Current-controlled Oscillator Research Articles

A Process-Independent and Highly Linear DCO for Crowded Heterogeneous IoT Devices in 65-nm CMOS

The Internet of Things (IoT) devices are manufactured under different fabrication quality standards, considering the wide variety of vendors. As a result, global process variations in the IoT system-on-chip (SoC) are an enormous concern that can affect reliability of the device. Among the components in a typical SoC, oscillator is the most susceptible element to process variations. This paper proposes a feedback-assisted digitally controlled oscillator (DCO). The DCO has 512 operating modes, for wide-range frequency tuning from 0.6 to 3.1 GHz. By adding a dynamic feedback to inner current-controlled oscillator using a frequency-to-current converter, the DCO remains linear and invariant to the process for entire 2.5-GHz frequency band. Thanks to pseudodifferential cross-coupled structure used in each stage, this paper achieves a 2.3 ps deterministic jitter at 1.87-GHz output frequency. Furthermore, Monte Carlo analysis is performed at 1.87-GHz frequency; indicate that standard deviation from the mean is 2.47% that verifies reliability of this design. Power consumption varies from 0.86 to 3.68 mW at 1.2 V supply voltage, corresponding to the code word. The DCO is implemented in 65-nm standard CMOS process.

A Low-Noise Area-Efficient Chopped VCO-Based CTDSM for Sensor Applications in 40-nm CMOS

An area-efficient voltage-sensing readout circuit employing chopped voltage-controlled oscillator (VCO)-based continuous-time delta-sigma modulator (CTDSM) is presented in this paper. This VCO-based CTDSM features direct connection to sensors to eliminate pre-amplifier for achieving better hardware efficiency. The VCO is designed as a trans-conductor current-controlled oscillator, which is a fully differential $G_{m}$ stage cascaded with two CCOs, to provide a high-input impedance to sense the voltage signals from sensors. Analysis shows that the main noise and offset contributor is the $G_{m}$ stage. This problem is mitigated by employing choppers at critical location within the circuit. The VCO-based CTDSM is implemented in a 40-nm CMOS process. The power consumption is $17~\mu \text{W}$ under 1.2-V supply. With a 4-mVp (8-mV $_{\textrm {pp}})$ input, it achieves 61.85-dB signal-to-noise-and-distortion ratio over a 5-kHz bandwidth and the total harmonic distortion is −70.8 dB. The input-referred noise is 32 nV/ $\surd $ Hz. The chip area is only 0.0145 mm $^{\textrm {2}}$ .

A current-controlled oscillator with temperature, voltage, and process compensation

This paper presents a current-controlled oscillator (CCO) circuit design with temperature, voltage, and process compensation. A current reference biasing circuit comprising a complementary-to-absolute-temperature current and a proportional-to-absolute-temperature current is used for maintaining stability during temperature variations. In addition, an output current adjustment circuit is used to overcome process variation, and the voltage variation is compensated for by the connecting structure between the current reference and oscillator. The CCO was fabricated in a 0.18-μm CMOS process. The measured temperature variation coefficient is 48.8 ppm/°C across a temperature range of 0–100 °C, and the voltage variation coefficient is 0.13% for a supply voltage ranging from 1.62 to 1.98 V; overall power consumption is 64 μW.

A Wide Range CMOS Temperature Sensor With Process Variation Compensation for On-Chip Monitoring

A fully integrated temperature sensor along with a process compensator based on a frequency to voltage converter is presented in this paper. The proposed temperature sensor uses the difference between a reference current source and a proportional to absolute temperature current source to bias a differential ring-based current-controlled oscillator (CCO). The subtracted current in the CCO generates a linearized temperature-dependent frequency. To adjust the current sources and increase accuracy of the temperature sensor, a process compensator is added in the temperature sensor by adding switches to the architecture. With one point calibration, the maximum inaccuracy of ten measured samples is $-1.9~^{\circ }\text{C}\sim 1.5~^{\circ }\text{C}$ over a temperature range of −40 °C–100 °C. The total power consumption is $264~\mu \text{W}$ from a 1.5 V supply voltage at 25 °C. The temperature sensor is implemented in a standard 0.18- $\mu \text{m}$ CMOS process with an area of 0.0312 mm 2 .

