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The paper presents a novel shunt voltage regulation architecture that uses an RF power detector, based on Pulse Width Modulation (PWM) technique, aiming at magnetic coupled Radio-Frequency Identification (RFID) transponders. The proposed regulator architecture implements two feedback loops: a voltage clamping circuit that composes a fast correction loop and a slow but accurate power detector loop. The first clamping loop guarantees fast over-voltage protection, mainly in high RF power condition (short reading distance), but degrades power efficiency when in low power condition (large reading distance). The second loop corrects the imprecision of the first loop according to the detected RF input power. Therefore, it increases power efficiency and reading distance when in low RF power condition. The RF power detector architecture, based on a PWM technique, and the shunt regulator design are presented and discussed in detail. RFID power regulation issues are also discussed, followed by a brief review of RF power detector circuits. The complete regulator architecture was implemented in a 180nm CMOS low cost process and prototyped as part of a commercial low-frequency (134 kHz) RFID transponder. The complete transponder area is 870×870 μm2, being 130×230 μm2 related to the regulator circuit only. Both resonant and supply capacitors are implemented on chip. The analog and digital functional blocks of the RFID system consume 4.5 μW. Performance of the transponder is measured with the shunt regulator enabled and compared with the power limiting approach using only clamping diodes. Measured results show an improvement of 16.7% in the maximum communication distance between the transponder and the reader because of the proposed regulation strategy.

This work presents the design of a low voltage dynamic comparator for low-power ADC applications. The dynamic comparator uses a pre-amplifier powered by a floating reservoir capacitor and a positive feedback bulk structure. The output stage comprises a simple circuit to reduce the total voltage overhead necessary to define the logic levels. The powering scheme of the pre-amplifier, with a floating reservoir capacitor, contributes to reduce the impacts of global process variability. The positive feedback bulk structure lowers the threshold voltages of the pre-amplifier transistors at the sampling phase. Such structure also provides positive feedback signal during the comparison phase to provide extra transconductance. The proposed dynamic comparator is designed and simulated in a 28 nm CMOS technology and reaches an IRN below of the quantization noise of a 10 bits differential ADCs working with 600 mV power supply. The dynamic comparator achieves 237 μV input-referred noise, while consuming only 38.8 fJ per comparison and having a nominal delay of 5.77 ns.

In this paper a self-biased current reference based on Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) Zero Temperature Coefficient (ZTC) condition is proposed. It can be implemented in any Complementary Metal-Oxide-Semiconductor (CMOS) fabrication process and provides another alternative to design current references. In order to support the circuit design, ZTC condition is analyzed using a MOSFET model that is continuous from weak to strong inversion, showing that this condition always occurs from moderate to strong inversion in any CMOS process. The proposed topology was designed in a 180 nm process, operates with a supply voltage from 1.4V to 1.8 V and occupies around 0.010mm2 of silicon area. From circuit simulations our reference showed a temperature coefficient (TC) of 15 ppm/oC from -40 to +85oC, and a fabrication process sensitivity of σ/μ = 4.5% for the current reference, including average process and local mismatch variability analysis. The simulated power supply sensitivity is estimated around 1%/V.

This paper presents a power-efficient Ultra Low Voltage (ULV) Fully-Differential (FD) Digital-Based Operational Transconductance Amplifier for Biomedical signal processing (BioDIGOTA), which digitally processes biological analog signals using CMOS standard-cells. Post-layout simulations, including parasitic effects in 180nm CMOS technology, show that BioDIG- OTA consumes only 144 nW at 300 mV of supply voltage while driving a 20 pF capacitive load, with a power efficiency factor (PEF) lower than 1. The layout occupies 0.03 mm2 total silicon area, excluding I/0 pads. The proposed BioDIGOTA proves that digital-based analog design can be adopted in biomedical signal amplifiers, lowering the total silicon area by 2.3X times compared to the current state of the art landscape while keeping reasonable power and system performance.

An ultra-low voltage and ultra-low power Digital-Based Operational Transconductance Amplifier (DB-OTA) is presented and demonstrated on silicon in 180 nm CMOS. The DB-OTA is designed using digital standard cells, hence benefitting from technology scaling as much as digital circuits, while also being technology- and design-portable, and requiring minimal design and integration effort compared to conventional analog-intensive OTAs. The fabricated DB-OTA testchip occupies a compact area of 1,426 $\mu \text{m}^{2}$ , operates at supply voltages down to 300 mV, and consumes only 590 pW while driving a capacitive load of 80pF. Its measured Total Harmonic Distortion (THD) is lower than 5% at a 100-mV input signal swing. Based on these results, the proposed DB-OTA achieves 2,101 V−1 small-signal figure of merit (FOMS) and 1,070 large-signal figure of merit (FOML). To the best of the authors’ knowledge, the power is the lowest reported to date in an OTA, and the achieved figures of merit are the best in sub-500 mV OTAs reported to date. The low cost, the low design effort and the high power efficiency of DB-OTA make it well suited for purely harvested low-frequency analog interfaces in sensor nodes.

