero amplifier and chopper stabilized amplifier

This page Auto zero amplifier vs chopper stabilized amplifier and mentions difference between Auto zero amplifier and chopper stabilized amplifier.

Introduction: Zero drift amplifier corrects offset voltage dynamically and re-adjusts its noise density. There are two architectures used to design zero drift amplifiers viz. auto zero amplifier and chopper stabilized amplifier.

Auto zero amplifier ?

Auto zero amplifier characteristic

• It uses sampling to correct the offset.
• It causes noise to fold back in baseband region. Hence it has more in-band noise.
• It requires more current to suppress the noise and hence it dissipates more power.
• The figure depicts the characteristic of auto zero amplifier and standard op amp. As shown, auto zero amplifier has more in band noise compare to standard operational amplifier.

Chopper stabilized amplifier ?

Chopper stabilized amplifier characteristic

• It uses modulation and demodulation. It is used for low frequency applications.
• It produces large magnitude of energy at chopping frequency and at its harmonics.
• It has low frequency noise consistent with its flat band noise.
• It requires output filtering.
• The figure depicts the characteristic of chopper stabilized amplifier, standard op amp and combined version.
• The combined technique will reduce energy at chopping frequency and keeps noise very low at lower frequencies. Moreover combined version offers wide operating bandwidth.

Auto zero amplifier vs chopper stabilized amplifier

Following table mentions difference between Auto zero amplifier and Chopper stabilized amplifier. The information provided in the table, is derived from research by Analog Devices, Inc. The ADI part number AD8628 is a zero drift amplifier which uses combination of both auto zeroing and chopping techniques.

Auto zero Chopper stabilized
Very low offset Very low offset
Sample and hold Modulation / Demodulation
High low frequency noise due to aliasing Similar noise to flat band (No aliasing)
High power consumption Low power consumption
Low ripple High ripple
Wide Bandwidth Narrow Bandwidth
Little energy at auto zero frequency Lots of energy at chopping frequency

The part number AD8628 from Analog Devices Inc. combines functionalities of both auto zero amplifier and chopper stabilized amplifier.



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