Amplified Output Signal Research Articles

Intrinsic thin film stresses in multilayered imaging pixels

When thin film devices are integrated in display or imaging arrays, the intrinsic mechanical stresses in the films can be severe enough to cause the films to either crack or even peel off the underlying substrate layer. This is a particular concern in large area x-ray imaging applications based on molybdenum/amorphous silicon (Mo/a-Si:H) Schottky diodes. This family of image sensors can be used for direct detection of x rays without the need for a phosphor layer [W. Zhao and J. A. Rowlands, Med. Phys. 22, 1595 (1995)]. In these sensors, the interaction of x-ray photons with Mo leads to injections of high energy electrons into a reverse-biased a-Si:H depletion layer, thereby producing an amplified output signal due to charge multiplication. The generated charge is read out by a thin film transistor (TFT) which is composed of intrinsic amorphous silicon (i-a-Si:H) as the active channel layer, silicon nitride (a-SiNx) as the insulating layer, and highly doped microcrystalline silicon (n+μc-Si:H) as the contact layer. For example, the i-a-Si:H layer is in compressive stress with a magnitude of 0.116 GPa, whereas low temperature, low resistivity n+μc-Si:H layer is in compressive stress of 1.47 GPa. The a-SiNx layer is in tensile stress of 0.222 GPa. The heavy metals used in the x-ray detector, such as Mo and chromium (Cr) (deposited at 5 mTorr), are found to be in tensile stress of 0.807 and 0.575 GPa, respectively. This article presents the internal mechanical stresses in thin film devices used in x-ray imaging, and more importantly, how the total film stress can be reduced without undermining device performance.

Directional hearing system

A directional acoustic receiving system is constructed in the form of a necklace including an array of two or more microphones mounted on a housing supported on the chest of a user by a conducting loop encircling the user's neck. Signal processing electronics contained in the same housing receives and combines the microphone signals in such a manner as to provide an amplified output signal which emphasizes sounds of interest arriving in a direction forward of the user. The amplified output signal drives the supporting conducting loop to produce a representative magnetic field. An electroacoustic transducer including a magnetic field pick-up coil for receiving the magnetic field is mounted in or on the user's ear and generates an acoustic signal representative of the sounds of interest. The microphone output signals are weighted (scaled) and combined to achieve desired spatial directivity responses. The weighting coefficients are determined by an optimization process. By bandpass filtering the weighted microphone signals with a set of filters covering the audio frequency range and summing the filtered signals, a receiving microphone array with a small aperture size is caused to have a directivity pattern that is essentially uniform over frequency in two or three dimensions. This method enables the design of highly-directive hearing instruments which are comfortable, inconspicuous, and convenient to use. The invention provides the user with a dramatic improvement in speech perception over existing hearing aid designs, particularly in the presence of background noise and reverberation.

A pulse generator simulating Ge-detector signals for dead-time and pile-up correction in gamma-ray spectrometry in INAA without distortion of the detector spectrum

Commercially available pulse generators for use in γ-ray spectroscopy to correct for dead-time and pile-up losses share the problem that the fall-time of the output pulses does not match the fall-time of the detector pulse. Upon pulse shaping in the main amplifier the pulser's signals result in a considerable undershoot of the amplifier's output signal, which cannot be restored by theP/Z network. As a result, peaks in the γ-ray spectrum are broadened. Moreover, amplitude stability of the generators is often poorer than the overall gain stability of the spectrometer. To overcome these problems a special pulse generator has been developed at the Interfaculty Reactor Institute, which simulates Ge-detector signals. It generates pulses with a constant frequency of 25 Hz using a crystal oscillator controlled mercury relay. The stability of the generator's amplitude and frequency is extremely high and the peak-shapes in the γ-ray spectrum are not distorted.

