Bulk-driven Operational Transconductance Amplifier Research Articles

A 0.3V Rail-to-Rail Three-Stage OTA With High DC Gain and Improved Robustness to PVT Variations

This paper presents a novel 0.3V rail-to-rail body-driven three-stage operational transconductance amplifier (OTA). The proposed OTA architecture allows achieving high DC gain in spite of the bulk-driven input. This is due to the doubled body transconductance at the first and third stages, and to a high gain, gate-driven second stage. The bias current in each branch of the OTA is accurately set through gate-driven or bulk-driven current mirrors, thus guaranteeing an outstanding stability of main OTA performance parameters to PVT variations. In the first stage, the input signals drive the bulk terminals of both NMOS and PMOS transistors in a complementary fashion, allowing a rail-to-rail input common mode range (ICMR). The second stage is a gate-driven, complementary pseudo-differential stage with an high DC gain and a local CMFB. The third stage implements the differential-to-single-ended conversion through a body-driven complementary pseudo-differential pair and a gate-driven current mirror. Thanks to the adoption of two fully differential stages with common mode feedback (CMFB) loop, the common-mode rejection ratio (CMRR) in typical conditions is greatly improved with respect to other ultra-low-voltage (ULV) bulk-driven OTAs. The OTA has been fabricated in a commercial 130nm CMOS process from STMicroelectronics. Its area is about 0.002 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mm</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and power consumption is less than 35nW at the supply-voltage of 0.3V. With a load capacitance of 35pF, the OTA exhibits a DC gain and a unity-gain frequency of about 85dB and 10kHz, respectively.

A 0.25-V Three-stage State Feedback Bulk-driven OTA for Wide Range Load Applications

This article employs a nested state feedback compensation technique to a three-stage bulk-driven operational transconductance amplifier (OTA). The projected OTA circuit consists of a bulk-driven PMOS amplifier, gate-driven NMOS amplifier, and common source (CS) amplifier. The entire transistors in the amplifier core are configuredwith self-cascode transistor topology to increase its output impedance. All transistors are designed to operate in a weak inversion in order to dissipate less power. Cross-coupled transistor pair topology in the bulk-driven stage allows to improve the effective transconductance of OTA. The CS amplifier can drive a large load capacitor. The polarities and transconductance gains of feedback blocks are controlled appropriately to obtain the desired DC gain and bandwidth. The capacitor-less compensation strategy allows the fabrication of the OTA using the minimum area. Conventional bulk-driven miler OTA, Bulk-driven stage improved indirect-feedback OTA (BSIF OTA), Gate-driven stage added bulk-driven OTA (GSIF OTA), and proposed bulk-driven OTA topologies are designed and simulated using cadence spectre tool at 25 mV supply voltage in the 65nm CMOS process. These OTA circuits are analyzed and compared in terms of parameters like DC gain, unity-gain frequency, phase margin, CMRR, power dissipated, slew rate, and input referred noise.

CCII+ Cell Based Instrumentation Amplifier Using BD-CM Gain Enhanced OTA

This paper presents the design of an instrumentation amplifier (IA) using second generation positive current conveyor which uses gain enhanced, bulk-driven, balanced current mirror, operational transconductance amplifier (OTA) cascaded with two CMOS inverters. First of all, a CMOS, bulk-driven current mirror OTA is designed and simulated in 180nm technology. For its performance enhancement, besides the current mirror topology, this OTA utilized the current starving technique which apply partial positive feedback (PPF) in active load side of OTA. Secondly, the conversion of this bulk-driven OTA into CCII plus cell is performed using inverters to yield its X and Z nodes. Finally, this CCII plus cell is used to design the IA. The gain of IA in differential input and single ended output configuration can be varied in the range of 10dB to 75dB. The various performance parameters of IA are simulated using Tanner EDA tool of 16.1 version in standard n-tub 180nm CMOS process technology node.

