Showing papers on "Pulse-frequency modulation published in 2010"

A Dual-Mode Single-Inductor Dual-Output Switching Converter With Small Ripple

Abstract: Single-inductor dual-output (SIDO) switching converters always suffer from large ripple and severe cross-regulation problem, when a large inductor current is switched between two outputs. This paper proposes a novel fly capacitor method for SIDO converters to reduce the output ripple and spike. An adaptive common-mode control is presented to suppress the cross-regulation problem. A duty-ratio-based current estimation method is proposed to detect the load current, and the converter can automatically switch between pulsewidth modulation and pulse-frequency modulation modes. The two outputs of the converter are specified for 1.2 V/400 mA and 1.8 V/200 mA with input voltage ranging from 2.7 to 5 V. The chip has been fabricated on a 0.25-? m CMOS mixed-signal process. The conversion efficiency is 82% at a total output power of 840 mW, while the output ripple is about 20 mV and spike is less than 40 mV. The maximum overshot voltage during load response is 50 mV.

Event-based 64-channel binaural silicon cochlea with Q enhancement mechanisms

Abstract: This paper describes an event-based binaural silicon cochlea aimed at spatial audition and auditory scene analysis. The chip has a matched pair of 64-stage cascaded analog second-order filter banks with 512 pulse-frequency modulated (PFM) address-event representation (AER) outputs. The spectral selectivity is sharpened through 2 different on-chip methods: an on-chip local Q DAC and an on-chip spatial sharpening through nearest neighbour lateral inhibition. The fabricated chip in a 4-metal 2-poly 0.35um CMOS process consumes peak 25mW power for the digital circuits and 33mW for the analog core. Dynamic range to produce PFM output is 36dB (25mVpp to 1500mVpp at microphone preamp output). Event timing jitter is 2us for 250mVpp input. The peak output bandwidth is 10M events per second (eps) but typical speech scenarios show rates of 20keps.

Current mode buck converter with fixed PWM/PFM boundary

Abstract: A current mode Boost converter is disclosed. The Boost converter operates in a pulse width modulation (PWM) mode or a pulse frequency modulation (PFM) mode. To prevent a load current with various probable magnitudes from varying a decision boundary between the PWM mode and the PFM mode, the Boost converter adaptively adjusts a trigger condition for the PFM mode according to a mean value of an inductor current or AC components of an inductor current of an inductor and a slope compensation current.

Multimode Digital Controller for Synchronous Buck Converters Operating Over Wide Ranges of Input Voltages and Load Currents

Abstract: This paper describes a digital pulsewidth modulation/pulse-frequency modulation (PWM/PFM) controller with input-voltage feedforward (IVFF) for synchronous buck dc-dc converters. The controller includes automatic PWM/PFM mode switching and effective synchronous operation with a minimum number of active components and without the need for current sensing in PFM mode of operation. IVFF improves efficiency and dynamic performance over a wide range of input voltages. Controller parameters, including the PWM switching frequency, the PFM pulse period, and the mode transition point are programmable, which enables efficiency optimization. Experimental results are shown for a synchronous buck converter with 5-12 V input voltage, and 1.3 V, 0-10 A output.

Multilevel Inverters: A Comparative Study of Pulse Width Modulation Techniques

Abstract: The multilevel inverter topology gives the advantages of usage in high power and high voltage application with reduced harmonic distortion without a transformer This paper presents a comparative study of nine level diode clamped inverter for constant Switching frequency of sinusoidal Pulse width Modulation and sinusoidal Natural Pulse width Modulation with switching frequency Optimal Modulation

Spread spectrum clock generator, spread spectrum clock generating method, and circuit, image reading device and image forming apparatus using the spread spectrum clock generator

Abstract: The spread spectrum clock generator (SSCG) includes a phase comparator detecting phase difference between input clock and feedback clock; a charge pump supplying current depending on the phase difference; a loop filter converting the current to smoothed voltage; a voltage controlled oscillator generating a spread spectrum clock signal depending on the smoothed voltage; and a modulation signal generator generating modulation signal having amplitude depending on a modulation width set value. The SSCG further includes a modulation width detector detecting modulation width of the spread spectrum clock signal while comparing the modulation width with a modulation width target value to update the modulation width set value to narrow difference between the detected modulation width and the modulation width target value, followed by feeding back the updated modulation width set value to the modulation signal generator.

