| Version | Summary | Created by | Modification | Content Size | Created at | Operation |
|---|---|---|---|---|---|---|
| 1 | Sirius Huang | -- | 1826 | 2022-11-07 01:41:41 |
CMOS amplifiers are ubiquitous analog circuits which are used in computers, audio systems, smart phones, cameras, telecommunication systems, biomedical circuits and many other systems, and their performance has great impact on the overall specifications of the systems. They take their name from the use of MOSFET (Metal Oxide Semiconductor Field Effect Transistor) as opposite to Bipolar Junction Transistors (BJT). MOSFETS are simpler to fabricate and therefore less expensive than BJT amplifiers, still providing a sufficiently high transconductance to allow the design of very high performance circuits. In high performance CMOS amplifier circuits, transistors are not only used to amplify the signal but are also used as active loads to achieve higher gain and output swing in comparison with resistive loads. CMOS technology had been primarily introduced to design digital circuits. In the last decades, in order to improve speed, power consumption, required area and other aspects of digital integrated circuits (ICs), the feature size of MOSFET transistors has shrunk (minimum channel length of transistors reduces in newer CMOS technologies). This phenomenon predicted by Gordon Moore in 1975, which is called Moore’s law, and states that in about each 2 years, the number of transistors doubles for the same silicon area of ICs. Progress in memory circuits design is an interesting example to see how process advancement have affected the required size and their performance in the last decades. In 1956, a 5MB Hard Disk Drive (HDD) weighted over a tone, while these days having 50000 times more capacity with a weight of several tens of grams is very common. While digital ICs have enormously benefited from the feature size shrinking, analog CMOS amplifiers have not gained corresponding advantages due to the intrinsic limitations imposed by an analog design, like the intrinsic gain reduction of short channel transistors which affects the overall gain of amplifier. Novel techniques to achieve higher gain also create new problems, like stability of amplifier for closed-loop applications. In the following, we will address both aspects and summarize few different methods to overcome these problems.