This paper presents a non-linear shunt regulator based on a PWM RF power detector for RFID applications. The shunt regulator is composed of two feedback loops. The first is a fast loop based on a simple RF voltage clamp that guarantees overvoltage protection for the internal circuits. The second is an accurate loop based on a power detector circuit that slowly corrects the first loop errors according to the input RF power. The theoretical formulation of the RF-to-DC conversion in the power detector is presented and compared to a high-level implementation. A small-signal model of the complete shunt regulator was developed to assist in the CMOS circuit design. The regulator is part of a commercial low-frequency RFID transponder. It shows an improvement of 16.7 % in the maximum communication distance of the transponder with the shunt regulator enabled when compared to the previous power limiting approach using only clamping diodes.

Electromagnetic interference (EMI) disturbances coupled in the power supply of voltage and current references can severely degrade their performance, due to its finite power supply rejection (PSR). The design of a 90-dB PSR 4-dBm EMI-resistant NMOS-only voltage reference is herein presented. The voltage reference is designed based on the zero-temperature-coefficient transistor operating point. The high PSR is obtained using zero- $V_{T}$ transistors as active loads in the open and feedback loop of the circuit. Two versions, using standard $V_{T}$ and low-power $V_{T}$ transistors, were designed in a 130-nm CMOS process. Both are designed using the same thermal compensation principle. The circuits occupy 0.014 and 0.006 mm $^{2}$ of silicon area while consuming around 1.15 and 0.156 $\mu$ W at 27 $^\circ$ C, respectively. Postlayout simulations present a reference voltage of 206 and 450 mV with an average temperature coefficient of 321 and 86 ppm/ $^\circ$ C (1000 samples), under a temperature range from $-$ 55 to 125 $^\circ$ C. An EMI source of 4 dBm (1 $\text{V}_{\text{pp}}$ ) injected in the power supply, according to the direct power injection standard, yields $-$ 0.17% and $-$ 0.1 ${\%}$ of the maximum dc shift and 822 and 950 $\mu \text{V}_{\text{pp}}$ of the maximum peak-to-peak ripple for the standard $V_{T}$ and low-power $V_{T}$ implementations, respectively.

This work presents a resistorless self-biased and small area sub-bandgap voltage reference that works in the nano-ampere consumption range with 0.75 V of power supply. The circuit applies a curvature compensation technique that allows an extended temperature range without compromising the temperature stability. The behavior of the circuit is analytically described, and a design methodology is proposed which allows the separate adjustment of the bipolar junction transistor bias current and its curvature compensation. Simulation results are presented for a 180 nm CMOS process, where a reference voltage of 469 mV is designed, with a temperature coefficient of 5 ppm/°C for the ź40 to 125 °C extended temperature range. The power consumption of the whole circuit is 16.3 nW under a 0.75 V power supply at 27 °C. The estimated silicon area is 0.0053 mm2.

This work presents the design of a narrowband Low Noise Amplifier (LNA) that is a part of a transponder project of a UHF satellite for the Brazilian Environmental Data Collecting System (SBCDA). The proposed LNA operates at 401.635 MHz moreover, it provides 28dB of power gain, 3.6dB of noise figure (NF), IIP3 of -28 dBm and 6.53 mW of power consumption and it was designed in a standard 130 nm CMOS process.

This paper presents a power-efficient Ultra Low Voltage (ULV) Digital-Based Operational Transconductance Amplifier (DB-OTA), which uses static logic gates and processes digitally the analog input signal. Post-layout simulations in 180nm CMOS technology show that at 300mV supply voltage the circuit consumes just 2nW while driving a capacitive load of 80pF with Total Harmonic Distortion lower than 5% at 100mV input signal swing. The total silicon area is $1,426\ \mu \mathrm{m}^{2}$ . The maximum energy efficiency supply for the DB-OTA and its scalability to 40nm CMOS technology node are also demonstrated.

