Topic
Pulse-frequency modulation
About: Pulse-frequency modulation is a research topic. Over the lifetime, 4151 publications have been published within this topic receiving 53039 citations. The topic is also known as: PFM.
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TL;DR: In this article, the authors proposed a push-pull modulation, which can enable high-speed operation with low power consumption, as a large modulation bandwidth can be achieved independent of the total photon density and injection dc current.
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.
23 citations
Patent•
13 Apr 1983
TL;DR: In this paper, a method and apparatus for detecting a frequency change of a light of the invention modulates the scattered light from the object of measurement using an acousto-optic modulator or the like, heterodyne-detects the reflected light after modulation to provide an electrical signal having a frequency (fd - fm) which is the difference between the Doppler frequency fd and the modulation fre-quency fm.
Abstract: LIGHT FREQUENCY CHANGE DETECTING METHOD AND APPARATUS Abstract of the Disclosure: A method and apparatus for detecting a frequency change of a light of the invention modulates the scattered light from the object of measurement using an acousto-optic modulator or the like, heterodyne-detects the scattered light after modulation to provide an electrical signal having a frequency (fd - fm) which is the difference between the Doppler frequency fd and the modulation fre-quency fm, passes this electrical signal to a filter while changing the modulation frequency fm, and obtains the modulation frequency fm at which the signal voltage is the largest or the smallest, that is, the Doppler frequency fd.
23 citations
TL;DR: The root cause of this effect is an error in the determination of the cross points, due to the sampled nature of the signal, and a method to compensate for it is described and it is shown that by interpolating the signal and estimating theCross points the signal quality can be significantly improved.
Abstract: The trend in transmitter systems is to move the digital domain closer toward the antenna using digital modulators and drivers to reduce circuit complexity and to save power. One promising approach is the use of RF pulse width modulation (RF PWM). Unfortunately purely digital discrete time RF PWM suffers from aliasing problems which limit the achievable resolution. For a 40 MHz bandwidth signal at 2.6 GHz carrier frequency for example the achievable signal quality is limited to $\sim$ 43 dBc. This paper describes the root cause of this effect, an error in the determination of the cross points, due to the sampled nature of the signal and proposes a method to compensate for it. It is shown that by interpolating the signal and estimating the cross points the signal quality can be significantly improved. The interpolation is simplified by interpolating the decomposed outphasing signals instead of the full signal. This has the advantage that a constant instead of a phase modulated reference function can be used. It is shown that by simple cross point estimation the signal quality can already be improved to 65 dBc. When either considering a second modulator or when using a delta sigma like noise shaping architecture the signal quality can be further enhanced to 75 dBc.
23 citations
TL;DR: The proposed average current control (ACC), proposed accuracy-enhanced on-chip current sensors, and the adoption of a dual-phase power stage substantially improves the reliability of the proposed PWM-based dual- phase LED driver.
Abstract: Light-emitting diode (LED) drivers for automotive lighting applications adopt pulsewidth modulation (PWM) vis-a-vis pulse frequency modulation because its ensuing electromagnetic interference (EMI) spectrum is predictable and easily mitigated. Nevertheless, present-day PWM control schemes adopted in LED drivers suffer from imprecise output current and subharmonic oscillation, which compromises reliability. In this paper, we present a PWM-based LED driver that features low EMI and high reliability. These attributes are achieved by our proposed average current control (ACC), proposed accuracy-enhanced on-chip current sensors, and our adoption of a dual-phase power stage. The ACC eliminates subharmonic oscillation by means of considering the complete inductor current profile vis-a-vis peak current adopted elsewhere. Also by means of the dual-phase power stage, good current balance and small current ripple are obtained. Collectively, the aforesaid substantially improves the reliability. To improve electromagnetic compatibility (EMC), the proposed accuracy-enhanced on-chip current sensors are monolithically realized with the ACC and power transistors—to the best of our knowledge, the first for a PWM-based dual-phase LED driver. The prototype LED driver, realized in a 130-nm BCDLite process, has an input voltage range of 5–16 V, output to drive 1–3 series-connected LEDs, provides a current regulation accuracy of at least 96.2%, dimming frequency up to 20 kHz, features a peak power efficiency of 94.7%, settling time of $5~\mu \text{s}$ , LED current range of 0.4–2.4 A, and current ripple factor of 8%. When benchmarked against the state-of-the-art LED drivers, our design features the highest peak power efficiency, the shortest settling time, highest current driving capability, and the lowest current ripple factor.
23 citations
TL;DR: In this paper, the influence of current modulation on different feedback-induced transverse-mode regimes was studied for vertical-cavity surface-emitting laser (VCSEL) with optical feedback.
Abstract: Vertical-cavity surface-emitting lasers (VCSELs) with optical feedback are known to exhibit different transverse-mode regimes depending on the injection current. Close to threshold a VCSEL operates on the fundamental transverse mode, while for larger injection the dynamics is often multimode, with the optical feedback inducing either in-phase or anti-phase transverse mode oscillations. In this paper, we study numerically the influence of current modulation on these different feedback-induced transverse-mode regimes. The modulation amplitude and period are taken as control parameters. We find that the in-phase and anti-phase regimes are robust under weak modulation. As the modulation amplitude increases, there is a transition to a dynamics governed by the current modulation, where the total output power follows the injection current and there is either single-mode or in-phase multimode behavior. However, the effect of the current modulation depends on the modulation period. Under fast modulation, the laser cannot follow the modulation and the optical-feedback-induced effects are dominant. On the contrary, under slow modulation there is a superposition of modulation and feedback effects, with the total output following the modulated current and an underlying transverse-mode behavior mainly determined by the optical feedback. A resonant behavior was observed for modulation periods close to the internal oscillation period. In this case, current modulation induces pulsing output intensity with single-mode or in-phase multimode behavior.
23 citations