Comparative evaluation of modified pulse width modulation schemes of Z-source inverter for various applications and demands

Abstract: This paper presents a comparative evaluation of five different methods of modified pulse width modulation schemes to control the recently developed buck-boost type Z-source inverter. Since its inception, different control techniques have been proposed to insert the shoot-through periods in the traditional switching waveform of the power switching devices. Simple boost control, maximum boost control, constant boost control and modified space vector modulation based control methods have been presented by world wide researchers for various types of loads and applications. However, the detailed comparative evaluation has not been reported to select the suitable control method according to the application and demand. In this paper, for the common boost factor and modulation index, the output voltage, output current, output line harmonics profile of the inverters with different PWM schemes powered by the same dc power supply and three phase RL load were conducted. Comparison results are analyzed for two control variables (modulation index and boost factor) and are evidently reported. For each method, the boost factor, voltage gain, duty ratio and voltage stress across the switches are expressed and the relationships among them are analyzed. By comparing them, proper control method can be adapted according to the requirement of different applications and demands. Keywords: Z-source inverter, buck-boost, pulse width modulation (PWM), modified space vector modulation (MSVM), shoot-through, voltage stress.

System, method and apparatus to transition between pulse-width modulation and pulse-frequency modulation in a switch mode power supply

Abstract: A switch mode power supply (SMPS) has optimized efficiency over an entire operating range, from no load to full load, by transitioning between pulse frequency modulation (PFM) and pulse width modulation (PWM) for control of the SMPS depending upon load current. Accurate, smooth, and seamless transitions between PFM and PWM modes of operation occur at a preset load current(s), PFM operation improves efficiency during light load conditions, and PWM has better efficiency at higher load currents. This is advantageous in battery powered applications, and thereby results in a longer time before battery replacement or recharge is necessary.

ELF/VLF wave generation via ionospheric HF heating: Experimental comparison of amplitude modulation, beam painting, and geometric modulation

Abstract: [1] Generation of ELF/VLF radio waves (300 Hz to 10 kHz) is achievable via modulation of natural currents in the lower ionosphere with high-power HF (2–10 MHz) heating Recently, Cohen et al (2008b) put forth an alternative to conventional amplitude HF power modulation, therein referred to as geometric modulation, in which the HF ionospheric heating beam is geometrically steered at the desired ELF/VLF frequency, and found 7–11 dB enhanced amplitudes, and ∼14 dB directional dependence for the thus generated ELF/VLF waves, compared to vertical amplitude modulation In this paper, we quantitatively compare amplitude modulation, geometric modulation, and a previously proposed technique known as beam painting, wherein the HF beam is rapidly moved over a wide area during the on portion of amplitude modulation in order to create a larger heated region in the ionosphere We experimentally analyze both the total generation and the directionality, ie, the suitability of each technique to direct signals along a chosen azimuth Among the three methods, geometric modulation is found to be uniquely well suited for both goals We also conduct experiments to investigate two particular physical effects and their role in generation efficacy: that of heat-cool duty cycle and the oblique angle of the HF heating beam It is found that both duty cycle and the oblique angle of the beam have small but counteracting impacts, consistent with the notion that the primary physical process responsible for generation enhancement in geometric modulation is that of formation of an effective multielement phased array

