A 0.3 V rail-to-rail ultra-low-power OTA with improved bandwidth and slew rate

In this paper, we present a novel operational transconductance amplifier (OTA) topology based on a dual-path body-driven input stage that exploits a body-driven current mirror-active load and targets ultra-low-power (ULP) and ultra-low-voltage (ULV) applications, such as IoT or biomedical devices. The proposed OTA exhibits only one high-impedance node, and can therefore be compensated at the output stage, thus not requiring Miller compensation. The input stage ensures rail-to-rail input common-mode range, whereas the gate-driven output stage ensures both a high open-loop gain and an enhanced slew rate. The proposed amplifier was designed in an STMicroelectronics 130 nm CMOS process with a nominal supply voltage of only 0.3 V, and it achieved very good values for both the small-signal and large-signal Figures of Merit. Extensive PVT (process, supply voltage, and temperature) and mismatch simulations are reported to prove the robustness of the proposed amplifier

An ultra-low-voltage class-AB OTA exploiting local CMFB and body-to-gate interface

In this work a novel bulk-driven (BD) ultra-low-voltage (ULV) class-AB operational transconductance amplifier (OTA) which exploits local common mode feedback (LCMFB) strategies to enhance performance and robustness against process, voltage and temperature (PVT) variations has been proposed. The amplifier exploits body-to-gate (B2G) interface to increase the slew rate and attain class-AB behaviour, whereas two pseudo-resistors have been employed to increase the common mode rejection ratio (CMRR). The architecture has been extensively tested through Monte Carlo and PVT simulations, results show that the amplifier is very robust in terms of gain-bandwidth-product (GBW), power consumption and slew rate. A wide comparison against state-of-the-art has pointed out that best small-signal figures of merit are attained and good large-signal performance is guaranteed, also when worst-case slew rate is considered

A Novel differential to single-ended converter for ultra-low-voltage inverter-based OTAs

For the design of inverter-based OTAs with differential input and single-ended output, the differential to single-ended (D2S) converter is a key building block. In fact, the performance of the D2S strongly affects the overall common-mode rejection ratio (CMRR) and input common-mode range (ICMR) of the whole OTA. In recent literature, inverter-based OTAs rely on a D2S topology based on an inverter driving another inverter with the input and output tight together which behaves as a “diode" connected device to implement a voltage gain approximately equal to -1. However, since this approach is based on the matching of the inverters, the performance of this D2S results sensitive to PVT variations if the bias point of the inverters is not properly stabilized. In this paper we present a novel topology of inverterbased D2S converter, exploiting an auxiliary, standard-cell-based, error amplifier and a local feedback loop. The proposed D2S, compared to the conventional one, exhibits higher CMRR, improved ICMR and better robustness with respect to PVT variations.We present also an ULV, standard-cell-based OTA, which exploits the proposed D2S converter and shows excellent performance figures of merit with low area footprint

A 0.3 V, rail-to-rail, ultralow-power, non-tailed, body-driven, sub-threshold amplifier

A novel, inverter-based, fully differential, body-driven, rail-to-rail, input stage topology is proposed in this paper. The input stage exploits a replica bias control loop to set the common mode current and a common mode feed-forward strategy to set its output common mode voltage. This novel cell is used to build an ultralow voltage (ULV), ultralow-power (ULP), two-stage, unbuffered operational amplifier. A dual path compensation strategy is exploited to improve the frequency response of the circuit. The amplifier has been designed in a commercial 130 nm CMOS technology from STMicroelectronics and is able to operate with a nominal supply voltage of 0.3 V and a power consumption as low as 11.4 nW, while showing about 65 dB gain, a gain bandwidth product around 3.6 kHz with a 50 pF load capacitance and a common mode rejection ratio (CMRR) in excess of 60 dB. Transistor-level simulations show that the proposed circuit outperforms most of the state of the art amplifiers in terms of the main figures of merit. The results of extensive parametric and Monte Carlo simulations have demonstrated the robustness of the proposed circuit to PVT and mismatch variations

CMOS current amplifiers : speed versus nonlinearity

This work deals with analogue integrated circuit design using various types of current-mode amplifiers. These circuits are analysed and realised using modern CMOS integration technologies. The dynamic nonlinearities of these circuits are discussed in detail as in the literature only linear nonidealities and static nonlinearities are conventionally considered. For the most important open-loop current-mode amplifier, the second-generation current-conveyor (CCII), a macromodel is derived that, unlike other reported macromodels, can accurately predict the common-mode behaviour in differential applications. Similarly, this model is used to describe the nonidealities of several other current-mode amplifiers because similar circuit structures are common in such amplifiers. With modern low-voltage CMOS-technologies, the current-mode operational amplifier and the high-gain current-conveyor (CCII∞) perform better than open-loop current-amplifiers. Similarly, unlike with conventional voltage-mode operational amplifiers, the large-signal settling behaviour of these two amplifier types does not degrade as CMOS-processes are scaled down. In this work, two 1 MHz 3rd -order low-pass continuous-time filters are realised with a 1.2 μm CMOS-process. These filters use a differential CCII∞ with linearised, dynamically biased output stages resulting in performance superior to most OTA-C filter realisations reported. Similarly, two logarithmic amplifier chips are designed and fabricated. The first circuit, implemented with a 1.2 μm BiCMOS-process, uses again a CCII∞. This circuit uses a pn-junction as a logarithmic feedback element. With a CCII∞ the constant gain-bandwidth product, typical of voltage-mode operational amplifiers, is avoided resulting in a constant 1 MHz bandwidth with a 60 dB signal amplitude range. The second current-mode logarithmic amplifier, based on piece-wise linear approximation of the logarithmic function by a cascade of limiting current amplifier stages, is realised in a standard 1.2 μm CMOS-process. The limiting level in these current amplifiers is less sensitive to process variation than in limiting voltage amplifiers resulting in exceptionally low temperature dependency of the logarithmic output signal. Additionally, along with this logarithmic amplifier a new current peak detectoris developed.reviewe

A Robust 96.6-dB-SNDR 50-kHz-Bandwidth Switched-Capacitor Delta-Sigma Modulator for IR Imagers in Space Instrumentation

Infrared imaging technology, used both to study deep-space bodies' radiation and environmental changes on Earth, experienced constant improvements in the last few years, pushing data converter designers to face new challenges in terms of speed, power consumption and robustness against extremely harsh operating conditions. This paper presents a 96.6-dB-SNDR (Signal-to-Noise-plus-Distortion Ratio) 50-kHz-bandwidth fourth-order single-bit switched-capacitor delta-sigma modulator for ADC operating at 1.8 V and consuming 7.9 mW fit for space instrumentation. The circuit features novel Class-AB single-stage switched variable-mirror amplifiers (SVMAs) enabling low-power operation, as well as low sensitivity to both process and temperature deviations for the whole modulator. The physical implementation resulted in a 1.8-mm 2 chip integrated in a standard 0.18-μm 1-poly-6-metal (1P6M) CMOS technology, and it reaches a 164.6-dB Schreier figure of merit from experimental SNDR measurements without making use of any clock bootstrapping, analog calibration, nor digital compensation technique. When coupled to a IR imager, the current design allows more than 50 frames per minute with a resolution of 16 effective number of bits (ENOB) while consuming less than 300 mW