Current-Mode High-Accuracy High-Precision CMOS Amplifiers

In low-voltage, deep sub- mum analog CMOS circuits, the accuracy and precision can be limited by the finite gain as well as by the input offset and 1/f noise voltages of opamps. Here, we show how to design high-accuracy high-precision CMOS amplifiers by properly applying dynamic element matching to a second-generation current conveyor (CCII); if all of the critical, nominally identical transistor pairs are dynamically matched, the resulting amplifier has low residual input offset and noise voltages. When compared with chopper or traditional dynamic element-matching amplifiers, the proposed approach alleviates the tradeoff between output swing and output resistance and is more robust against the finite opamp gain. Transistor-level simulations confirm theoretical results.     

A 1-V BiCMOS rail-to-rail amplifier with n-channel depletion modeinput stage

A BiCMOS rail-to-rail operational amplifier capable of operating from supply voltages as low as 1 V is presented. The folded cascode input stage uses an nMOS depletion mode differential pair to provide rail-to-rail common mode voltage range while typically requiring only 40 fA of input bias current. The bipolar transistor differential-to-single-ended conversion network employs a low-voltage base current cancellation technique which provides high input stage voltage gain from a l-V supply yet allows a 3-V/μs slew rate capability. The bipolar transistor output stage uses a low-voltage translinear loop which maintains a low impedance signal path to the output common emitter power devices. This circuit topology enables the amplifier to achieve a 4-MHz bandwidth with 60° of phase margin. The output voltage can swing to within 50 mV of each supply rail. An “on-demand” base current boost technique will be presented which can provide up to 50 mA of output drive capability from a 5-V supply, yet consumes only a few microamps when the output is in the quiescent state. A low voltage level shift technique will be described which uses an n-channel depletion mode source follower to provide isolation between the input and output stages     

Ultra low-voltage CMOS current mirrors

In this paper we present an ultra low-voltage bidirectional and continuous time current mirror based on clocked semi-floating-gate transistors. The current mirror may be used with supply voltages down to 250 mV and frequencies up to several hundred MHz. The simulated data presented are obtained using the Spectre simulator provided by Cadence and valid for a 90 nm TSMC CMOS process.     

A Wired-AND Current-Mode Logic Circuit Technique in CMOS for Low-Voltage, High-Speed and Mixed-Signal VLSIC

A wired-AND current-mode logic (WCML) circuit techniquein CMOS technology for low-voltage and high-speed VLSI circuitsis proposed, and a WCML cell library is developed using standard0.8 micron CMOS process. The proposed WCML technique appliesthe analog circuit design methodologies to the digital circuitdesign. The input and output logic signals are represented bycurrent quantities. The supply current of the logic circuitis adjustable for the required logic speed and the switchingnoise level. The noise is reduced on the power supply lines andin the substrate by the current-steering technique and by thesmooth swing of the reduced node potentials. Precise analogcircuits and fast digital circuits can be integrated on the samesilicon substrate by using the low noise property of the WCML.It is shown by the simulations that at low supply voltages, theWCML is faster and generates less switching noise when comparedto the static-CMOS logic. At high speeds, the power dissipationof the WCML is less than that of the static-CMOS logic.     

A 1-V, 8-bit successive approximation ADC in standard CMOS process

A 1-V 8-bit 50-kS/s successive approximation analog-to-digital converter (ADC) implemented in a conventional 1.2-μm CMOS process is presented. Low voltage, large signal swing sample-and-hold, and digital-to-analog conversion are realized based on inverting op-amp configurations with biasing currents added to the op-amp negative input terminal so that the op-amp input common-mode voltages can be biased near ground to minimize the supply voltage. At the same time, the input and output quiescent voltages can be set at half of the supply rails. A low-voltage latched comparator is realized based on the current-mode approach. The entire ADC including all the digital circuits consumes less than 0.34 mW. An effective number of bits of 7.9 was obtained for a 1-kHz 850-mV peak-to-peak input signal     

A 1.5-V current-mode CMOS sample-and-hold IC with 57-dB S/N at 20MS/s and 54-dB S/N at 30 MS/s

