One of the most important building blocks in modern IC design is the operational amplifier. For the portable electrocardiogram (ECG), the operational amplifier is employed to sense and amplify the electrical signal of heartbeat of human body. For the battery powered portable ECG system, low supply voltage environments are required to reduce power consumption and the result is a reduced input common mode range (ICMR) of the op-amp. To overcome the reduced ICMR problem, complementary differential pairs operated in parallel are commonly used to achieve a rail-to-rail input common mode range. However, this complementary differential input pair structure can have a substantial transconductance (gm) variation problem and a dead zone problem in a low supply voltage environment and an extremely low supply voltage environment respectively. In the past years, a number of techniques have been proposed to overcome those problems for low- and extremely low-supply voltage environments. This dissertation is focused on an op-amp applicable to a portable ECG system and in total five novel rail-to-rail constant gm op-amps usful for circuits such as a portable ECG are proposed. Three of those op-amps work in the low supply voltage environment and two op-amps are proposed for the extremely low supply voltage environment. Cadence SPECTRE simulation and TSMC 0.25-microm CMOS technology are used to simulate and lay out these works.
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