Analogue circuit design methodology using self‐cascode structures

Abstract

A new analogue circuit design methodology using independently optimised self-cascode (SC) structures is proposed. Based on the concept of the dual-workfunction-gate structures, which are equivalent to SC structures, transconductance and output resistance optimised SC MOSFETs were used in the differential input and output stages, respectively. An operational amplifier (opamp) with the proposed design methodology using standard 0.18 µm CMOS technology was designed to provide better performance. The measured DC gain of the fabricated opamp with independently-optimised SC MOSFETs was approximately 12 dB higher than that of the conventional opamp.

Ultra-Low Voltage Analog IC Design: Challenges, Methods and Examples

“…5) is a two-transistor structure, which can be treated as a single transistor. Gates of both transistors are driven by a common input signal [16]. The self-cascode technique offers higher output impedance and reduces the effect of Miller capacitance on the transistor gates.…”

“…The basic principle of this technique is in different threshold voltages of the transistors (i.e. V TH1 V TH2 ), which is not available in a standard low-cost CMOS process [16].…”

Design techniques for low-voltage analog integrated circuits

“…The output resistance r out of this topology is approximately proportional to (W/L) 2 /(W/L) 1 ratio, and the saturation voltage V DS(sat) = V GS −V T H is roughly comparable with the conventional MOS transistor. The basic principle of this technique is in different threshold voltages (V T H2 = V T H1 ), which is not feasible in the standard low-cost CMOS process [4]. …”

High DC gain self‐cascode structure of OTA design with bandwidth enhancement

“…However, both of the SC structures in [2,3] require additional or complicated fabrication processing steps which would increase the cost. Moreover, the SC structure in [4] achieves high output resistance and transconductance through additional bias voltage which eliminates the drawbacks in [1][2][3], but the DC gain of [1][2][3][4] is still not enough especially in deep sub-micron process and the RC compensation technology in [2][3][4] restrict the unity-gain bandwidth of the OTA which perform an unsatisfactory FOM.…”

“…This Letter proposes a better SC structure of OTA with the similar concept of [4] which produces high output resistance and transconductance. Furthermore, the proposed structure exhibits a compensation methodology to obtain better unity-gain bandwidth compared with [2][3][4]. As a result, the advantages of the proposed OTA bring an excellent FOM.…”