A Differential-to-Single-Ended Converter Based on Enhanced Body-Driven Current Mirrors Targeting Ultra-Low-Voltage OTAs

Abstract

In this work, an ultra-low-voltage (ULV) technique to improve body-driven current mirrors is proposed. The proposed technique is employed to improve the performance of conventional differential-to-single-ended (D2S) converters which at these low voltages suffer from a low common-mode rejection ratio (CMRR). In addition, the technique aims to improve the performance of the conventional D2S also under a large signal swing and with respect to the process, voltage and temperature (PVT) variations, resulting in a very low distortion, high current mirror accuracy and robust performance. An enhanced body-driven current mirror was designed in a 130nm CMOS technology from STMicroelectronics and an exhaustive campaign of simulations was conducted to confirm the effectiveness of the strategy and the robustness of the results. The enhanced D2S was also employed to design a ULV operational transconductance amplifier (OTA) and a comparison with an OTA based on a conventional D2S was provided. The simulation results have shown that the proposed enhanced D2S allows achieving the ULV OTAs with a CMRR and a PSRR which are 18 and 9 dB higher than the ones obtained with the conventional D2S topology, respectively. Moreover, the linearity performance is also improved as shown by the THD, whose value is decreased of about 5 dB.

A 0.3 V OTA with Enhanced CMRR and High Robustness to PVT Variations

“…The proposed OTA presents values of FOM S , CMRR, and noise that compare well to the state-of-the-art, and presents the best results in terms of linearity. The output stage was not optimized for slew rate, resulting in a low value of FOM L that is, however, comparable to some of the reported results [30,35,43].…”

“…The extremely low supply voltage does not allow for the exploitation of traditional design approaches such as tailed differential pairs and cascoding, and several design techniques have been studied for the design of efficient ULV OTAs. Solution based on a fully-digital approach (DIGOTA) [22][23][24] or operating in the time domain [25,26] have been proposed, but most of these techniques exploit analog approaches such as body-driving [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45], floating-gate [46] and floating-body [47] devices, and inverter-based architectures [48][49][50][51]. The latter are often suitable for implementation using digital standard-cell libraries [52][53][54][55], thus simplifying the layout through the use of automatic place-and-route CAD tools and easing design portability among different technologies.…”

“…A commonmode feedforward (CMFF) approach [29,38,[56][57][58] can be used to improve CMRR in typical conditions, also reducing variability under PVT. In [43], an improved body-driven current mirror was proposed and applied to a ULV differential-to-single-ended (D2S) converter stage to improve its CMRR; a similar idea was applied in [53] to achieve high CMRR in a standard-cell-based OTA. The idea was to exploit an auxiliary amplifier to attenuate the gain error of the current mirror.…”

“…This not only allows for improvement of the CMRR, but also for the achievement of a bias point that is robust under PVT variations, thanks to the reference voltage exploited by the auxiliary amplifiers. The proposed solution entails utilizing an enhanced gate-driven current mirror (previously published in a body-driven configuration [43]) alongside a biasing approach that accurately fixes current and voltage.…”

A Novel High Performance Standard-Cell Based ULV OTA Exploiting an Improved Basic Amplifier

“…The Operational Transconductance Amplifier (OTA) is widely used in a plethora of analog applications, and recently, several high-performance ULV OTAs exploiting body-driven [32]- [34], [36], [37], [43]- [46] and inverter-based [35], [47]- [51] architectures have been presented in the literature. All these OTAs require a full custom design approach in which the layout is carried out manually and often the area occupation is large because separate wells are needed for implementing body-driven stages.…”