A 0.2 V, 23 nW CMOS Temperature Sensor for Ultra-Low-Power IoT Applications

We propose a fully on-chip CMOS temperature sensor in which a sub-threshold (sub-VT) proportional-to-absolute-temperature (PTAT) current element starves a current-controlled oscillator (CCO). Sub-VT design enables ultra-low-power operation of this temperature sensor. However, such circuits are highly sensitive to process variations, thereby causing varying circuit currents from die to die. We propose a bit-weighted current mirror (BWCM) architecture to resist the effect of process-induced variation in the PTAT current. The analog core constituting the PTAT, the CCO, and the BWCM is operational down to 0.2 V supply voltage. A digital block operational at 0.5 V converts the temperature information into a digital code that can be processed and used by other components in a system-on-chip (SoC). The proposed temperature sensor system also supports resolution-power trade-off for Internet-of-things (IoT) applications with different sampling rates and energy needs. The system power consumption is 23 nW and the maximum temperature inaccuracy is +1.5/−1.7 °C from 0 °C to 100 °C with a two-point calibration. The temperature sensor system was designed in a 130 nm CMOS technology and its total area is 250 × 250 μm2.

Radio Frequency Tunable Oscillator Device Based on a SmB_{6} Microcrystal.

Radio frequency tunable oscillators are vital electronic components for signal generation, characterization, and processing. They are often constructed with a resonant circuit and a "negative" resistor, such as a Gunn diode, involving complex structure and large footprints. Here we report that a piece of SmB_{6}, 100 μm in size, works as a current-controlled oscillator in the 30MHz frequency range. SmB_{6} is a strongly correlated Kondo insulator that was recently found to have a robust surface state likely to be protected by the topology of its electronics structure. We exploit its nonlinear dynamics, and demonstrate large ac voltage outputs with frequencies from 20Hz to 30MHz by adjusting a small dc bias current. The behaviors of these oscillators agree well with a theoretical model describing the thermal and electronic dynamics of coupled surface and bulk states. With reduced crystal size we anticipate the device to work at higher frequencies, even in the THz regime. This type of oscillator might be realized in other materials with a metallic surface and a semiconducting bulk.

A low-power wide tuning-range CMOS current-controlled oscillator

This paper presents a low-power, small-size, wide tuning-range, and low supply voltage CMOS current-controlled oscillator (CCO) for current converter applications. The proposed oscillator is designed and fabricated in a standard 180-nm, single-poly, six-metal CMOS technology. Experimental results show that the oscillation frequency of the CCO is tunable from 30Hz to 970MHz by adjusting the control current in the range of 100fA to 10µA, giving an overall dynamic range of over 160dB. The operation of the circuit is nearly independent of the power supply voltage and the circuit operates at supply voltages as low as 800mV. Also, at this voltage, with control currents in the range of sub-nano-amperes, the power consumption is about 30nW. These features are promising in sensory and biomedical applications. The chip area is only 8.8×11.5µm2.

A Sub- $${100\,\hbox {ppm}/{^{\circ }\hbox {C}}}$$ 100 ppm / ∘ C Temperature-Compensated High-Frequency CMOS Relaxation Oscillator

A temperature-compensated high-frequency CMOS integrated relaxation oscillator with low frequency variations is presented. A current-controlled oscillator topology is employed with a resistive source-degenerated transconductor and a current comparator to achieve high oscillation frequency and low power dissipation. The proposed oscillator was designed with process parameters from a standard 0.35-$$\upmu $$μm CMOS technology and a 2.5-V single power supply voltage. At a nominal oscillation frequency of 21 MHz, the total power dissipation of the circuit was 201 $$\upmu $$μW. Post-layout simulation results showed that the frequency variations were less than $${34.16\,\hbox {ppm}/{^{\circ }\hbox {C}}}$$34.16ppm/?C over a temperature range of $$-40$$-40 to $$+120\,^{\circ }\hbox {C}$$+120?C.

