Source Follower Circuit Research Articles

A Low Mismatch Current Charge Pump Applied to Phase-Locked Loops.

This paper presents a charge pump circuit with a wide output range and low current mismatch applied to phase-locked loops. In this designed structure, T-shaped analog switches are adopted to suppress the non-ideal effects of clock feedthrough, switching time mismatch, and charge injection. A source follower and current splitting circuits are proposed to improve the matching accuracy of the charging and discharging currents and reduce the current mismatch rate. A rail-to-rail high-gain amplifier with a negative feedback connection is introduced to suppress the charge-sharing effect of the charge pump. A cascode current mirror with a high output impedance is used to provide the charge and discharge currents for the charge pump, which not only improves the current accuracy of the charge pump but also increases the output voltage range. The proposed charge pump is designed and simulated based on a 65 nm CMOS process. The results show that when the power supply voltage is 1.2 V, the output current of the charge pump is 100 μA, the output voltage is in the range of 0.2~1 V, and the maximum current mismatch rate and current variation rate are only 0.21% and 1.4%, respectively.

A VCO-Based ADC With Direct Connection to a Microphone MEMS, 80-dB Peak SNDR and 438-μW Power Consumption

This article presents a microphone readout chip incorporating a voltage controlled oscillator (VCO)-based ADC that can be directly connected to a capacitive micro electro mechanical systems (MEMSs) sensor without requiring a voltage buffer. The ADC uses an open-loop pseudo-differential architecture with two ring oscillators followed by a coarse–fine frequency-to-digital converter. The proposed coarse–fine architecture optimizes power consumption, thanks to a new algorithm. The MEMS is connected to the ring oscillators with a source follower circuit that can be programed to interchange signal to noise ratio (SNR) by the power consumption in small steps. This feature enables always-on operation in voice recognition applications. The microphone is compatible with standard PDM audio interfaces. Total ADC power consumption ranges between 245 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$438 \mu \text{W}$ </tex-math></inline-formula> for peak signal-to-noise and distortion ratios (SNDRs) between 74 and 80.3 dB-A, including the ADC and MEMS coupling circuitry. The dynamic range (DR) achieves 108 dB at full performance with a total harmonic distortion (THD) of 1.5% at the acoustic overload point (AOP) of 128 dBSPL. The ADC occupies an area of 0.14 mm2 implemented in 0.13- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS.

Design of LDO circuit based on curvature compensation reference closed-loop stability

In this paper, a low dropout (LDO) circuit based on a curvature compensation benchmark and closed-loop stability is designed. This circuit compensates for the higher order term of VBE in a BJT through the subthreshold characteristic of MOSFET and achieves the effect of curvature compensation. The bandgap reference circuit provides a stable input voltage for the LDO circuit, while the source follower and adaptive bias circuit improve the response speed and closed-loop stability of the LDO circuit. The temperature drift coefficient of the bandgap circuit is 8.11 ppm/°C, the input voltage is 3–5 V, the output voltage is 2.8 V, and the linear adjustment rate is 0.22%.

A Smart Floating Gate Transistor with Two Control Gates for Active Noise Control.

A smart floating gate transistor with two control gates was proposed for active noise control in bioelectrical signal measurement. The device, which is low cost and capable of large-scale integration, was implemented in a standard single-poly complementary metal–oxide–semiconductor (CMOS) process. A model of the device was developed to demonstrate the working principle. Theoretical analysis and simulation results proved the superposition of the two control gates. A series of test experiments were carried out and the results showed that the device was in accordance with the basic electrical characteristics of a floating gate transistor, including the current–voltage (I–V) characteristics and the threshold characteristics observed on the two control gates. Based on the source follower circuit, the experimental results proved that the device can reduce interference by more than 29 dB, which demonstrates the feasibility of the proposed device for active noise control.

Optical-Interferometry-Based CMOS-MEMS Sensor Transduced by Stress-Induced Nanomechanical Deflection.

We developed a Fabry–Perot interferometer sensor with a metal-oxide-semiconductor field-effect transistor (MOSFET) circuit for chemical sensing. The novel signal transducing technique was performed in three steps: mechanical deflection, transmittance change, and photocurrent change. A small readout photocurrent was processed by an integrated source follower circuit. The movable film of the sensor was a 350-nm-thick polychloro-para-xylylene membrane with a diameter of 100 µm and an air gap of 300 nm. The linearity of the integrated source follower circuit was obtained. We demonstrated a gas response using 80-ppm ethanol detected by small membrane deformation of 50 nm, which resulted in an output-voltage change with the proposed high-efficiency transduction.

