KEYWORDS: Analog electronics, Sensors, Interferometry, Signal detection, Signal processing, Switching, Semiconductor lasers, Computer intrusion detection, Photodiodes, Linear filtering
We present a self-mixing interferometer (SMI) vibrometer developed around a laser diode with a simple and compact analog processing of the fringe signal, and show that this instrument can readily detect ambient vibrations—which adversely affect mechanical material-working lathes. In addition, we find out that the vibrometer is an excellent intrusion detector, capable of discovering a man stepping several meters away from the sensor, thus hinting at an SMI application as an antithief sensor.
LNA's (Low Noise Amplifier) are widely used in wireless portable personal communication systems; the LNA noise directly affects the overall system performances. Here it is shown how the Noise Figure of a RF (Radio Frequency) Receiver can be reduced while satisfying the common constraints of impedance matching at the input, low power consumption and good linearity. The proposed Noise Figure reduction technique is based on the cold resistance approach and negative or positive feedback; a single BJT LNA, derived from the common base configuration, is considered. The Noise Figure reduction is obtained over a wide frequency band of operation, and is thus suitable for Multistandard applications. Different LNA feedback topologies are compared. It is shown that a Noise Figure lower than the limit of the common base configuration can be achieved, along with a current consuption of a few mA, over a wide frequency band of operation. Noise Figure calculations and circuit simulation results are presented and compared.
A model for the 1/f noise in passive components undergoing time-varying bias is proposed. One-port devices exhibiting 1/f noise are considered, e.g. carbon or polysilicon resistors. Starting from the Hooge’s formula, that holds when the component is operated under DC bias, it is shown that the noise current is simply proportional to the product between the conductivity fluctuation and the time-dependant voltage applied to the component. In other words, the 1/f noise in passive components under time-varying bias arises from the intermodulation between the stochastic process 'conductivity fluctuation' and the voltage applied to the component. Detailed calculations of both autocorrelation function and power spectrum of the resulting noise current are given; different time dependences of the voltage applied to the component are considered. Of particular relevance is the case of sinusoidal voltage; in this case the resulting noise current is a cyclostationary stochastic process and its behaviour can be conveniently described by the cyclic autocorrelation functions or by the cyclic power spectra. A circuit is built to measure the actual power spectra of the noise current of carbon resistors under constant or periodic voltage bias, in order to verify the results obtained from the proposed model. Very good agreement between theory and experiment is observed, and this fact supports the proposed model for 1/f noise in passive components under time-varying bias. The conclusion is that the physical origin of 1/f noise in passive components does not depend on external bias, nor in DC nor when a time-varying signal is applied to the component.
In a previous paper, we proposed a new approach to the optical interconnection of telephone- card signals. Our approach was developed around a multimode-fiber star coupler as the optical bus, and standard optoelectronic components for transmitters and receivers. In this paper, we report on recent developments of two practical demonstrators of the above concept, namely: (1) an optical backplane for 24 X 24 I/O signals interconnection operating at 1.1 Gbit/s, with a transmitter and receiver fabricated in hybrid technology and fully connectorized to the star coupler; (2) an optical clock distribution capable of operating up to 4.5 Gbit/s with < 5% amplitude droop. Common to both units are a good S/N ratio (> 25 dB), very little time unbalance between channels (< 15 ps), and an inherent bandwidth-length product of 40 Gbit/s(DOT)m as determined by the coupler and fiber pigtails.
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