A new video-speed current-mode CMOS sample-and-hold IC has been developed. It operates with a supply voltage as low as 1.5 V, a signal-to-noise ratio (S/N) of 57 dB and 54 dB with a 1-MHz input signal at clock frequencies of 20 and 30 MHz, and a power dissipation of 2.3 mW. It consists of current-mirror circuits with the node voltages at the input and the output terminals which are kept constant in all phases of the input signal by the use of low-voltage operational amplifiers; this reduces the signal current dependency. The low-voltage operational amplifier consists of a MOS transistor and a constant current source in a common-gate amplifier configuration. Only two analog switches in differential form were used to construct the differential sample-and-hold circuit. This minimizes the error caused by the switch feed through, and thus high accuracy can be realized. Since there is no analog switch in the input path, it is possible to convert the input signal voltage to a current by simply connecting an external resistor. The circuit was fabricated using standard 0.6-μm MOS devices with normal threshold voltages (V_th) of +0.7 V (nMOS) and -0.7 V (pMOS)     

250 mV Supply Voltage Digital Low‐Dropout Regulator Using Fast Current Tracking Scheme

This paper proposes a 250 mV supply voltage digital low‐dropout (LDO) regulator. The proposed LDO regulator reduces the supply voltage to 250 mV by implementing with all digital circuits in a 0.11 μm CMOS process. The fast current tracking scheme achieves the fast settling time of the output voltage by eliminating the ringing problem. The over‐voltage and under‐voltage detection circuits decrease the overshoot and undershoot voltages by changing the switch array current rapidly. The switch bias circuit reduces the size of the current switch array to 1/3, which applies a forward body bias voltage at low supply voltage. The fabricated LDO regulator worked at 0.25 V to 1.2 V supply voltage. It achieved 250 mV supply voltage and 220 mV output voltage with 99.5% current efficiency and 8 mV ripple voltage at 20 μA to 200 μA load current.     

1-V operational amplifier with rail-to-rail input and output ranges

A bipolar operational amplifier (OA) with rail-to-rail input and output ranges which can operate at supply voltages down to 1 V is presented. At this supply voltage, the input offset voltage is typically 1.0 mV in an input common-mode voltage range that extends beyond both supply rails for about 300 mV, with a common-mode rejection ratio (CMRR) between 38 and 100 dB, depending on conditions. The output voltage can reach both supply rails within 100 mV, the output current is limited to ±10 mA, the voltage gain is 100 dB, and the bandwidth is 450 kHz. The die is 2.5×5.5 mm². Qualities such as offset, input-bias current, and CMRR are improved when the supply voltage is increased and the dynamic level shift is autonomically turned off. The OA has been protected against unintentional reversal of the output signal when the inputs are substantially overdriven. The output stage of the circuit consists of two full complementary composite transistors, whose HF characteristics have been improved by internal Miller compensation and linearization of the transconductance     

A novel class of complementary folded-cascode opamps for low voltage

Three novel complementary folded-cascode operational amplifiers (opamps) with high gain, large bandwidth, and rail-to-rail input range for low-voltage operation will be presented. These opamps feature high bandwidth due to minimum internal nodes. The output swing is increased by properly adjusting the output cascode transistor gate voltages close to the power supply voltages. The opamps have been fabricated with a standard 0.8-/spl mu/m CMOS technology. Measurements show the amplification is between 60.1 and 72.4 dB, and the unity gain bandwidth is 14 MHz for a 5-pF load, 2.5-V power supply, and 150-/spl mu/A bias current.     

A Low-Voltage Fully Differential Constant-Gm Rail-to-Rail CMOS Operational Amplifier

A low-voltage fully differential CMOS operational amplifier withconstant-g_mand rail-to-rail input and output stages ispresented. It is the fully differential version of a previously realizedsingle-ended operational amplifier where a novel circuit to ensure constanttransconductance has been implemented [1]. The input stage is a rail-to-railstructure formed by two symmetrical OTAs in parallel (the input transistorsare operating in weak inversion). The class-AB output stages have also afull voltage swing. A rail-to-rail input common mode feedback structureallows the output voltage control. Measurements in a 0.7 µ standardCMOS process with threshold voltages of about 0.7 V have been done. Theminimum experimental supply voltage is about 1.1 V. The circuit provides a60 dB low frequency voltage gain and about 1.5 MHz unity gain frequency fora total power consumption of about 0.72 mW at a 1.5 V supply voltage.     