In this work a resistorless sub-bandgap voltage reference topology is presented. It is a self-biased and small area circuit that works in the nano-ampere consumption range, and under 1 V of power supply. The behavior of the circuit is analytically described, a design methodology is proposed and simulation results are presented for two CMOS processes, XFAB 0.18 μm and IBM 0.13 μm. Experimental results from one fabrication run demonstrate a reference voltage of 570 mV, with a temperature coefficient as low as 11 ppm/°C for the 0---125 °C range, while the power consumption of the whole circuit is 5 nW under a 0.9 V supply at 27 °C. The occupied silicon area is 0.0022 mm$$^2$$2.

This work presents an ultra-low power low-voltage high-order temperature-compensated voltage reference. The proposed circuit is based on the self-cascode MOSFET (SCM) and explores the dependence of the threshold voltage (V T ) with the transistor dimensions. The SCM is biased by the leakage current of a zero-V T transistor for PSRR improvement. The proposed circuit is composed only of 3 transistors. The high-order temperature compensation is achieved through a bulk-driven scheme. Additionally, the proposed high-order compensation also attenuates the mismatch variability of the voltage reference. Post-layout simulation results for a standard 130 nm CMOS process are presented. A voltage reference of 90.5 mV with a 1 ppm/°C temperature coefficient (TC) is achieved at typical corner. The circuit can operate at a minimum supply voltage as low as 0.3 V while consuming 43.7 pW at room temperature.

This work presents a fully integrated single-stage 2.4 GHz power amplifier (PA) that was designed in a 180nm CMOS process using a power combining technique to achieve higher output power. A series combining transformer (SCT) combines two cascode differential amplifiers and makes extensive use of virtual AC ground nodes to reduce the impact of bond-wire parasitics. The center-taps of the output transformers are used for 2nd harmonic impedance tuning inside the chip. In post-layout simulation the PA uses a 3.3 V power supply and achieves 24dBm maximum output power at a peak drain efficiency of 23.4%. The test chip returned recently from fabrication and it will undergo electrical tests soon.

A nano-ampere current reference with temperature compensation operating is presented. The reference current is generated biasing a zero-VT transistor near its Zero-temperature coefficient (ZTC) point. Two versions were implemented in a 180 nm CMOS process. Both are designed using the same thermal compensation principle, but the second version uses an auxiliary circuit to compensate process variation. The circuits occupy 0.01 and 0.018 mm2 of silicon area while consuming around 30.5 and 122 nW at 27° C, respectively. Post-layout simulations present a reference current of 10.86 and 10.95 nA with a average temperature coefficient of 108 and 127 ppm/°C (100 Samples), under a temperature range from −20 to 120 °C, and a line sensitivity of 0.54 and 0.86 %/V at 0.9 V to 1.8 V of supply voltage, respectively.

This work presents a six phase Switched Capacitor (SC) DC — DC converter for photovoltaic Energy Harvesting designed in a 130 nm CMOS process for commercial motes application and Internet of Things (IoT). It tracks the Maximum Power Point (MPP) of a commercial 3 cm × 3 cm 60 mW poly-crystalline photoelectric panel through switching frequency modulation aiming battery recharge. Open-circuit voltage ratio was the chosen Maximum Power Point Tracking (MPPT) strategy. The converter achieves a maximum power conversion efficiency of 90 % for input power higher than 30 mW and is designed to operate with input voltages from 1.25 V to 1.8 V, resulting output voltages from 2.5 V to 3.6 V, respectively. Peripheral circuitry also includes an output over-voltage protection of 3.6 V and the control circuits, that consumes a total of 850 μA at 3.3 V. Complete layout consumes 300 × 700 μm2 of silicon area. The only external components are 6×100 nF capacitors.

This paper presents a 300 MHz to 3 GHz Low-Noise Amplifier (LNA) with high HP3 and one of the smallest silicon area we could find. It is based on a single amplifier, where it is systematically optimized to achieve better results than more complex noise canceling topologies, thus, saving area and power consumption. A CMOS inverter with resistive feedback where transistors are self-biased in strong inversion is designed and optimized for low NF and high IIP3 and then the feedback resistor is calculated for input impedance matching. The post-layout simulation results in a 130 nm process show for the entire bandwidth a voltage gain around 12 to 15 dB, a NF < 3.6 dB, a Sii of −15.2 to −10.5 dB, HP3 of 4.7 to 5.3 dBm, total area of 40 um × 30 um and power consumption of 6.5 mW under 1.2 V supply. Monte Carlo simulations for 1000 samples show IIP3 of 3.3 to 6 dBm with σ of 0.48 dBm.