System performance of coherent transmission over cascaded in-line fiber amplifiers

The limitations of cascaded in-line amplifier systems using coherent modulation-demodulation schemes are discussed by evaluating the product of the data rate and the transmission distance in terms of three different aspects: linear ASE accumulation, fiber chromatic and polarization dispersion, and phase noise caused by ASE through the Kerr effect. The linear ASE accumulation is shown to make the maximum value of the data rate-distance product proportionally increase with the ratio of the amplifier output signal power to the noise figure. It is also shown that the Kerr-nonlinearity-induced phase noise limits the product of the data rate and the third power of the distance, the maximum value of which is inversely proportional to both the amplifier output signal power and the noise figure

Noise characteristics of Pr 3+ -doped fluoride fibre amplifier

The noise characteristics of a Pr3+-doped fluoride fibre amplifier (PDFFA) are reported for the first time. Using an amplifier with a 20 dB gain, a noise figure of 3.2 dB is obtained at a wavelength of 1.31 μm at an amplified output signal power between −18 and −2 dBm. However, it is observed that the noise figure increases when the signal wavelength is above l.32 μm.

Inline amplifier transmission experiments over 4500 km at 2.5 Gb/s

An inline amplifier system was constructed with erbium-doped fiber amplifiers spaced at 100 km and 80 km intervals. The system transmits 2.5 Gb/s signals over 2500 km with continuous-phase frequency-shift-keying heterodyne detection and over 4500 km with intensity-modulation direct detection. With respect to amplifier output signal power levels, it is experimentally shown that there exists a dynamic range within which long-distance signal transmission can be achieved with only small receiver sensitivity degradation. The range's upper and lower limits are determined by fiber nonlinearities and amplifier noise characteristics, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Apparatus for the transmission of speech

An apparatus for the transmission of speech, suitable for use in a hearing aid, has an acoustic input transducer followed by a controlled-gain broadband amplifier, which is followed by a parallel circuit of a number of frequency-selecting channels. The frequency-selecting channels divide the broadband output signal of the controlled-gain amplifier into a number of selected frequency channels. A threshold switch is included in each frequency-selecting channel. An acoustic output transducer is supplied with the sum of the output signals of the individual threshold switches.

Cross‐Talk in Bipolar Pacemakers

Investigation of dual chamber pacing and sensing interactions at high rates is becoming increasingly important with the advent of sensor driven dual chamber pacemakers. The present study was designed to investigate the pacemaker and lead interactions that will affect cross-talk during high rate atrial and ventricular pacing. The study was divided into two phases, phase one investigated the mechanisms of cross-talk using standard pacemaker circuitry and various electrode types in a canine model. In six dogs with complete heart block, dual chamber pacing was carried out with four lead types at increasing pacing rates, while output of the ventricular sense amplifier of a pacemaker breadboard was monitored. Ventricular sense amplifier output signals (n = 332) progressively increased from 31.5 +/- 18.3 mV at 100 ppm to 102 +/- 55 mV at 160 ppm. Smooth platinum-iridium and platinized leads were statistically different at higher pacing rates (P less than 0.05). This signal level is sufficient to lead to a ventricular sensing event. In a second phase of the study, the incidence of cross-talk at high pacing rates was studied in patients with implantable dual chamber bipolar pacemakers. In 166 clinical trials on 106 patients with the same pacemaker, there was evidence of cross-talk in 1/59 cases at 110 ppm and 3/47 at 130 ppm, but none at higher rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Optical emission spectroscopy of CF4+O2 plasmas using a new technique

Optical emission intensities in the sheath region are not the same as those in the plasma region. This is because not only the electron density, but also the electron temperature, is different between the two regions. In this study a Cu rod is inserted into the plasma, and the rod potential is altered from the ground potential to a negative potential with a frequency of 20 Hz. The optical emission ray comes from the sheath region when the negative potential is applied, but comes form the plasma region at the ground potential. We can immediately detect the difference of the emission intensities between the plasma and the sheath regions by a lock-in amplifier. The pre-amplifier is placed prior to the lock-in amplifier. By using this pre-amplifier the output signal of the lock-in amplifier can be adjusted to zero for any emission line. the emission spectra from a CF4+O2 plasma are measured. A small amount of Ar gas and/or N2 gas is added and the output signal of the lock-in amplifier is adjusted to zero for either the Ar emission line or the N2 emission line. In a fluorine-contained plasma the F emission intensity normalized by the Ar one has been widely used in order to obtain the F density. This validity is confirmed by the present experiment. It is also confirmed that the CO emission intensity normalized by that of N2 is proportional to the CO density. The metastable states play an important role in the optical emission intensities of CO and N2 molecules.