Design of low-voltage CMOS continuous-time filter with on-chipautomatic tuning

A technique for designing a low-voltage continuous-time active filter is presented in this paper. In this technique, current sources are added to the inverting or noninverting op-amp terminals such that the op-amp input common-mode voltages can be set close to one of the supply rails to allow low-voltage operation. An automatic frequency and Q tuning technique is proposed for tuning the active filter using programmable capacitor arrays (PCAs). The proposed tuning technique does not require any peak detectors, which are difficult to implement at a low supply voltage. Instead, it uses a few analog comparators, a digital comparator, and a few binary counters to adjust the PCAs. To demonstrate the proposed techniques, a 1-V 1-MHz second-order filter fabricated in a conventional 1.2-μm CMOS process is presented. For a 5-kHz input signal, the filter achieves a THD of -60.2 dB for a peak-to-peak output voltage of 600 mV. The frequency tuning range is between 585 kHz and 1.325 MHz. The measured power consumption for the filter alone consumes about 0.52 mW and for the entire system consumes about 1.6 mW for a supply voltage of ±0.5 V     

A 65 nm Sub-$V_{t}$ Microcontroller With Integrated SRAM and Switched Capacitor DC-DC Converter

Aggressive supply voltage scaling to below the device threshold voltage provides significant energy and leakage power reduction in logic and SRAM circuits. Consequently, it is a compelling strategy for energy-constrained systems with relaxed performance requirements. However, effects of process variation become more prominent at low voltages, particularly in deeply scaled technologies. This paper presents a 65 nm system-on-a-chip which demonstrates techniques to mitigate variation, enabling sub-threshold operation down to 300 mV. A 16-bit microcontroller core is designed with a custom sub-threshold cell library and timing methodology to address output voltage failures and propagation delays in logic gates. A 128 kb SRAM employs an 8 T bit-cell to ensure read stability, and peripheral assist circuitry to allow sub-Vt reading and writing. The logic and SRAM function in the range of 300 mV to 600 mV, consume 27.2 pJ/cycle at the optimal V _DD of 500 mV, and 1 muW standby power at 300 mV. To supply variable voltages at these low power levels, a switched capacitor DC-DC converter is integrated on-chip and achieves above 75% efficiency while delivering between 10 muW to 250 muW of load power.     

Scalable Bang–Bang Phase-Locked-Loop-based integrated sensor interfaces

The scaling of VLSI technology results in reduced supply voltages, hence jeopardizing the voltage swing and signal-to-noise ratio achievable by analog integrated circuits. An alternative is to take advantage of the increased timing resolution of faster CMOS technologies, and to replace traditional voltage-mode processing by time-based circuits. Time-based design enables us to implement highly-digital sensor interfaces, which can benefit from scaling in terms of area reduction, compared to analog implementations. In addition, it enables low-voltage and low-power design. This invited overview paper gives a survey of one type of such time-based sensor interfaces: the Bang–Bang Phase-Locked-Loop-based Sensor-to-Digital Converter. The highly-digital implementation of the frequency-based sensor interface results in low-voltage, low-power, robust and highly-scalable designs. Several design examples are elaborated, each focusing on a different design aspect.     

Operational amplifier with 1-V rail-to-rail multipath-driven outputstage

A bipolar operational amplifier (op amp) with a rail-to-rail multipath-driven output stage that operates at supply voltages down to 1 V is presented. The bandwidth of this output stage is as high as possible, viz, equal to that of one of the output transistors, loaded by the output capacitance. The output voltage can reach both supply rails within 100 mV and the output current is ±15 mA. The op amp is designed to be loaded by a 100-pF capacitor and the unity-gain bandwidth is 3.4 MHz at a 60° phase margin. The voltage gain is 117 dB and the CMRR is 100 dB. The frequency behavior of the multipath-driven (MPD) topology has an improved performance when compared to that of previously presented low-voltage output stages. A figure of merit F_M for low-voltage op amps has been defined as the bandwidth-power ratio     

A realization of a below-1-V operational and 30-MS/s sample-and-hold IC with a 56-dB signal-to-noise ratio by applying the current-based circuit approach