Improvements of low-detection-limit filter-free fluorescence sensor developed by charge accumulation operation

We developed a low-detection-limit filter-free fluorescence sensor by a charge accumulation technique. For charge accumulation, a floating diffusion amplifier (FDA), which included a floating diffusion capacitor, a transfer gate, and a source follower circuit, was used. To integrate CMOS circuits with the filter-free fluorescence sensor, we adopted a triple-well process to isolate transistors from the sensor on a single chip. We detected 0.1 nW fluorescence under the illumination of excitation light by 1.5 ms accumulation, which was one order of magnitude greater than that of a previous current detection sensor.

Analog and RF performance of a multigate FinFET at nano scale

In this paper, analog and RF performance of the Fin field effect transistor (FET) at Nano scale is observed through 3D simulation. FinFET devices like rectangular gate all around (RE-GAA) FinFET, cylindrical gate all around (CY-GAA) FinFET and triple gate (TG) FinFET are observed. The figure of merit (FOMs) such as input-output characteristics, trans-conductance (gm), output-conductance (gd), intrinsic gain (gm/gd), gate capacitance (gate to source and total gate capacitance), unity gain cut-off frequency (ft), trans-conductance generation factor (TGF), gain frequency product (GFP), gain bandwidth product (GBP) and gain transconductance frequency product (GTFP) are observed. The analog performance of a FinFETs are observed by realising source follower circuit with NMOS transistor as a current source. The source follower circuit gain is observed. It has been observed that maximum capacitance is observed in case gate all around condition. Rectangular gate all around has the highest transconductance. In the source follower circuit, the gain curve (Vout/Vin) is sharper for TG-FinFET.

P‐51: A Novel Analog Buffer Circuit using Low Temperature Poly‐Si TFT

AbstractA novel source follower circuit employing low temperature polycrystalline silicon (LTPS) thin film transistors (TFT) is proposed as an analog buffer for integrated data driver circuit. Instead of capacitive bootstrapping for self‐compensation of the characteristic of TFTs, a new compensation method is applied so that the error programming of gate voltage of driving TFT can be effectively eliminated. The feasibility of proposed circuit is exhibited through the simulation results.

Design and Implementation of A CMOS Light Pulse Receiver Cell Array for Spatial Optical Communications

A CMOS light pulse receiver (LPR) cell for spatial optical communications is designed and evaluated by device simulations and a prototype chip implementation. The LPR cell consists of a pinned photodiode and four transistors. It works under sub-threshold region of a MOS transistor and the source terminal voltage which responds to the logarithm of the photo current are read out with a source follower circuit. For finding the position of the light spot on the focal plane, an image pixel array is embedded on the same plane of the LPR cell array. A prototype chip with 640 × 240 image pixels and 640 × 240 LPR cells is implemented with 0.18 μm CMOS technology. A proposed model of the transient response of the LPR cell agrees with the result of the device simulations and measurements. Both imaging at 60 fps and optical communication at the carrier frequency of 1 MHz are successfully performed. The measured signal amplitude and the calculation results of photocurrents show that the spatial optical communication up to 100 m is feasible using a 10 × 10 LED array.

Charge Accumulation Type Hydrogen Ion Image Sensor with High pH Resolution

We propose a charge transfer type ion image sensor operated using a charge accumulation technique that accumulates the output signal and integrates it temporally. This technique is expected to image hydrogen ion distributions with a high signal-to-noise (S/N) ratio. The sensor was fabricated using large-scale integration technology, so that its size was very compact, and its specialized charge transfer characteristics allowed it to amplify the signal without any external amplification. The sensor noise was independent of the sensing area size, and the noise power was determined by the noise of the source follower circuit. In 5 accumulation cycles, the S/N ratio increased by √5 times and the pH-referred noise, which indicates the pH sensor resolution, was reduced from 0.09 to 0.06 pH. The sensor effectively obtained a real-time image of the hydrogen ion distribution in a solution with a resolution of pH 0.1, which would not be possible without charge accumulation.