Biasing technique to improve total harmonic distortion in an ultra‐low‐power operational transconductance amplifier

This study presents a new technique based on large signal analysis, to enhance the total harmonic-distortion (THD) in an ultra-low-power operational transconductance amplifier (OTA). The proposed technique is used to implement an ultra-low-power gate-driven and bulk-driven OTA with high linear range. Mismatch and post-layout simulations in 0.13 μm CMOS technology demonstrate that the proposed technique can improve the THD and the dynamic range, without affecting the transconductance tuning and the common-mode control. It achieves a 183 and 640 mVpp linear ranges for gate-driven and bulk-driven OTA, and a 61.8 dB dynamic range at 0.5 V with 26.35 nW power dissipation.

Single-stage multipath class-AB bulk-driven OTA with enhanced power efficiency

A single-stage multipath class-AB bulk-driven operational transconductance amplifier working in weak inversion region with enhanced power efficiency is presented in this paper. The proposed bulk-driven amplifier makes use of four signal path to conduct small signal current, which leads to significant enhancement of transconductance when compared to conventional recycling structure. In addition, two of the signal paths build output stage operating at class-AB, resulting in a boost of slew rate. Most of all, the power efficiency of the proposed amplifier is improved over that of traditional recycling counterpart, enabling it more suitable for low-power applications. Simulated on SMIC 180 nm process, results demonstrate that the proposed bulk-driven amplifier achieves a 256% slew rate improvement and 100% unity-gain bandwidth enhancement when compared to the conventional recycling structure.

An ultra-low power high gain CMOS OTA for biomedical applications

An ultra-low power bulk-driven operational transconductance amplifier circuit for biomedical applications is presented. Higher DC gain and improved slew rate is achieved using double recycling technique, cross-coupled positive feedback configuration and driver transistors to enhance the transconductance of the conventional bulk-driven folded cascode amplifier. The post layout simulation of the proposed bulk-driven double recycling OTA in 180 nm CMOS technology, shows a 30 dB DC gain improvement and a 250% enhancement in GBW. The above results are validated using the Monte Carlo process variation and corner case simulations. The amplifier consumes 145 nW @ 0.6 V supply voltage.

Super class AB-AB bulk-driven folded cascode OTA

A super class AB-AB bulk-driven folded cascode operational transconductance amplifier (OTA) with improved slew rate and unity-gain bandwidth is presented. The proposed bulk-driven amplifier utilizes the adaptively biased circuits, the bulk-driven flipped voltage follower and quasi-floating gate circuit, to implement the class-AB input stage and class-AB output stage respectively, which provides enhanced unity-gain bandwidth and dynamic current boosting. The proposed bulk-driven OTA is simulated on the 0.18 μm SMIC process with 1 V low voltage supply. The simulation results show that the proposed class AB-AB bulk-driven OTA achieves the increased factor of 6.5 and 4.7 in unity-gain bandwidth and slew rate compared with that of conventional class-A counterpart with only 50% extra power consumption.

Low-voltage PVT-insensitive bulk-driven OTA with enhanced DC gain in 65-nm CMOS process

This paper presents a high DC gain bulk-driven operational transconductance amplifier (OTA) for low voltage applications. A cross-coupled active load is employed at the bulk-driven input stage to enhance the gain of OTA. A cross-forward (CF) gain stage was placed between the input and output stages of the OTA to enhance the output stage transconductance. The CF stage improves the phase margin of OTA and keeps the amplifier stable even for large capacitive loads (up to 50 pF) and also improves overall DC gain. The proposed OTA simulated using UMC 65-nm standard CMOS process, operates at a supply voltage of 0.5 V. Simulation results show that the OTA provides a gain of 72 dB at very low-frequencies. It has a phase margin of 74° and a unity gain frequency of 680 kHz for a load capacitance of 20 pF. Because of the bulk-driven input stage, the OTA achieved rail-to-rail input common-mode range. When the OTA simulated with a supply voltage of 0.35 V and load capacitance of 20 pF, the OTA provides a DC gain of 55 dB and a phase margin of 68° at a unity gain frequency of 617 kHz. The power dissipations were 3.03 μW and 1.56 μW for supply voltages of 0.5 V and 0.35 V, respectively. In comparison to previous works, the figure of merit of the proposed OTA has more than doubled in all respects.