Automatic background noise suppression

A circuit for suppressing background noise of a continuous nature while enhancing speech signals, or signals having the transient temporal qualities of speech, includes a signal multiplier which, in the preferred embodiment, receives the composite audio signal along with a control signal present only when the speech component of the audio signal is present. The control signal may be derived from an AGC circuit having a slow attack, fast decay characteristic to establish a quiescent output level from the AGC amplifier in the absence of speech. An envelope detector is biased to provide a zero output amplitude in response to the quiescent amplifier output level. Speech components appearing in the amplifier output signal are then envelope-detected and filtered to provide the control signal. Alternatively, the control signal can be derived by envelope-detecting the audio signal, filtering the detected signal to remove its d.c. component representing the continuous noise, and then detecting and filtering again. In still another embodiment, the control signal acts upon a constant amplitude instead of the audio input signal in order to provide a speech-responsive tactile vibration for the deaf.

Measurement of erythrocyte velocity by use of a periodic differential detector.

An optical velocimeter employing a linear array of photodiodes has been developed and utilized for measuring erythrocyte velocities in the microcirculation. A magnified image of a microvessel is projected and aligned on a one-dimensional array of photodiodes. Photocurrent from odd-ordered diodes is summed, photocurrent from even-ordered diodes is summed, and a signal proportional to the difference between these two currents is produced by a differential amplifier. The center frequency of the output signal of the differential amplifier is proportional to the erythrocyte velocity. After lowpass filtering the output of the differential amplifier, a signal proportional to its frequency and therefore velocity is produced by a frequency-voltage converter. In vitro calibration with a moving dried smear of erythrocytes illustrated a linear relation between the output of the frequency-voltage converter and erythrocyte velocity for a wide range of velocities and magnifications. The system produces a stable zero output at zero velocity and had an estimated frequency response of greater than 40 Hz in vivo. Volumetric flow rates computed from velocity and diameter measurements at arteriolar bifurcations in the rat cremaster muscle were consistent with mass conservation.

Non-linear model for FET differential amplifier

A simple formula is presented for the relationship between an input differential voltage and the corresponding output differential current of an FET differential amplifier. Also, a closed-form expression is derived for the output signal of a differential amplifier excited by a multi-sinusoidal input signal.

Improved analysis of the harmonic and intermodulation performance of operational amplifiers

Simple formulas are presented for the nonlinear voltage-controlled current sources of operational amplifiers with strong inversion MOSFET, weak inversion MOSFET, JFET and bipolar input transistors, and are shown to fit the nonlinearities very well. Furthermore, closed-form expressions are derived for the output signal and intermodulation product levels of an operational amplifier excited by a multisinusoidal input signal. The results are presented in a form suitable for predicting the influence of the nonlinear voltage-controlled current source on the performance of electronic circuits incorporating operational amplifiers.

Echo ranging apparatus and method

Echo ranging apparatus to locate fish, vegetation and structure in the sea modifies signals presented to a recorder in the apparatus so as to enhance the capability of the user to distinguish fish in the vicinity of vegetation and structure, including the sea bed. A transducer receives the reflected echo signals. A receiver stage and amplifier stage present signals which, apart from the modification, would be conventionally useful in aiding the user to locate fish. However, a signal modifier connected at the output of the amplifier stage, between the amplifier stage and the input to the recorder, substantially enhances the capability of the apparatus. It does so by shunting signal reducer circuitry in parallel at the output of the amplifier when the level at the output surpasses a predetermined level, to reduce the signal levels at such output while retaining variations in such signal levels. Such retention, as opposed to, e.g., blanking out the output or setting the output to a fixed level, preserves information as to the source of the echoes which is present in such variations. By setting the triggering of the shunt connection at a high level corresponding to the echo from the sea bed, the sea bed will be indicated by a signal at a high level followed, after a time delay, by a steep reduction in level. Recordation of the information may be accomplished by providing the amplifier output signal, as modified, to the stylus of an electrochemical recorder, the stylus burning through a cover layer to a degree which depends on the level of the signal. With a graphite underlayer, and successive, straight, parallel traces along the paper, one per explorer pulse, the fish, vegetation and structure (including the sea bed) are shown on the recorder paper.