Design and Construction of a Cost Effective Headstage for Simultaneous Neural Stimulation and Recording in the Water Maze

Headstage preamplifiers and source followers are commonly used to study neural activity in behavioral neurophysiology experiments. Available commercial products are often expensive, not easily customized, and not submersible. Here we describe a method to design and build a customized, integrated circuit headstage for simultaneous 4-channel neural recording and 2-channel simulation in awake, behaving animals. The headstage is designed using a free, commercially available CAD-type design package, and can be modified easily to accommodate different scales (e.g. to add channels). A customized printed circuit board is built using surface mount resistors, capacitors and operational amplifiers to construct the unity gain source follower circuit. The headstage is made water-proof with a combination of epoxy, parafilm and a synthetic rubber putty. We have successfully used this device to record local field potentials and stimulate different brain regions simultaneously via independent channels in rats swimming in a water maze. The total cost is < $30/unit and can be manufactured readily.

Design and Construction of a Cost Effective Headstage for Simultaneous Neural Stimulation and Recording in the Water Maze

Headstage preamplifiers and source followers are commonly used to study neural activity in behavioral neurophysiology experiments. Available commercial products are often expensive, not easily customized, and not submersible. Here we describe a method to design and build a customized, integrated circuit headstage for simultaneous 4-channel neural recording and 2-channel simulation in awake, behaving animals. The headstage is designed using a free, commercially available CAD-type design package, and can be modified easily to accommodate different scales (e.g. to add channels). A customized printed circuit board is built using surface mount resistors, capacitors and operational amplifiers to construct the unity gain source follower circuit. The headstage is made water-proof with a combination of epoxy, parafilm and a synthetic rubber putty. We have successfully used this device to record local field potentials and stimulate different brain regions simultaneously via independent channels in rats swimming in a water maze. The total cost is < $30/unit and can be manufactured readily.

Investigation of source-follower type analog buffer using low temperature poly-Si TFTs

A new source follower circuit using low-temperature polycrystalline silicon thin film transistors (LTPS-TFTs) as analog buffer for the integrated data driver circuit of active matrix liquid crystal displays (AMLCDs) and active matrix light emitting diodes (AMOLEDs) is proposed and measured. Threshold voltage compensation circuit with two n-type thin film transistors, a capacitor, and four switches structure is used to enhance image quality for the display. The threshold voltage difference of driving TFTs and the unsaturated of output voltage are eliminated in this circuit. An active load is added and a calibration operation is applied to study the effects on the source follower circuit, the transistor operation mode region is also discussed. The proposed circuit is capable of minimizing the variation from both the signal timing and the device characteristics through the simulation and measured results.

An On-Chip Multi-Channel Rail-to-Rail Signal Monitoring Technique for Sub-100-nm Digital Signal Integrity

A compact on-chip signal monitor circuit uses voltage mode sensing by a source follower circuit with small input device geometry, followed by a current-mode sample and a hold circuit that is connected to a shared current output bus. A prototype signal monitor circuit demonstrated a 1.1-GHz effective bandwidth for 1.0-V full-swing digital signals in a 90-nm CMOS technology, where the monitor used 2.5-V I/O CMOS transistors and occupied a 30μm x 120 μm silicon area. We also showed that such signal monitor circuits can be tailored to sense of power-supply, ground, as well as full-swing logic signal wirings, and form an array with a single current output. Therefore, an on-chip multi-channel signal monitor enables multiple-points as well as multiple-voltage domain waveform acquisition for the purpose of the in-depth study of digital signal integrity.

Temperature characteristics of electret condenser microphones

Electret condenser microphones for mobile system terminals should be more robust than those for ordinary consumer equipment. Generally, the diaphragm electret can achieve flat temperature characteristics with respect to sensitivity because the temperature dependence of the diaphragm stiffness and gain characteristics of the FET offset each other. However, the fixed electrode electret using a PET diaphragm is not sufficiently robust with respect to temperature because the PET membrane has the same temperature coefficient as FETs, so there is no offsetting and it is difficult to compensate the temperature characteristics. In order to improve robustness, this paper proposes a temperature dependence evaluation method for acoustic characteristics of the electret condenser microphone. It then reports the temperature dependence of the dominant parameter that affects the sensitivity of the microphone and describes a method to design a microphone with stable temperature characteristics. In a new trial, silicon, an inorganic material, is applied to the diaphragm. It is subsequently demonstrated that an impedance converter composed of a source-follower circuit is effective for a high temperature environment of up to 80°C. Finally, the possibility of an electret condenser microphone with flat temperature characteristics is proposed.