Bridge Resistance Deviation-to-Period Converter for Resistive Biosensors

A bridge resistance deviation-to-period (BRD-to-P) converter is presented for interfacing resistive biosensors. It consists of a linear operational transconductance amplifier (OTA) and a current-controlled oscillator (CCO) formed by a current-tunable Schmitt trigger and an integrator. The free running period of the converter is 1.824 ms when the bridge offset resistance is 1 kΩ. The conversion sensitivity of the converter amounts to 3.814 ms/Ω over the resistance deviation range of 0-1.2 Ω. The linearity error of the conversion characteristic is less than ±0.004 %.

Multisensor readout circuit using a multiple differential-input operation amplifier with pulse output

In this paper, a CMOS multisensor readout circuit is presented. A multiple differential-input operational amplifier (MDI-OPA) with three distinct positive inputs and one common negative input is designed to make one of the three inputs to act as a general differential-input OPA through a built-in multiplexer. A voltage-to-current converter and a current-controlled oscillator are integrated with the MDI-OPA so that the selected analog input voltage can be used to generate a pulse output whose frequency is linearly proportional to the selected input voltage. The linearity of the transfer characteristic is at least 99.99% for input voltages below 1.44 V. An added current-offset structure is used to modify the transfer characteristic that usually varies owing to process variation. The measured output transfer characteristics of three input channels show nearly the same sensitivity of 90 Hz/mV or so with a linearity of at least 99.99% with the assistance of the current-offset mechanism.

CMOS temperature sensor using a resistively degenerated common-source amplifier biased by an adjustable proportional-to-absolute-temperature voltage

A high-linearity CMOS temperature sensor with pulse output is presented. The temperature core is a resistively degenerated common-source amplifier which gate is biased by a proportional-to-absolute-temperature (PTAT) voltage generator. The source resistor is made of polysilicon which resistance has a PTAT characteristic. The current flowing through the resistor exhibits a PTAT characteristic with high linearity of 99.99% at least for a temperature range from 0 to 125 °C. The PTAT voltage generator can be adjusted by a bias voltage Vb and hence the PTAT current can also be adjusted by the Vb. The PTAT current is mirrored to an added current controlled oscillator which output pulse frequencies also exhibit a PTAT characteristic. For the chip using the 0.35 µm process, the plots of measured pulse frequencies against temperature exhibit the sensitivity of 2.30 to 2.24 kHz/°C with linearity of more than 99.99% at the Vb of 1 to 1.2 V.

Monolithic CMOS ISFET with Built-in Gold Reference Electrode and Readout Circuit with Frequency-adjustable Pulse Output in Bio Detection

ISFET with built-in gold reference electrode and integrated readout circuits with frequency-adjustable pulse output is presented. Sensing membrane is surrounded by gold electrodes, treated as reference electrode and working electrode separately, can be as chemical or bio-molecule detection sensor. The ISFET is one of the input differential transistor pair of an operational amplifier in its readout circuit, which mainly consists of a voltage-to-current converter and a current-controlled oscillator. The output pulse frequency is linearly proportional to the effective gate voltage of the ISFET, which is immersed in the analyzed solution with a stably biasing reference electrode. A current-offset structure is added into the oscillator to shift the transfer characteristic line of the output frequency versus the effective input voltage. The transfer characteristics of the pulse frequency versus pH value are measured by an external Ag/AgCl reference electrode and a built-in gold reference electrode, respectively.