Loudspeaker protection circuit

A loudspeaker protection circuit senses an overload condition caused by an improper input signal or a fault within the amplifier by sensing a DC or infrasonic signal applied to the loudspeaker. The time between zero (axis) crossings of the amplifier output signal, which are related to the lower frequency components of the signal, are detected. If the period of time between zero crossings exceeds a predetermined time limit, the supply of the amplifier output signal to the loudspeaker is interrupted. In order to prevent false tripping of the circuit by normal conditions, the circuit only responds to signals exceeding a predetermined voltage level.

Frequency-Independent and Frequency-Dependent Nonlinear Models of TWT Amplifiers

Simple two-parameter formulas are presented for the functions involved in the amplitude-phase and the quadrature nonlinear models of a TWT amplifier, and are shown to fit measured data very well. Also, a closed-form expression is derived for the output signal of a TWT amplifier excited by two phase-modulated carriers, and an expression containing a single integral is given when more than two such earriers are involved. Finally, a frequencydependent quadrature model is proposed whose parameters are obtainable from single-tone measurements.

Continuously recording refractive index spectrograph for transparent and opaque insulators and semiconductors

An apparatus is described which enables the user to measure continuous refractive index spectra of opaque and transparent optically flat samples. The method of measurement is based on finding the Brewster's angle beta(B) of the sample. By modulating the angle of light incidence, the output signal of a lock-in amplifier, tuned to the modulation frequency, changes sign abruptly at beta(B). The lock-in signal is applied to a dc motor which drives a goniometer in that way that the sample is continually held at beta(B). Provided that the sample extinction coefficient k < or approximately 0.5, the accuracy of the refractive index measurements is better than 1%, or even 0.1% where k is approximately equal to 0.

Intermodulation Characteristics of X-Band IMPATT Amplifiers

The intermodulation products produced when two equal-amplitude signals are applied to the input of an X-band IMPATT-diode amplifier have been measured. An Si p+nn+ IMPATT diode was operated in a double-slug-tuned coaxial reflection amplifier circuit that was tuned to provide 20 dB of small-signal gain at 9.340 GHz. The intermodulation tests consist of measurements of the magnitudes and frequencies of the amplifier output signals as a function of the input-signal drive levels and frequency separations. The gain and single-frequency characteristics of the amplifer were also measured, and are used along with the theoretical device and circuit admittance characteristics as a basis for explanation of the intermodulation results. A low-frequency dominance mechanism is found to exist in which the low-frequency signals are amplifed more than the high-frequency signals. This mechanism becomes more significant as the amplifier drive level is increased.

A Pulse Shape Analyzer for Phoswich Detectors

An electronic technique for separating the signals from a phoswich detector is discussed. The preamp output signal is amplified by two double delay line amplifiers operating in parallel. The time difference between the crossover points of the two amplifier output signals is measured. This time difference is a function of the detector pulse shape. For small pulses, this technique has less time jitter than the more usual leading edge/crossover measurement. It is also less sensitive to control misadjustments. An instrument based on this principle is described.

Image Intensifier with Fiber Optics Plate and Image Orthicon Tube

When observing extremely fracturable specimens, such as organic compounds, clays and biological specimens by means of electron microscopy, it is very difficult to photograph the image of an object due to the very small current density of the irradiating electron beam. It is, therefore, desirable to use a high efficency image intensifier. The intensifiers presently used utilize Vidicon or Plumbicon camera tubes which exhibit comparatively low efficency. As a result, it is necessary to insert a photo-electron multiplier between the photo receiving surface and the surface of the camera tube. By so doing, the signal on the receiving surface is transformed into an amplified output signal, which involves considerably large shot noise arising from the collision of the photo-electron onto the electrodes or the fluorescent film in front of the second stage fiber optics plates.