A source-follower type analog buffer using poly-Si TFTs with large design windows

New simple source follower circuits using low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) as analog buffers for the integrated data driver circuit of active-matrix liquid crystal displays and active-matrix light emitting diodes are discussed. In addition to the threshold voltage difference of driving TFTs, the unsaturated of output voltage arisen from the significant subthreshold current will also result in the difficulty of the buffer circuit design. The proposed circuit is capable of minimizing the variation from both the signal timing and the device characteristics.

0.1-µm-Gate Metamorphic High-Electron-Mobility Transistor on GaAs and Its Application to Source-Coupled Field-Effect Transistor Logic

The device performances of 0.1-µm-gate InxGa1-xAs/InyAl1-yAs metamorphic high-electron-mobility transistors (MM-HEMTs) on GaAs substrates, depending on the indium composition (XIn), have been investigated. By reducing the XIn, the gate-to-drain breakdown voltage (BVgd) of the MM-HEMT can be improved, while the transconductance (gm) and the current gain cut-off frequency (fT) decrease because of a reduction in electron mobility of the InxGa1-xAs channel. The balanced values of gm of 900 mS/mm, fT of 166 GHz and BVgd of 5.2 V for the MM-HEMT with XIn of 0.45 have been obtained. The propagation delay (tpd) of a source-coupled field-effect transistor logic (SCFL) inverter implemented by MM-HEMTs rapidly increases with decreasing XIn, due to the increase in series resistance of the Schottky diode in the source-follower circuit.

A high-sensitivity CCD image sensor using source follower circuit with actively controlled gain characteristics

A high-sensitivity charge coupled device (CCD) image sensor that utilizes a new output structure has been developed. The structure utilizes an enhancement inverter, a coupling capacitor, and resistors in addition to the conventional source follower. The output of the source follower is inverted and ac component of that signal is fed back to the gate of the load transistor of source follower to modulate the impedance. The overall gain improvement can be estimated from simple small-signal analysis and the results match well to the circuit simulation. A 1/4 in. 250,000 pixels color CCD image sensor was fabricated employing the new output circuit. The fabrication process is same to that for conventional CCD image sensors since the inverter in this circuit consists of enhancement mode transistors. It is observed that 14% of sensitivity improvement in the CCD image sensor is achieved by the new structure and the linearity shows no distortion compared to conventional image sensors in the full range of imaging illumination.

Internal noise in miniature electret microphones

Modern miniature electret microphones normally include an internal amplifier to buffer the very high electrical impedance of the electret motor. This amplifier, usually an FET source follower circuit, generates a part of the noise in the microphone output signal. The electrical noise originates in the semiconductor and in the resistive components of the electrical circuit. Recent developments have reduced the electrical noise considerably so that it is no longer the dominant source. The other noise sources are the resistive components of the mechanical and acoustical impedances within the microphone. This paper describes recent work and special measurement methods that have helped to identify and reduce the acoustical noise components.

Audiogenic kindling in the Wistar rat: a potential model for recruitment of limbic structures

Repetitive high intensity (110 dB) sound stimulation induces a forebrain-kindling phenomenon in animals predisposed to sound induced seizures. Wistar audiogenic rats (WARs) have been reported to develop a mixed brainstem-limbic seizure pattern, after more than five to ten stimuli. Besides the original brainstem wild running and tonic-clonic seizures, new behavioral patterns appear resembling those of electrical amygdala kindling. Although audiogenic kindling is a well-known phenomenon, electrographic limbic recruitment during the kindling has never been reported. Our objective was to use electrophysiology to test the hypothesis of gradual and sequential involvement of the amygdala and then cortex during audiogenic kindling. We used video-EEG recordings with cortical and deep electrode implants (inferior colliculus and basolateral amygdaloid nuclei) during audiogenic kindling on eight WARs, and their respective controls, submitted to a protocol of three acoustic stimuli per day. A new design for ‘on site’ source follower circuits was used in order to minimize noise during the recording of EEG data from the wild running episode and the subsequent tonic-clonic or motor limbic seizures. The video-EEG equipment assembled allowed synchronous recordings of both behavior and EEG. WARs first recordings showed electrodecremental responses after seizure onset and a probable epileptiform activity, particularly in the inferior colliculus, during the tonic phase of seizure. All animals showed very similar polyspike-wave activity in the amygdala, after behavioral seizure patterns (Racine’s scale) occurred. The morphology of such epileptiform EEG activity is very similar to that reported for electrical amygdala kindling. Also, when audiogenic kindling continued, both inferior colliculus and cortical electrodes presented high amplitude and synchronized epileptiform polyspike activity.