Regular paper Low-voltage subthreshold CMOS current mode circuits: Design and applications Mohammed A. Eldeeb a,⇑ , Yehya H. Ghallab b,c , Yehea Ismail c , Hassan Elghitani a a Department of Electronics and Communication, Misr International University, Cairo, Egypt b Biomedical Engineering Department, Helwan University, Cairo, Egypt c Center of Nanoelectronics and Devices at Zewail City of Science and Technology/AUC, Cairo, Egypt article info Article history: Received 30 April 2017 Accepted 29 August 2017 Keywords: CMOS circuits Current-mode circuits G m /I D design methodology Low voltage Self-cascode Subthreshold abstract The world has migrated to portable applications ranging from smart phones to Lab on a Chip applications. However they come with a new set of challenges for analog IC designers. Low voltage operation, small area and low noise are the critical design criteria for portable devices. This paper presents a g m /I D based design methodology for low voltage current mode circuits using standard CMOS technology. A second generation current conveyor (CCII) and a current feedback operational amplifier (CFA) are designed using the discussed design procedure. Both circuits operate from a single 0.4 V supply. The CCII is used to implement an instrumentation amplifier. Multiple applications are implemented using the CFA. Post lay- out simulation using TSMC 90 nm and UMC 130 nm technology show that the presented design proce- dure is an attractive solution for low voltage CMOS current mode circuits. Ó 2017 Elsevier GmbH. All rights reserved. 1. Introduction We live in a world that’s constantly on the move. To accommo- date, our applications have all become smaller and faster. Starting from laptops and wearable heart monitors to Lab on a Chip appli- cations where multiple labs are integrated onto a single chip a few cm 2 in area. Fitness trackers for example are rapidly gaining popu- larity [1]. In sports they are used to enhance the performance of athletes and help them to reduce the risk of injury during training [2]. In medicine, the uses range from glucose level measuring to heart monitoring and automated drug delivery [3]. Physiological signals reside below a few kHz and at most few mV in amplitude [4] which makes them susceptible to flicker noise and external noise sources. These devices require low noise low power minia- ture analog front-end circuitry. In this paper we present a design procedure for current mode circuits using standard CMOS technol- ogy suitable for low voltage applications. There are various methods for low voltage design [5–7]. The g m / I D design methodology has proven to be energy and area efficient when designing operational amplifiers [8,9]. In recent years, inter- est in current mode circuits has risen primarily due to their ability to operate from a low voltage source [10–16]. Previously published state of the art low voltage second generation current conveyor (CCII) use either bulk driven techniques [17] that occupy large areas due to the required isolation of MOSFETs with different bulk poten- tial. The other technique uses Floating Gate MOSFETs [18] which require extra steps during fabrication. There are few implementa- tions that use Carbon Nanotube (CNT) technology [19]. However, these are not easily integrated into VLSI systems that use standard CMOS technology. In this paper and based on the g m /I D methodol- ogy, the most commonly used current mode device, [i.e., the Second Generation Current Conveyor (CCII)] is designed, simulated and pre- sented. Then, the CCII is then used to implement a Current Feedback Operational Amplifier (CFA) [20]. A couple of applications using the CCII and CFA are simulated and presented to showcase the feasibil- ity of the design procedure. The remainder of the paper is organized as follows; the behavior of the MOSFET in subthreshold region is discussed in part II. Part III discusses the CCII circuit design proce- dure, simulation results and applications based on CCII. The CFA cir- cuit design, simulation results and applications based on CFA are presented and discussed in Part IV. Part V concludes the paper. 2. Behavior of MOSFET in subthreshold region Operating in the subthreshold region with newer technology is feasible as it’s easy to achieve a drain current of few mA which corresponds to a few kHz of bandwidth sufficient for multiple applications like biomedical applications [e.g.: ECG, EEG and EMG http://dx.doi.org/10.1016/j.aeue.2017.08.049 1434-8411/Ó 2017 Elsevier GmbH. All rights reserved. ⇑ Corresponding author. E-mail addresses: mohammed.eldeeb@aucegypt.edu (M.A. Eldeeb), yghallab@ zewailcity.edu.eg (Y.H. Ghallab), yismail@zewailcity.edu.eg (Y. Ismail), hassan. elghitani@miuegypt.edu.eg (H. Elghitani). Int. J. Electron. Commun. (AEÜ) 82 (2017) 251–264 Contents lists available at ScienceDirect International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue