A rail-to-rail constant-gm CCII for Instrumentation Amplifier applications

doi:10.1016/j.aeue.2018.04.029

AEU - International Journal of Electronics and Communications

Volume 91, July 2018, Pages 103-109

https://doi.org/10.1016/j.aeue.2018.04.029 Get rights and content

Abstract

We here present a current mode Instrumentation Amplifier (IA) based on second generation current conveyor (CCII) with complete input/output dynamic range (rail-to-rail) and constant-g_m characteristics. The IA operates at 1.5 V supply with 177 μW power consumption, high-loop gain (115 dB) and high CMRR (105 dB). The proposed IA has been implemented by using a standard AMS 0.35-μm CMOS technology. SPICE simulations are also reported.

Introduction

The continuous and ever-increasing demand of portable electronic devices with prolonged autonomy such as, for instance, in electromedical, wireless sensor network and Internet of Things applications, requires the development of challenging circuit solutions and design techniques aimed at further minimizing power consumption maintaining good general performances [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]. In this perspective, Instrumentation Amplifiers (IAs) are widely used in data acquisition systems and signal processing applications. Particular kinds of IAs, based on the current-mode approach, are the Current-Mode Instrumentation Amplifiers (CMIAs) [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]. The most important performance parameter of an IA is the Common Mode Rejection Ratio (CMRR) which indicates how well it is possible to measure the desired differential signal under the presence of large unwanted common mode ones. Generally, the CMRR of an IA not only depends on the matching between the used active elements but also on the external resistor tolerances. Moreover, the supply voltage also greatly affects IA performances; in particular, decreasing the supply voltage reduces the maximum number of stacked gate-source voltages and saturation voltages allowed between the supply rails. Signal swing may be also severely impaired and, to mitigate this drawback, complete dynamic (rail-to-rail) topologies must be selected. Specifically, as far as input differential stages is concerned, rail-to-rail solutions are implemented through two complementary source-coupled pairs connected in parallel. This requires also the control of the total transconductance (g_m), which has to be kept constant over the whole input common-mode voltage range, so that power-efficient frequency compensation techniques providing a constant Gain-Bandwidth (GBW) can be employed [25], [26], [27], [28], [29], [30], [31], [32].

All these considerations can be directly applied to the implementation of a low-voltage current mode IA. This work presents the design of a constant-g_m rail-to-rail low voltage CCII-based IA operating at a 1.5 V power supply showing a 177 μW power consumption and a CMRR of about 105 dB.

Section snippets

The proposed constant-G_m rail-to-rail CCII

In order to develop a constant-g_m CCII, the simplified block scheme in Fig. 1 is adopted. It consists of three stages. The first one (input stage) is an Operational Transconductance Amplifier (OTA), made up of two complementary input pairs in parallel providing rail-to-rail operation (plus a control circuitry ensuring a constant-g_m operation for the input stage, not shown). The output currents of the two complementary pairs are added at their single-ended output. The second stage (INV X) is an

The proposed CCII based rail-to-rail IA: simulation results

The basic block scheme of the proposed current mode IA is shown in Fig. 4 [23], [24]. It is based on two CCIIs as active building blocks which transfer Y terminal voltage to X one and converts it to a current using a resistor. The current produced at X terminal is copied to output (Z terminal). The ideal input-output relationship is given in Eq. (10). $V_{out} = (V_{in +} - V_{in -}) * \frac{R_{2}}{R_{1}}$

Simulation results

The complete circuit was designed in a standard CMOS technology (0.35-µm by AMS) designing two identical CCII. Transistor dimensions of the single CCII are shown in Table 1. For the single CCII, at a 1.5 V supply voltage, DC power dissipation is 88.5 µW. Always concerning the standalone CCII, Fig. 5 shows the transconductance of both the n- and p-channel CCII differential pairs, as well as the total transconductance g_mT, given by the sum of the two g_m’s, that can be considered constant with the

Conclusions

We have proposed a current mode Instrumentation Amplifier (IA) based on second generation current conveyor (CCII) with rail-to-rail and constant-g_m characteristics. Simulation results have shown the validity of the proposed architecture for integrated circuits for low-voltage portable applications.

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As a result, current conveyors are widely used to realize analog signal processing circuits; see, for example [2–12]. The circuits in [7–12] use conventional CCII as active element. The conventional CCII [1] has three terminals (y-, x-, z-terminals) which usually possesses high impedance at y- and z-terminals (infinity for ideal) and low impedance at x-terminal (zero for ideal).
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Regular paperA rail-to-rail constant-gm CCII for Instrumentation Amplifier applications

Abstract

Introduction

Section snippets

The proposed constant-Gm rail-to-rail CCII

The proposed CCII based rail-to-rail IA: simulation results

Simulation results

Conclusions

Low voltage, low power VLSI subsystems

Low-power low-voltage VLSI operational amplifier cells

IEEE Trans Circuits Syst I: Fundam Theory Appl

A survey of non-conventional techniques for low-voltage low-power analog circuit design

Radioeng J

The gm/ID methodology, a sizing tool for low-voltage analog CMOS circuits

A programmable 1.5 V CMOS class-AB operational amplifier with hybrid nested Miller compensation for 120 dB gain and 6 MHz UGF

IEEE J Solid-State Circuits

Analog circuit design low voltage low power; short range wireless front-ends; power management and DC-DC

A rail-to-rail constant-gm low-voltage CMOS operational transconductance amplifier

IEEE J. Solid-State Circuits

Inverter-based low-voltage CCII design and its filter application

Radioengineering

Low-voltage low-power CMOS current conveyors

Regular paper
A rail-to-rail constant-g_m CCII for Instrumentation Amplifier applications

The proposed constant-G_m rail-to-rail CCII

A programmable 1.5 V CMOS class-AB operational amplifier with hybrid nested Miller compensation for 120 dB gain and 6 MHz UGF