A Novel Return-to-Zero FSK Format for 40-Gb/s Transmission System Applications

Abstract: In this paper, we present the generation, the detection and the performance evaluation of a novel return-to-zero frequency shift keying (RZ-FSK) format for 40 Gb/s transmission. Non-return-to-zero (NRZ) FSK signal is generated by using two continues-wave (CW) lasers, one Mach-Zehnder modulator (MZM) and one Mach-Zehnder delay interferometer (MZDI). A RZ-FSK signal is successfully generated by cascading a dual-arm MZM, which is driven by a sinusoidal voltage at half of the bit rate. The demodulation can be simply achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection. By numerical simulation, two types of frequency modulation schemes using MZM or PM, and impact of the frequency tone spacing (FTS) of the generated FSK signal are discussed. The proposed scheme shows that the novel frequency modulation format offers a few transmission advantages comparing with than that of the other traditional modulation formats, such as RZ and differential phase-shift keying (DPSK), under varying dispersion management. The performance analysis of RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is introduced. We experimentally demonstrate, transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal, clearly validating the feasibility of all optical signal processing of high-speed RZ-FSK signal. Moreover, we investigate the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF), under the post-compensation management scheme. Since the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying), it can be employed in the context of the combined modulation format to decrease the data rate or enhance the symbol rate. It can also be utilized in the orthogonal label-switching as the modulation format for the payload or the label.

Switching Mode Power Supply Control

Abstract: A method for controlling a switching converter is disclosed whereby the switching converter is configured to convert an input voltage into an output voltage supplied to a load in accordance with a switching signal, The switching converter is configured to operate in a pulse width modulation mode or, alternatively, in a pulse frequency modulation mode. When operating in the pulse width modulation mode, generating, as the switching signal, a pulse width modulated (PWM) signal of a pre-defined constant switching frequency. The PWM signal has a duty cycle that is regulated such that the output voltage of the switching converter matches, at least approximately, a desired output voltage under the condition that the duty cycle being regulated such that it does not fall below a predefined minimum duty cycle. The output voltage is monitored and switched over to the pulse frequency modulation mode when the output voltage exceeds a predefined first threshold. The method further comprises, when operating in the pulse frequency modulation mode, monitoring the output voltage and generating, as the switching signal, a series of pulses of a predefined constant pulse length. A pulse is generated each time the output voltage falls to a predefined second threshold and monitoring the frequency of the switching signal and switching to the pulse width modulation mode when the frequency of the switching signal exceeds a predefined frequency threshold.

Frequency control circuit and method for a non-constant frequency voltage regulator

Abstract: A non-constant frequency voltage regulator includes a constant-time trigger to generate a pulse width modulation signal, a current generator to provide a first current to set a constant on-time or a constant off-time for the pulse width modulation signal, and a frequency control circuit to detect the pulse width of a phase node voltage, compare the pulse width with the constant on-time or the constant off-time set by the first current to generate a second current, and add the second current to the first current to supply to the constant-time trigger to control the frequency of the pulse width modulation signal.

Weak etalon effect in wave plates can introduce significant FM-to-AM modulations in complex laser systems

Abstract: The conversion of frequency modulation to amplitude modulation (FM-to-AM) effect is harmful to the high power laser facility based on the phase modulation technique. The FM-to-AM effect of phase modulation pulse induced by the weak etalon effect in wave plates was investigated theoretically and experimentally. A bulk phase modulator with a modulation frequency of 9.2GHz was employed. The numerical simulation results show that the FM-to-AM effect with a temporal modulation depth of 2.5% and 29.7% on the top of the pulse shape was induced by the weak etalon effect in half-wave plate with thickness of 1mm and residual reflectance ratio of 0.5% for 1 pass and 12 passes respectively. On the same condition, the temporal modulation depth is 3.0% and 23.4% respectively in the experiment. The results are in good agreement with numerical simulation results. To our knowledge, it is the first time to introduce the weak etalon effect in wave plates for a complex phase modulation laser system.

Led backlight system

Abstract: A method and system for modifying the pulse width modulation frequency for controlling the backlit illumination intensity of a liquid crystal display (14). The modified pulse width modulation frequency may be selected to reduce distortion in the display (14) while allowing for a wide range of dimming settings for the display (14). A pulse width modulation signal (95) may be also be phase shifted such that a string of light sources (110-115) may be sequentially activated to generate a effective frequency greater than that of the frequency of the pulse width modulation signal (95).

Pulse width modulation based signal format for visible light communications

Abstract: A pulse-width modulation (PWM) based modulation format is proposed for visible light communication (VLC) system using illumination light-emitting diodes (LEDs). A pulse-position modulation (PPM) data signal is employed over PWM dimming (brightness) control signal. The PPM data pulses are recovered from the received optical signal over a distance of 20 cm.