This paper presents a self-biased self-cascode MOSFET (SBSCM) voltage reference that can operate with supply voltages as low as 0.45 V while consuming tens of pW. The voltage reference is generated through the self-cascode MOSFET (SCM) using transistors with different threshold voltages and is implemented in a way that the SCM itself composes the bias circuitry. The proposed topology was implemented in a standard 0.18 μm CMOS process and post-layout simulation results in a reference voltage of 248 mV with temperature coefficient around 7 ppm/oC for the 0 oC to 125 oC range, while consuming 93 pW at room temperature with 0.45 V of supply voltage. The occupied silicon area is 0.002 mm2.

The design of an ultra-low voltage CMOS wideband LNA topology operating under a 0.6 V power supply with high gain and high IP2 is presented in this paper. The circuit performance is targeted towards use in direct conversion receivers, where a high IP2 is required. The LNA operates in sub-1 GHz applications reaching frequencies as low as 50 MHz, as it is required by IEEE 802.22 standard. The topology proposed here is based on the resistive-feedback inverter with a cascaded auxiliary amplifier to implement noise canceling. This cascaded amplifier is composed by a common-source (CS) amplifier and a very linear buffer at the output of the cascade. The high IP2 is obtained by a proper transistor biasing and by combining diodes with the load of the amplifiers with the highest non-linearity. This topology also works as a balun to comply with single-ended input from antennas and differential mixers as output loads. The post-layout simulations included bondwire inductances and pad capacitances parasitics. The results show a bandwidth of 50 MHz–1 GHz, voltage gain > 18 dB, NF < 3.8 dB, Sn < −13 dB and maximum IP2 of 38 dBm. The LNA power consumption is just 6.7 mW, excluding pad buffers.

In this paper, we present a VCO designed for operation at 250 mV dissipating 590 nW, free running frequency of 462 kHz with voltage-to-frequency maximum non-linearity of 0.33%. The VCO design aim to a time based ADC, whose resolution is highly limited by the non-linearity of the VCO itself, which may be corrected by further digital calibration. The proposed VCO uses a ring oscillator topology and employs forward body biasing to achieve high linearity in the analog domain.

This paper presents a MOS-only high power supply rejection (PSRR) voltage reference with a very low temperature coefficient (TC) that consumes only tens of nano-Watt. It is composed by a threshold voltage monitor circuit with no resistors, cascaded with a thermal voltage generator, adequate for fabrication in standard processes. Since the MOS transistors operate in subthreshold and near-threshold regimes the current consumption is very low. The operation of the circuit is analytically described and a design methodology is proposed. Post-layout simulations for a design in a 130 nm CMOS process are presented, resulting a reference voltage around 670 mV with a best case TC of 1.5 ppm/°C for the −40 to +125 °C range and an average TC of 20 ppm/°C over process variations, untrimmed. A very low sensitivity to VDD is achieved, resulting a PSRR lower than −71 dB at 100 Hz and a line sensitivity (LS) lower than 576 ppm/V for a supply range from 1 to 3 V. The area is very small, 0.0084 mm2 including the start-up stage.

In this work a novel resistorless MOSFET 3-transistor voltage reference that operates in the picowatt range and occupies very small area is proposed. The circuit is based on a self-cascode structure that is biased in subthreshold condition using the leakage current provided by a reverse biased MOSFET diode. Its electrical behavior is analytically described and a design methodology is presented to allow the transistors sizing for optimal temperature compensation. Simulation results for a standard 130 nm CMOS process are presented to validated the proposed circuit topology. A reference voltage of 85 mV is obtained with a temperature coefficient (TC) of 17.4 ppm/°C and consuming only 7 pW under 0.3 V of power supply at room temperature. Monte Carlo analysis shows that the reference voltage σ/μ< 3.3% and that 90% of the samples present TC

This paper proposes a 2.2 GHz CMOS Power Amplifier (PA) useful to S-Band applications with an effective 3-bit output power control for efficiency improvement. It uses an input transformer to reduce ground bounce effects and operates around 1 W of output power. A tuned driver stage provides impedance matching to the input signal source and proper gain to the next stage. A control stage is used for efficiency improvement, composed by four parallel branches where the state (on or off) of 3 branches is separately activated by a 3-bit input. The classE power stage uses a cascode topology to minimize the voltage stress over the power transistors, allowing higher supply voltages. The PA was designed in a 130 nm RF process and post-layout simulations resulted a peak output power of 28.5 dBm with a maximum power added efficiency (PAE) around 47% under 3.3 V of supply voltage. The 3-bit control allows a total output power dynamic range adjustment of 12.4 dB, divided in 8 steps, with the PAE changing from 13.4% to 47.3%.

