Auto Zero Amplifier vs. Chopper Stabilized Amplifier

This article highlights the differences between auto zero amplifiers and chopper stabilized amplifiers.

Introduction:

Zero-drift amplifiers dynamically correct offset voltage and readjust their noise density. Two main architectures are used to design these amplifiers: auto zero amplifiers and chopper stabilized amplifiers.

Auto Zero Amplifier

Image alt: Auto zero amplifier characteristic

• It uses sampling to correct the offset.
• This sampling causes noise to fold back into the baseband region, resulting in more in-band noise.
• It requires more current to suppress the noise, leading to higher power dissipation.
• The figure above illustrates the characteristic of an auto zero amplifier compared to a standard operational amplifier. As shown, the auto zero amplifier exhibits more in-band noise than a standard op-amp.

Chopper Stabilized Amplifier

Image alt: Chopper stabilized amplifier characteristic

• It utilizes modulation and demodulation, making it suitable for low-frequency applications.
• It produces a large magnitude of energy at the chopping frequency and its harmonics.
• It has low-frequency noise consistent with its flat band noise.
• Output filtering is required.
• The figure depicts the characteristic of a chopper stabilized amplifier, a standard op-amp, and a combined version.
• The combined technique reduces energy at the chopping frequency and keeps noise very low at lower frequencies. Moreover, this combined version offers a wider operating bandwidth.

Auto Zero Amplifier vs. Chopper Stabilized Amplifier

The following table summarizes the differences between auto zero and chopper stabilized amplifiers. The information is based on research by Analog Devices, Inc. The ADI part number AD8628 is a zero-drift amplifier that combines both auto zeroing and chopping techniques.

The AD8628 from Analog Devices Inc. combines the functionalities of both auto zero and chopper stabilized amplifiers.