The power consumption of electronic devices has been a great interest for decades. Lower power means smaller battery, less energy dissipation, less heat generated and many other benefits. But lower power leads to higher noise level which limits the performance of any electronic devices, for example amplifiers.
There are many noise sources that limit the performance of an amplifier. Flicker and thermal noise are two of the most conventional ones. In order to minimize the thermal noise, usually, the input transistors of amplifiers are biased in weak inversion to maximize gm/ID. As the required noise floor decreases, higher power is required. In order to increase the input transconductance without increasing current, inverter-based or current reuse structure is proposed. Furthermore, stacking and orthogonal inverter-based amplifiers have been suggested in many applications to increase the gm more than before. In addition, in order to minimize the flicker noise, usually the size of the transistors are larger than normal values. But it will be at the cost of larger area consumption.
Chopping and Auto-zeroing techniques are two conventional techniques to minimize the noise in system level. Auto-zeroing uses sampling to correct offset, whereas chopping uses modulation and demodulation. Sampling causes noise to fold back into the baseband. Chopping technique is one of the best approaches due to of their good trade-off between noise and power. In addition, it improves the CMRR of the designed circuit. Chopper amplifiers usually use a high switching frequency to minimize the flicker noise of a circuit. Consequently, their input impedance is lower than other techniques.
For more information, you can find the documents below as a reference.
- Master Thesis: https://ntnuopen.ntnu.no/ntnu-xmlui/bitstream/handle/11250/2788504/no.ntnu%3Ainspera%3A77038608%3A21512514.pdf?sequence=1
- Article 1: https://ieeexplore.ieee.org/document/7828037
- Article 2: https://ieeexplore.ieee.org/abstract/document/9498105
- Article 3: https://ieeexplore.ieee.org/abstract/document/9497971