A Self-Oscillating System to Measure the Conductivity and the Permittivity of Liquids within a Single Triangular Signal

We present a methodology and a circuit to extract liquid resistance and capacitance simultaneously from the same output signal using interdigitated sensing electrodes. The principle consists in the generation of a current square wave and its application to the sensor to create a triangular output voltage which contains both the conductivity and permittivity parameters in a single periodic segment. This concept extends the Triangular Waveform Voltage (TWV) signal generation technique and is implemented by a system which consists in a closed-loop current-controlled oscillator and only requires DC power to operate. The system interface is portable and only a small number of electrical components are used to generate the expected signal. Conductivities of saline NaCl and KCl solutions, being first calibrated by commercial equipment, are characterized by a system prototype. The results show excellent linearity and prove the repeatability of the measurements. Experiments on water-glycerol mixtures validate the proposed sensing approach to measure the permittivity and the conductivity simultaneously. We discussed and identified the sources of measurement errors as circuit parasitic capacitances, switching clock feedthrough, charge injection, bandwidth, and control-current quality.

Micro-TEG Voltage Supplies for Spin Torque Oscillators

Spin torque oscillators (STOs) can be viewed as current-controlled oscillators. Oscillations start if the current exceeds some critical value-threshold current. A low critical current is required to achieve a high output power. Recently, the critical current was reduced to as low as 0.1 mA and STO majority gate was proposed. To operate STO logic, an mV-level voltage source with output current greater than the critical current (0.1 mA), and very low impedance is needed. This paper proposes power supplies that use microthermoelectric generators (μTEGs) to convert heat into electric power. A complete analytical μTEG model was developed that includes all the relevant physical effects. This model is used to predict power and perform geometry optimization to maximize thermal energy conversion. We propose metallic thermocouples to realize the low impedance source and connect them electrically in parallel to deliver sufficient current. The proposed μTEG consists of four thermocouples connected in parallel both thermally and electrically. Thermo-legs are homogeneous and thermally isolated with a thermal isolation cavity to minimize heat leakage. Simulations with a 30-K temperature drop across μTEGs showed that the proposed structure can potentially integrate ~ 50 000 μTEGs/cm2 and efficiently harvest heat to supply new STO logic.

Detector of abrupt current variations on power lines

A system to detect abrupt current variations occurring on high-powered conductors (> 10 A) is proposed. The detection system is composed of an inductive transducer interfaced by a saw-tooth current-controlled oscillator (CCO). The transducer consists of a spiral highpass inductor, the role of which is to catch the magnetic flux induced by the current generated on the power line, the sensor being connected to the source branch of the CCO control current. Each magnetic perturbation is therefore transformed into an induced current added to the CCO source current, thus deforming the output transient saw-tooth voltage of the circuit. The authors have defined an output characteristic based on the measurement of each period of the oscillating voltage; the information is consequently extracted from the comparison of the measured periods with the natural oscillating period of the CCO. The system has been implemented on a printed circuit board, tested for the arc fault detection application and compared with a Hall reference probe. The proposed measuring method allowed discriminating the arcing occurrences from the normal operation of the power conductors in three different regimes: i.e. when the power line is loaded by an open circuit, a resistive load, or an electrical motor. © 2013 Institution of Engineering and Technology.

Current-mode phase-locked loop with constant-Q active inductor CCO and active transformer loop filter

This paper presents a current-mode phase-locked loop (PLL) with a constant-Q CMOS active inductor current-controlled oscillator (CCO) and a CMOS current-mode active-transformer loop filter. The constant-Q active inductor provides a large and swing-independent quality factor such that the phase noise of the CCO utilizing the constant-Q active inductor is comparable to that of CCO with spiral inductors. The current-mode active-transformer loop filter offers the advantage of a large and tunable inductance and low silicon consumption such that the loop bandwidth of the PLL can be made small and tunable. The PLL was designed in TSMC-0.18 μm 6-metal 1.8V CMOS technology and analyzed using SpectreRF from Cadence Design Systems with BSIM3v3 device models. The phase noise of the PLL was analyzed using Cadence's Verilog-AMS behavioral modeling. The phase noise of the CCO with the constant-Q active inductor is ?123.1 dBc/Hz at 1 MHz frequency offset, over 10 dB better as compared with that of the CCO with conventional active inductors, and is only a few dB higher than that of the CCO with spiral inductors. The phase noise of the PLL with an active-transformer loop filter and a constant-Q CCO is ?116 dBc/Hz at 1 MHz frequency offset, nearly 20 dB lower than that of the PLL with the same active-transformer loop filter and a conventional active-inductor CCO. The lock time, power consumption, and phase noise of the PLL are 60 ns, 34 mW, and ?116 dBc/Hz at 1 MHz frequency offset, respectively. The total silicon consumption of the PLL excluding bond pads is 0.013 mm2.