This paper presents an alternative to crystal based oscillators for reference frequencies in highly integrated SoCs. The frequency reference through the usage of an active bias controlled ring oscillator operating with a supply voltage from 300 to 500 mV for an temperature from −40 to 125 ° C. The oscillator shows a very good temperature and supply voltage frequency stability coming from the active biasing using a stable current reference.

Electromagnetic Interference (EMI) disturbances coupled in the power supply of voltage and current references can severely degrade their performance, due to its finite Power Supply Rejection Ratio (PSRR). The design of a 90 dB PSRR, 4 dBm EMI resistant NMOS-Only Voltage Reference is herein presented. The Voltage Reference is designed based on the Zero Temperature Coefficient (ZTC) transistor point. The high-PSRR is obtained using zero-VT transistors as active loads in the open and feedback loop of the circuit. The final circuit was designed in a 130 nm CMOS process and occupies around 0.014 mm2 of silicon area while consuming just 1.15 μW. Post-layout simulations present a 206 mV of Voltage Reference with a Temperature Coefficient of 321 ppm/°C, for the temperature range from −55 to 125 °C. An EMI source of 4 dBm (1 V pp ) injected in the power supply, according to the Direct Power Injection (DPI) standard, yield in a maximum dc shift and Peak-to-peak ripple of −0.17 % and 822 μV pp , respectively.

Electromagnetic Interference (EMI) degrades the performance of voltage and current references, due to its finite Power Supply Rejection Ratio (PSRR). The design of a 90 dB PSRR, 4 dBm EMI resistant MOSFET-Only Voltage Reference is herein presented. The Voltage Reference is designed based on the Zero Temperature Coefficient (ZTC) transistor point. The high-PSRR is obtained using zero-VT transistors as active loads in the open and feedback loop of the circuit. The final circuit was designed in a 130 nm CMOS process and occupies around 0.014 mm2 of silicon area while consuming just 1.15 μW. Postlayout simulations present a 206 mV of Voltage Reference with a Temperature Coefficient of 321 ppm/° C, for the temperature range from −55 to 125 ° C. An EMI source of 4 dBm (1 Vpp) injected in the power supply, according to the Direct Power Injection (DPI) standard, yield in a maximum DC Shift and Peak-to-Peak ripple of −0.17 % and 822 μVpp, respectively.

This work presents the design of a 6 bits M-2M ladder Digital-to-Analog Converter (DAC) proper for operation under supply voltages of 200 mV or lower. Since the MOS transistors are operating in the subthreshold region under such low supply, the mismatch analysis was done using an all-region continuous MOSFET model. The performance of the circuit is evaluated through simulations and the trade-offs between linearity, supply voltage and sampling rate are investigated in the paper. It is proposed that a 6 bits M-2M DAC operating under 200 mV and with sampling rate of 5.1MS/s is feasible using a commercial 130 nm process and standard transistors.

This paper proposes a 2.2 GHz CMOS Power Amplifier (PA) useful to S-Band applications with an effective 3-bit output power control for efficiency improvement. It is composed by a cascode amplifier topology to minimize the voltage stress across the power transistors, being the cascode amplifier composed by four parallel branches, where the state (on or off) of 3 branches is separately activated by a 3-bit input, for efficiency control. It was designed for the 1 W output power range in 130 nm CMOS process. Post-layout simulations resulted a peak output power of 28.1 dBm (near 650 mW) with a maximum output power efficiency around 43% under 3.3 V of supply voltage. The 3-bit control allows a total output power dynamic range adjustment of 5.7 dBm, divided in 7 steps, with the efficiency changing from 25.4% to 43.7%.