This paper demonstrates the low-voltage and low-power operation of a MOS sample-and-hold circuit while preserving speed and accuracy, aiming at the realization of a pipelined low-voltage and low-power analog-to-digital converter on a system large-scale integrated circuit. It was fabricated by utilizing 0.35-/spl mu/m CMOS technology. The main feature of this circuit is that all the input, signals, and output are in the current form. The circuit consists of simple current mirrors. In order to eliminate the signal-dependent current transfer ratio error, voltages at the drain terminals of mirror transistors are fixed as constant. A source degeneration resistor, which is a transistor in the triode operational region, is connected to a mirror transistor in order to alleviate the influence of the threshold and transconductance parameter variations. Control signals are boosted in voltage and applied to the gate of switch NMOS transistors in the signal path in order to reduce the on-resistance of analog switches. A differential configuration is adopted throughout the entire circuit and effectively cancels switch feedthrough errors. As a result, a 30-MS/s operation with a signal-to-noise ratio (SNR) of 56 dB from a 1-V supply has been achieved, when the input current is /spl plusmn/200 /spl mu/A. The chip even operated down to 0.85 V with a 20-MHz clock. The SNR was measured as 50 dB with an input current of /spl plusmn/100 /spl mu/A.     

Ultra Low-Voltage Floating-Gate (FGUVMOS) Amplifiers

This paper presents an approach to programming threshold voltages in floating-gate CMOS circuits. The threshold voltage programming is exploited in ultra low-voltage (ULV) amplifier design. A threshold voltage programming scheme is presented and several examples of analog ULV circuits are described. The ULV circuits are used in ULV amplifier design. Measured data are provided.     

一种基于准浮栅技术的折叠差分结构及其应用

提出了一种基于准浮栅技术的新型折叠差分结构,其偏置电流源的电压降被折叠到输出电压摆幅中,且不受共模输入电压限制而达到较大范围,非常适于低压应用。基于此结构,实现了一种超低压运算放大器。仿真分析表明,该运算放大器能够实现轨到轨(rail-to-rail)的共模输入电压范围和输出电压摆幅,以及较高的共模抑制比。     

适用于ASIC的高速低功耗逻辑单元

本文介绍一种ECL电路结构形式的ASIC逻辑单元的设计和应用。该单元使用2.5V的电源,内部开关电流设计为0.5mA,逻辑摆幅设计为340mV,输入输出均采用双向互补信号。它具有信息的基本记忆功能,用它进行多级组合配套设计,可制作不同模数的分频器、寄存器和计数器等。设计灵活,功能强,电路速度快,功耗低,仅为具有相同功能的普通ECL电路的1/30。这些电路可用在通讯机、电子控制系统、电子测量系结中作高速数字锁相环,数字信号处理的专用集成电路。     

A low-voltage,versatile CMOS four-quadrant analogue multiplier

This paper describes a four-quadrant analogue multiplier circuit using a low-voltage power supply. It comprises two voltage/current adders and a basic multiplier. Its major advantages over other low-voltage multipliers are that it can operate on either a single power supply or two power supplies, and that its output can be the product of two signal currents, the product of two signal voltages, or the product of a signal current and a signal voltage. Second-order effects were analysed and the simulated results revealed that: (1) for a two-power supply voltage of 2?V, the total harmonic distortion is about 1%, whereas the input voltage is 0.4?V_P–P, the power dissipation is about 0.4?mW and the ?3?dB bandwidth is more than 55?MHz; (2) for a single-power supply voltage of 2?V, the total harmonic distortion is about 1%, whereas the input voltage is 0.4?V_P–P, the power dissipation is about 0.2?mW and the ?3?dB bandwidth is more than 55?MHz. Experimental results are provided to confirm the operation of the circuit.     

Low-voltage FGMOS based analog building blocks

Novel floating gate MOSFET (FGMOS) based low-voltage analog circuits such as current-to-voltage converter, current-mode divider and pseudo-exponential function generator are proposed in this paper. The inherent advantages of these circuits are their simplicity, accuracy and low power dissipation. The current-to-voltage converter is operated with a single power supply of 0.9 V. The current-mode divider and pseudo-exponential function generator are operated at supply voltages of ±0.9 V. It was observed that the power dissipation of the current-to-voltage converter is reduced to 12 μW using a single power supply. The power dissipations of the current-mode divider and pseudo-exponential function generator are found to be 356 and 471 μW, respectively. The proposed circuits are simulated using SPICE in 0.5 μm CMOS process technology to demonstrate the feasibility and the effectiveness of the proposed circuits.