Experimental study of an all-fiber laser actively mode-locked by standing-wave acousto-optic modulation

Abstract: We report an experimental study of an actively mode-locked erbium-doped all-fiber laser, based on a standing-wave acoustically-induced superlattice modulation. Our experiments involve the characterization of the laser as a function of the active fiber length, and with different types of delay line fibers. The effect of the modulation on the laser performance was also investigated. Narrower pulses were obtained at higher modulation depths, normal dispersion, and shorter lengths of active fiber. Optical pulses of 160 mW peak power and 630 ps temporal width were obtained at 9 MHz repetition rate.

Push-Pull Modulation of a Composite-Resonator Vertical-Cavity Laser

Abstract: The two coupled optical cavities within a vertical-cavity surface-emitting laser have the unique ability to modulate the spatial distribution of the longitudinal optical mode, without changing the total photon density in the laser cavities, by simultaneously directly modulating the two optical cavities exactly out-of-phase. A rate-equation analysis predicts that this condition, which we term push-pull modulation, exhibits a superior modulation response than that of conventional direct modulation. The push-pull modulation can enable high-speed operation with low power consumption, as a large modulation bandwidth can be achieved independent of the total photon density and/or the injection dc current. Experimental evidence of spatially changing the longitudinal mode is presented, and push-pull modulation at 2.5 Gb/s is demonstrated for the first time.

Energy harvesting system

Abstract: An energy harvesting system includes: an energy harvesting unit for converting energy from a natural energy source into an electrical power signal; a power point tracking unit including a current tracing module capable of detecting a current of the electrical power signal, and a boundary control module; a microcontroller including a voltage detecting module capable of detecting a voltage of the electrical power signal, and a computing module for determining a maximum power point with reference to the voltage and the current of the electrical power signal, the boundary control module generating a switch control voltage signal with reference to the maximum power point; a storage unit capable of storing energy; and a pulse frequency modulation regulator for converting the electrical power signal into an intermediate signal with reference to the switch control voltage signal for subsequent storage of energy of the intermediate signal in the storage unit.

An integrated step-down DC-DC converter with low output voltage ripple

Abstract: An integrated low-output-ripple step-down DC-DC converter, which cascades a Buck converter with a low-dropout regulator (LDO), is presented. The output of the Buck converter can be used to supply digital circuits, while the LDO output is used to power analog circuits. The designed Buck converter can adaptively and automatically switch between the pulse-width modulation (PWM) and pulse-frequency modulation (PFM) to improve the conversion efficiency over the whole load current range. The chip was implemented by TSMC 0.35µm 2P4M polycide CMOS process. The measured maximal load current of the Buck converter was 280 mA, and the measured LDO maximal load current was 100 mA.

Backlight system for a display

Abstract: A method and system for modifying a pulse width modulation signal for controlling the backlit illumination intensity of a liquid crystal display. The modified pulse width modulated signal may be selected to operate with at least one pulse having a first duty cycle with the remaining pulses in the pulse width modulation signal having a second duty cycle across a selected number of pulses making up a given time period (i.e., frame). By utilizing more than one duty cycle for the pulses of the pulse width modulated signal to drive light sources in a display during a given frame, the overall number of backlit illumination intensities for the liquid crystal display may be increased. By distributing the differing pulse duty cycles within a group of pulses of within a frame, visible artifacts may be reduced.

Adaptive On-Time Converters

Abstract: Pulse frequency modulation (PFM) converters are fast in response and simple in design and implementation because compensation is not required. However, the large variation of switching frequency during operation introduces electromagnetic interference (EMI) problems. This article proposes a mixed analog and digital adaptive on-time (AOT) controller for PFM converters so that the switching frequency can be maintained constant adaptively, while the transient response is not degraded. The transient response is handled by an analog controller, which is fast. The switching frequency regulation is implemented by a digital microcontroller.