This work presents a 2-decades wideband (15.5 MHz–1.55 GHz) low-noise amplifier (LNA) circuit. As its wideband range extends from HF to UHF, it includes, among others, the ISM bands (27.12 MHz, 40.7MHz, 434.79 MHz, 928 MHz), the GSM850 and GSM900 bands, and IEEE 802.22 WRAN bands (54 MHz–862 MHz). The proposed circuit operates also as a balun (single-ended input — differencial output) and its layout presents a very small area, an important savings resulting from this inductorless design for the LNA. An auxiliary amplifier was introduced so that a high gain and a high IIP3 can be achieved with low Noise Figure (NF). The linearity was improved using a distortion cancellation strategy and the NF was improved through a noise canceling technique. The amplifier was implemented in a 130 nm CMOS process, using a PDK from Silterra foundry, in a compact 77μm × 54μm core area. Simulations including post-layout parasitics, bondwire, ESD protection and PAD input parasitics resulted (over the entire band) in a voltage gain of 20.8–24.9 dB, a noise figure (NF) of 2.7–3.7 dB, an input power reflection coefficient Sn < −11.4 dB, an input third-order intercept point (IIP3) = −0.4 dBm (@750MHz), and a power consumption of 10.4 mW under 1.2 V supply. This balun LNA shows a worst case gain imbalance between outputs of 1.2 dB and very low sensitivity to temperature variations for gain, NF and Sn in the range of 0 to 85°C.

This work presents a high PSRR nano-watt resistorless thresh old voltage (VTo) monitor circuit that can be used in temperature sensors, voltage and current references, radiation dosimeters and other applications such as fabrication process monitoring and verification. In this circuit design the MOS transistors operate in subthreshold and near-threshold regimes, the circuit analysis is based on a current-voltage relationship derived from a continuous physical MOSFET model, valid from weak to strong inversion. The bias condition is established from the equilibrium between two self-cascode cells operating at different inversion levels, and the high PSRR results from a high gain feedback path. The circuit is MOSFET-only, and can be implemented in any standard digital CMOS process. Post-layout simulations show that it operates with less than 1 V of power supply, consuming only tens of nW, and resulting in a VT0 error lower than 1%, when compared to its modeling value, for a −40 to +125°C temperature range. A very high rejection to VDD variation is achieved in this design, with PSRR lower than −63.9 dB at 100 Hz, and a line sensitivity lower than 252 ppm/V was found for a supply range from 1 V to 3 V. Monte-Carlo simulations are presented to evaluate the fabrication variability sensitivity, presenting a maximum error of 4% for a 3a spread range. The circuit area is very small, around 0.0047 mm2 including the start-up stage.

This work presents a self-biased MOSFET threshold voltage V T0 monitor. The threshold condition is defined based on a current-voltage relationship derived from a continuous physical model. The model is valid for any operating condition, from weak to strong inversion, and under triode or saturation regimes. The circuit consists in balancing two self-cascode cells operating at different inversion levels, where one of the transistors that compose these cells is biased at the threshold condition. The circuit is MOSFET-only (can be implemented in any standard digital process), and it operates with a power supply of less than 1 V, consuming tenths of nW. We propose a process independent design methodology, evaluating different trade-offs of accuracy, area and power consumption. Schematic simulation results, including Monte Carlo variability analysis, support the V T0 monitoring behavior of the circuit with good accuracy on a 180 nm process.

Digital and analog ICs generally rely on the concept of matched behavior between identically designed devices. Time-independent variations between identically designed transistors, called mismatch, affect the performance of most analog and even digital MOS circuits. This article focuses on the analysis of mismatch in MOS transistors resulting from random fluctuations of the dopant concentration, first studied by Keyes. Today, we recognize these fluctuations as the main cause of mismatch in bulk CMOS transistors.

This work presents a study of the CMOS based R-2R ladder network (also called M-2M) Digital-to-Analog Converter (DAC) as a potential candidate for ultra-low voltage (ULV) applications, i.e. supply voltages VDD lower than 200mV. MOS transistors operate in subthreshold under such very low VDD, and the circuit analysis must be done using an all-region continuous MOSFET model. Simulation results in a commercial 130 nm process corroborate the presented analysis, showing that it is possible to implement this DAC topology for 6 to 8 bits operating under supply voltages from 70 mV to 140 mV.

This paper describes the design and implementation of a low-pass third-order single-loop single-bit continuous-time sigma-delta modulator (CT-SDM) in a 130 nm CMOS process. To reduce clock jitter effects and operational amplifiers requirements a non-return-to-zero (NRZ) digital-to-analog converter (DAC) pulse shape was employed. Post-layout simulation results indicate that the modulator achieves 56 dB of dynamic range, 57.31 dB of peak SNDR or 9.23 bits of effective resolution over a 1 MHz signal bandwidth with an oversampling ratio (OSR) of 64. The CT-SDM draws 5.91 mW from a 1.2 V power supply providing a figure-of-merit (FOM) of 4.93 pJ/conv. The CT-SDM core area is 0.31 mm2 and the chip was manufactured and will be soon characterized.

