Hybrid Frequency Compensation to Improve Unity-Gain Bandwidth of Low-Voltage Low-Power CMOS Operational Amplifiers

In this paper a new hybrid frequency compensation (HFC) technique consists of indirect compensation and compensation using unbalanced differential pairs for low-voltage low-power CMOS operational amplifiers (op amp) is proposed. This technique significantly improves frequency response of the op amp and avoids instability when a large capacitive load at the output of the op amp must be handled. Also, Dynamic threshold voltage MOSFET (DTMOS) and sub-threshold region are utilized in the design to effectively use the low supply voltage and reduce power consumption. To evaluate the proposed technique, the two stage operational amplifier is designed and simulated in a TSMC 0.18 μm CMOS process technology. The op amp operate at 0.6 V power supply with 138.3 nW power consumption. The proposed HFC technique uses a total compensation capacitance of 3.5 pF and is robust in stability under the variation of the load capacitance between 0 pF and 100 pF. When driving a 15 pF load, the proposed HFC amplifier reduces the total capacitor size 35% and improves the unity-gain bandwidth 481% compared to the conventional Miller compensation.