A Tightly Regulated Triple Output Asymmetrical Half Bridge Flyback Converter

Abstract: In this paper, a tightly regulated triple output asymmetrical half bridge flyback (ASHF) converter is proposed. In order to regulate all output voltages, pulse frequency modulation (PFM), pulse width modulation (PWM) and phase delay (PD) are used simultaneously. In comparison with the conventional PWM-PD method, the interactions among the control variables are minimized and the operating range is increased. By the utilization of a multi winding transformer, the auxiliary transformer and the blocking capacitor are eliminated and the size and cost of the proposed converter is reduced. The operation principle of the converter is explained and the modes of operation are investigated. Based on the results, the steady state characteristics of the converter are explored. A 24V/10A, 12V/5A, 5V/10A hardware prototype is built and tested to verify the analysis results and the voltage regulation of the triple outputs of the proposed converter.

FPGA-based combined PWM-PFM technique to control DC-DC converters

Abstract: This paper describes a combined Pulse Width Modulation (PWM)-Pulse Frequency Modulation (PFM) technique implemented in a Field Programmable Gate Array (FPGA) to control DC-DC converters. This technique changes the mode of operation from PWM to PFM with the change in the load condition. The efficiency of the proposed technique is determined by implementing a DC-DC converter and calculating the conduction losses, switching losses, and ripple voltages at different load values. Furthermore, the efficiency of the converter based on the proposed technique is compared to the efficiency of processor-based implementation. The results show that the efficiency of the converter with the FPGA-based technique is higher than the efficiency of the converter with processor based technique.

Fixed-frequency control circuit and method for pulse width modulation

Abstract: A fixed-frequency control circuit and method detect the difference between the frequency of a pulse width modulation signal and a target frequency to adjust a current used to determine the on-time or off-time of the pulse width modulation signal, such that the frequency of the pulse width modulation signal is stable at the target frequency.

Control apparatus and method for Boost type switch converter

Abstract: The invention discloses a control method of a Boost type switching converter, after being done with sampling processing, input current and output voltage are used as negative feedback to control a power switching pipe of the Boost type switching converter, which leads the switching converter to be kept in an excellent system transient response and control precision, pulse frequency modulation is achieved under light loads, and the power conversion efficiency is increased The invention further discloses a control device, which comprises a Boost type switching converter, a first acquisition circuit, a second acquisition circuit, a transconductance type amplifier, an operational circuit, a comparator and a timer logic circuit, thereby achieving the above control method

High efficiency DC-DC converter with auto-mode transition for mobile SOC applications

Abstract: This paper describes an integrated dual-mode DC-DC converter and its seamless auto-mode transition between the pulse frequency modulation (PFM) and the pulse width modulation (PWM), resulting in reduced inductor current peak and output voltage overshoot. The key idea of auto-mode transition is to keep a control voltage level as a constant by forming a negative feedback loop with a compensator in the PFM operation. The DC-DC converter was implemented in the L6LP (65nm) process and achieved maximum 91% of measured efficiency for the load current ranging from 5mA to 200mA.

Pulse frequency modulation with soft-switching flyback single-stage inverter

Abstract: A Pulse Frequency Modulation (PFM) with Zero-Current-Switching (ZCS) flyback inverter is proposed in this paper. By using half-wave quasi-resonant ZCS flyback resonant converter and PFM control, this topology significantly alleviates switching losses. A detailed analysis revealed nonlinearity in the power stage when the secondary side inductance gets smaller. A modified structure with a secondary side MOSFET is also proposed to solve this issue. Finally, the experimental results of 250W converter are provided.

Digital boost feedback voltage controller for switch-mode power supplies using pulse-frequency modulation

Abstract: A controller produces high-side and low-side control signals. The high and low-side signals are used to switch high-side and low-side transistors in the power stage to control the voltage across the power stage output capacitor of the power stage. A boost feedback charge pump receives the low or high-side signal to increase the charge on a charge pump output capacitor. The controller is configured to send Pulse Frequency Modulation (PFM) high and low-side signals that control the voltage on the power stage output capacitor and charge the charge pump output capacitor. The controller is also configured to send boost feedback (BFB) high and low-side signals that charge the boost feedback capacitor, but are designed to not significantly change the charge on the power stage output capacitor.