The MOSFET Zero Temperature Coefficient (ZTC) condition is a strategy that can be used to implement low temperature sensitivity circuits, such as current and voltage references. This condition is usually analyzed using the strong inversion quadratic MOSFET model. In this work we use a different approach, based on a continuous MOSFET model that can predict its behavior from weak to strong inversion. Based on this analysis, we verify that the ZTC point occurs from moderate to strong inversion for any CMOS process, since this point must occur for gate-source voltages larger than one threshold voltage. Also, a resistorless switched capacitor current reference based on the ZTC condition (ZSCCR), presenting low temperature coefficient (TC), is presented. The ZSCCR is designed in a 180 nm process, resulting a reference current of 5.88 µA under a supply voltage of 1.8 V, and occuping a silicon area around 0.010mm2. Results from circuit simulation show an effective temperature coefficient (TC eff ) of 60 ppm/°C from −45 to +85 °C and a power consumption of 63 µW.

The continuous scaling of CMOS devices has required the consequent reduction of the supply voltages. There is a need for analog and RF circuits able to operate under at supplies lower than 0.5 V. This paper presents a voltage reference based on the MOSFET zero-temperature condition (ZTC) that operates with a low 0.5 V supply. The circuit is composed by a diode-connected MOS transistor operating near the ZTC condition that is biased by a proportional-to-absolute-temperature (PTAT) current reference implemented with Schottky-diodes. The ZTC condition is analysed using a continuous MOSFET model that is valid from weak to strong inversion and the circuit behaviour is described by theoretical expressions. Our reference circuit is designed for 3 versions: each with MOSFETs of different threshold voltage (standard-VT, low-VT, and zero-VT), all available in the 130 nm CMOS process used. These designs result in three different and very low reference voltages: 312, 237, and 51 mV. All 3 designed reference operate in the range of 0.45 to 1.2 V of supply voltages, consuming 1 uA of typical supply current. Post-layout simulations present a Temperature Coefficients (TCs) of 214, 372, and 953 ppm/°C in a temperature range from -55 to 125°C, respectively. Monte-Carlo simulations show the fabrication variability impact on the circuit performance. The voltage reference was designed in a 130 nm process and it uses 0.014 mm2 of silicon area.

The necessary conditions to design MOSFET transconductors with low temperature dependence are analysed and defined in this paper. Transconductors, or Gm circuits, are fundamental blocks used to implement adjustable filters, multipliers, controlled oscillators, amplifiers and a large variety of analog circuits. Temperature stability is a must in such applications, and herein we show a strategy that can be used to improve the temperature stability of these transconductors by biasing MOSFETs at transconductance zero-temperature condition (GZTC). This special bias condition is analysed using a MOSFET model which is continuous from weak to strong inversion, and it is proved that this condition always occurs from moderate to strong inversion operation in any CMOS fabrication process. Additionally, a few example circuits are proposed using this technique: a single-ended resistor emulator, an impedance inverter, a first order and a second order filter. These circuits were simulated in a 130 nm CMOS commercial process, resulting improved thermal stability in the main performance parameters, in the range from 27 to 53 ppm/°C.

This work presents a self-biased MOSFET threshold voltage V T0 extractor circuit. Its working principle is based on a current-voltage relationship derived from a continuous physical model. The model is valid for any operating condition, from weak to strong inversion, and under triode or saturation regimes. The circuit is MOSFET-only (can be implemented in any standard digital process), and it operates with a power supply of less than 1 V, consuming tenths of nW. Post-layout simulation results show that the extracted V T0 has an error inferior to 1.3%, when compared to the theoretical value, for a −40 to 125°C temperature range. We present variability results from Monte Carlo simulations that support the extracting behavior of the circuit with good accuracy. The occupied silicon area is 0.0076 mm2 in a 0.13µm CMOS process.

This paper presents a high-linearity and large output swing instrumentation amplifier for portable multichannel biomedical applications. It is composed of a fully differential two-stage CMOS amplifier in which a feedback provides stable signal gain that can be adjusted from 25 to 100 V/V. Additionally, a pseudo-resistive feedback combined with an appropriate input capacitive coupling provides a high-pass behavior, presenting a −3 dB cut-off frequency lower than 120 mHz. The amplifier is fully integrated in a 130 nm CMOS process, using only 0.1 mm2 of silicon area, including large matched capacitor banks. Its power consumption is 31.3 µW under a 1.5 V supply. The pre-amplifier gain reaches less than 0.02 % of THD (total harmonic distortion) for an output swing of 2 Vpp in post-layout simulations. The total input-referred noise estimated from simulations is 1.93 µVrms inside the 0.5 Hz to 500 Hz frequency range.