Adjustably transconductance enhanced bulk‐driven OTA with the CMOS technologies scaling

An adjustably transconductance enhanced bulk-driven operational transconductance amplifier (OTA) working at weak inversion region is presented. Based on the traditional positive feedback source degeneration technique, a proposed current-shunt auxiliary amplifier is employed here to modulate the gate of input differential pairs, achieving a further improvement of the effective transconductance with the CMOS technologies scaling. In addition, an adjustable transconductance enhancement factor is obtained, leading to an enhanced stability performance. Both conventional and proposed bulk-driven OTAs are designed and simulated on CSMC 180 nm process. The simulated results demonstrate that the unity gain-bandwidth of the proposed bulk-driven OTA is improved by 120% compared to that of the conventional counterpart with a little neglected increased power consumption.

0.5 V, high gain two-stage operational amplifier with enhanced transconductance

ABSTRACTAn ultra-low-power, bulk-driven (BD) two-stage operational transconductance amplifier (OTA) operating in weak inversion region with enhanced transconductance is introduced. The aim is to boost the transconductance of OTA by using multiple current shunt auxiliary differential amplifiers in positive feedback through source degeneration circuits at input stage. The OTA employs a class AB amplifier at the output stage for high DC gain, while ensuring rail-to-rail operation. The overall OTA is realised in 180 nm complementary metal-oxide semiconductor standard process and its operation is validated through worst-case post-layout simulations at 0.5-V power supply. The OTA drives a maximum bias current of 48 nA achieving an open-loop DC gain of 78 dB, 1.6 μV/√Hz input referred noise at 1 kHz, total harmonic distortion of −66.35 dB and power consumption of 35 nW. The amplifier results in a remarkable improvement in slew rate, unity gain bandwidth and offers a transconductance of at least 10 times to that of conventional BD OTAs.

A 63‐dB gain OTA operating in subthreshold with 20‐nW power consumption

SummaryThis paper presents a two‐stage bulk‐driven operational transconductance amplifier operating in weak‐inversion region. The proposed amplifier is upgraded using recycling structure, current shunt technique, positive feedback source degeneration and indirect frequency compensation feedback to enhance transconductance under a reasonable stability. Combining these approaches leads to an ultra‐low‐power high performance amplifier without increasing power dissipation compared to the conventional one. Simulation results in 0.13‐µm complementary metal–oxide–semiconductor technology show the proposed structure achieves a 63‐dB DC gain at 0.25‐V supply voltage with just 20‐nW power dissipation. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Transconductance improvement technique for bulk‐driven OTA in nanometre CMOS process

A transconductance improvement technique for a bulk-driven operational transconductance amplifier (OTA) working in the weak inversion region is presented. Using the quasi-floating gate method, the proposed technique achieves larger transconductance improvement than conventional approaches with the CMOS technologies scaling. Moreover, its enhanced performance is at no expense of the power budget. Simulated on UMC 180 nm technology, the results demonstrate that the proposed bulk-driven OTA achieves more than two times gain–bandwidth improvement than that of the traditional counterpart with the same power.

Low-voltage bulk-driven OTA with enhanced transconductance and dc gain

A novel low-voltage bulk-driven operational transconductance amplifier (OTA) with enhanced transconductance and dc gain is presented. Based on the current-recycling structure and partial positive feedback technique, the effective transconductance of the bulk-driven input stage is improved. Also, the bulk-biasing technique is proposed to the composite transistor to achieve the dc gain enhancement. The proposed OTA is designed to operate with a 1 V supply using the CSMC 0.18 µm CMOS process. Results confirm that the gain–bandwidth achieves 29.6 MHz and the dc gain is higher than 86.1 dB when the load is 25.0 pF. The figure of merit is above 370, which demonstrates the proposed OTA has a significant boost compared to prior arts.