A new CMOS current controlled oscillator with minimum phase noise based on a low parasitic resistance CCII

In this paper we present a design of a minimum phase noise current controlled oscillator in CMOS technology. Owing to their high degree of controllability, the second generation current conveyer is used as a basic block for our oscillator. Thus, the first step in our design was to improve static and dynamic behaviour of second generation current conveyers. We present therefore a design of CMOS class AB second generation current conveyors. The translinear implementation in CMOS technology was first studied and then a considerable improvement of the parasitic series resistance on port X is done by presenting a structure of CCII. With a control current of 300 µA, a reduction of RX by a factor of 10 is observed leading to a notable improvement of the frequency behaviour. This improved CCII version was used as a basic building block in the design of a new current controlled oscillator covering [100MHz-600MHz] frequency is presented. Phase noise characteristics of the presented oscillator are investigated. We present then a new methodology of modelling and optimisation of phase noise of current controlled oscillators for CMOS process. This optimization strategy leads to a minimum phase noise acting on device geometries and design sources. PSpice simulation results are performed using CMOS 0.35 µm process of AMS.

A Fully-Integrated, Short-Range, Low Data Rate FM-UWB Transmitter in 90 nm CMOS

This paper presents a fully-integrated 3-5 GHz-band FM-UWB transmitter implemented in 90 nm bulk CMOS. The front-end consists of an RF current-controlled oscillator (RF-ICO) and class-AB power amplifier. Transmit data modulates a sub-carrier oscillator. The 2-FSK modulated output is amplified by a transconductor, and directly modulates the RF-ICO tune input. A successive approximation register (SAR) algorithm and on-chip all-digital frequency-locked loop (FLL) calibrate the carrier and sub-carrier frequencies. All voltage and current references required by the transmitter are included on-chip. The 0.2 × 0.5 mm2 active area transmitter consumes 900 μW from a 1 V supply. Energy efficiency of the transmitter is 9 nJ/bit running continuously at 100 kbits/s.

A CMOS CURRENT CONTROLLED RING OSCILLATOR WITH WIDE AND LINEAR TUNING RANGE

A new CMOS current controlled ring oscillator is investigated. It is based on a 3 stage ring oscillator. Each stage uses a simple NMOS for switching a current source to charge a capacitor and discharging it thereby generating a ramp output. Its oscillation frequency depends on the current source. This simple circuit can have a wide tuning range but has some non-linearity problem. A modification of the original circuit using inverters can significantly improve the linearity without consuming a lot of additional current and layout. Simulation result using 1pF indicates that the oscillator has 476KHz/uA frequency sensitivity and can be tuned from 476Hz at 1nA to 476KHz at 1000nA with good linearity.

Vortex Nucleation Phase in Spin Torque Oscillators Based on Nanocontacts

We study the starting up phase of a current-controlled oscillator based on a magnetic vortex orbiting around a nanocontact in a spin-valve. From the idle state, current pulses down to a few nanoseconds can create the vortex, which is detected through the electrical signature of its steady-state gyration. Two ns are needed to reach the in-current equilibrium. The process can then be described by an Arrhenius law, with an activation energy that is consistent with the Oersted-field-induced separation of a vortex-antivortex pair. Requirements for deterministic nucleation are deduced, with prospects for instant-on oscillator capability.