A MOSFET-only sub-bandgap voltage reference at less than 50 nW and with very low temperature coefficient is introduced. It consists of a threshold voltage extractor circuit and a proportional to absolute temperature voltage generator, using no resistors. The behavior of the circuit is analytically described, a design methodology is proposed and simulation results for a 0.13 µm CMOS process are presented. It allows a reference voltage below the bandgap, 625 mV in this design example, achieving a temperature coefficient of 2.3 ppm/°C for the -40 to 125 °C temperature range. The circuit consumes 40 nW at 27°C and under 1.2 V supply, being the implemented silicon area 0.0099 mm².

In this work a novel resistorless sub-bandgap voltage reference (BGR) is introduced. It is a self-biased and small area topology that works in the nano-ampere current consumption range, and under 1 V of power supply. The analytical behavior of the circuit is described, and simulation results for a standard 0.18 μm CMOS process are analysed. A reference voltage of 479 mV is demonstrated, with a temperature coefficient of 8.79 ppm/oC for the 0 to 125 °C range, while the power consumption of the whole circuit is 4.86 nW under a 0.9 V power supply at 27 oC. The estimated silicon area is 0.0012 mm2.

A self-biased current reference based on the MOSFET Zero Temperature Coefficient (ZTC) condition is presented. It can be implemented in any CMOS process and it provides a simple alternative to design a reference current suitable for low TC biasing. This topology was designed in a 0.18 μm process to generate 5 μA under a supply voltage from 1.4V to 1.8 V, spending a silicon area around 0.010mm2. From circuit simulations, the current reference is estimated to have a temperature coefficient (TCeff) of 15 ppm/°C from -40 to +85 °C and a fabrication sensitivity of σ/μ = 4.5%, including average process and local mismatch variability. The power supply sensitivity resulted around 1%V for this new reference.

This work presents a novel Switched-capacitor Bandgap Voltage Reference (SCBGR) circuit that dispenses entirely the use of resistors. The vEB negative drift and the thermal voltage (VT) positive drift voltages are both generated by the same PNP vertical bipolar transistor, avoiding diode mismatch problems. The current sources that are used to generate different junction current densities are averaged in the switching process, reducing their mismatch impact on the circuit performance. A switched-capacitor circuit stores and processes these voltages, generating the bandgap reference voltage after 5 clock cycles. Since capacitors are used instead of resistors, variability problems like average process spread and device mismatches are reduced. The proposed topology was designed and simulated in CMOS for 180 nm process. This paper presents a systematic comparison to the traditional dual-BJT BGR and demonstrates the better performance of this new topology with respect to the former. Monte Carlo simulation shows significantly lower spread resulting from variations in the output reference voltage and in its temperature coefficient (TC).

A novel resistorless bipolar junction transistor (BJT) bias and curvature compensation circuit for ultra-low-power CMOS bandgap voltage references (BGRs) is introduced. It works in the nanoampere current consumption range and under 1 V of power supply. The analytical behaviour of the circuit is described and simulation results for a 0.18 μm CMOS standard process are analysed. A junction voltage of 550 mV at room temperature is obtained (at an emitter current of 3.5 nA), presenting an almost linear temperature dependence, whereas the power consumption of the whole circuit is 3.4 nW under a 0.8 V power supply at 27°C. The estimated silicon area is 0.00135 mm 2 .

This paper presents a new approach for accurate M-2M MOSFET digital-to-analog converter (DAC) design. It describes a complete design methodology, where DAC inaccuracy is related to transistor geometry and bias through a powerful physics-based MOSFET mismatch model, very useful for hand design. Short-channel effects are also taken into account. Two versions of the converter were implemented in a 0.35 mum 3.3 V CMOS technology, and corroborate the theoretical development with statistical experimental results.

Component tolerances and mismatches due to process variations severely degrade the performance of bandgap reference (BGR) circuits. In this paper, the authors describe the design of a BGR considering the Pelgrom's mismatch model. The main purpose of our methodology is to convey the design to reach a good trade-off between area and mismatch. Implemented in standard 0.35mum CMOS technology, the circuit also includes a straightforward 4-bits trimming circuit to achieve more process variations independence. Its Monte Carlo temperature coefficient average is 40-ppm/degC and the reference output voltage average is 1.230V. The area of the BGR is 400x350mum2 due to our design matching requirements.