A 0.6-V 540-nW delta-sigma modulator for biomedical sensors

This paper presents an extremely low-power delta-sigma modulator for battery-powered biomedical sensors. Distributed feed-forward architecture is used to achieve efficient operation at a supply voltage of 0.6 V. In order to achieve a wide input range in this low voltage environment, the bulk-driven operational transconductance amplifier is designed with a self-cascode output stage. The modulator has a dynamic range of 52 dB with only 540 nW of power for the 250-Hz bandwidth. Such a significant reduction in power consumption allows diverse battery-powered biomedical applications that have limited battery power, such as the electro-oculogram, electroencephalogram, and electrocardiogram.

An Ultra Low-Voltage and Low-Power OTA Using Bulk-Input Technique and Its Application in Active-RC Filters

This paper presents the design of a two-stage bulk-input pseudo-differential operational transconductance amplifier (OTA) and its application in active-RC filters. The OTA was designed in 90 nm CMOS process and operates at a single supply voltage of 0.5 V. Using a two-path bulk-driven OTA by the combination of two different amplifiers the DC gain and speed of the OTA is increased. Rail-to-rail input is made possible using the transistor’s bulk terminal as in input. Also a Miller-Feed-forward (MFF) compensation is utilized which is improved the gain bandwidth (GBW) and phase margin of the OTA. In addition, a new merged cross-coupled self-cascode pair is used that can provide higher gain. Also, a novel cost-effective bulk-input common-mode feedback (CMFB) circuit has been designed. Simplicity and ability of using this new merged CMFB circuit is superior compared with state-of-the-art CMFBs. The OTA has a 70.2 dB DC gain, a 2.5 MHz GBW and a 70.8o phase margin for a 20 PF capacitive load whereas consumes only 25 µw. Finally, an 8th order Butterworth active Biquadrate RC filter has been designed and this OTA was checked by a typical switched-capacitor (SC) integrator with a 1 MHz clock-frequency.

A 0.8-V 816-nW delta–sigma modulator for low-power biomedical applications

This letter discusses the implementation of a low-voltage, low-power delta---sigma modulator as a sensing stage for biomedical applications. A distributed feed-forward structure and bulk-driven operational transconductance amplifier are used in order to achieve efficient operation at a supply voltage of 0.8 V. Instead of conventional low-voltage amplifier architectures, our design uses folded-cascode amplifiers, although they are not used in most low-voltage circuits. A wide input swing is achieved by using the bulk-driven approach, and the drawback of the limited voltage swing of the cascoded output stage is overcome by the distributed feed-forward modulator. The designed modulator has a dynamic range of 49 dB at a 0.8-V supply voltage and consumes only 816 nW of power for the 250-Hz bandwidth. The core chip size of the modulator is 1000 μm × 500 μm by using the 0.18-μm standard CMOS process.

A highly linear bulk-driven CMOS OTA for continuous-time filters

In this paper we present a bulk-driven CMOS triode-based fully balanced operational transconductance amplifier (OTA) and its application to continuous-time filters. The proposed OTA is linearly tunable with the feature of low distortion and high output impedance. It can achieve wide input range without compromising large transconductance tuning interval. Using a 0.18 ¼m n-well CMOS process, we have implemented a third-order elliptic low-pass filter based on the proposed OTA. Both the simulation and measurement results are reported. The total harmonic distortion is more than -45 dB for fully differential input signals of up to 0.8 V peak---peak voltage. A dynamic range of 45 dB is obtained under the OTA noise integrated over 1 MHz.