Showing papers on "Amplifier published in 1996"

Circuit techniques for reducing the effects of op-amp imperfections: autozeroing, correlated double sampling, and chopper stabilization

Abstract: In linear IC's fabricated in a low-voltage CMOS technology, the reduction of the dynamic range due to the dc offset and low frequency noise of the amplifiers becomes increasingly significant. Also, the achievable amplifier gain is often quite low in such a technology, since cascoding may not be a practical circuit option due to the resulting reduction of the output signal swing. In this paper, some old and some new circuit techniques are described for the compensation of the amplifier's most important nonideal effects including the noise (mainly thermal and 1/f noise), the input-referred dc offset voltage as well as the finite gain resulting in a nonideal virtual ground at the input.

Optoelectronic microwave oscillator

Abstract: We describe a novel oscillator that converts continuous light energy into stable and spectrally pure microwave signals. This optoelectronic microwave oscillator consists of a pump laser and a feedback circuit including an intensity modulator, an optical fiber delay line, a photodetector, an amplifier, and a filter. We develop a quasi-linear theory and obtain expressions for the threshold condition, the amplitude, the frequency, the line width, and the spectral power density of the oscillation. We also present experimental data to compare with the theoretical results. Our findings indicate that the optoelectronic microwave oscillator can generate ultrastable, spectrally pure microwave reference signals up to 75 GHz with a phase noise lower than -140 dBc/Hz at 10 kHz.

Control apparatus for electrosurgical generator power output

Abstract: A power control apparatus for an electrosurgical generator (10) is used for controlling output power from the generator (10) to the tissue or bodily fluids of a patient (11). The control apparatus rapidly determines the range of impedance of the load on the electrosurgical generator (10) and adjusts the output power accordingly. Output current and output voltage from the electrosurgical generator (10) are monitored and sent to a microprocessor (18). The microprocessor (18) runs an algorithm that rapidly determines the impedance range of the load on the generator (10). The algorithm uses computational techniques, such as comparisons and bit shifting, that avoid long division and other time-consuming operations. The microprocessor (18) can then adjust a high voltage power supply (15) that effects the radio frequency amplifier stage. A method for controlling the power of the electrosurgical generator (10), including steps in the algorithm, is also disclosed.

Digital waveform generation for electrosurgical generators

Abstract: An electrosurgical generator (10) has an improved design for generating output waveforms using a microprocessor (15). The waveforms are generated in the form of a serial digital output from the microprocessor (15). The serial digital output is transformed into an electrosurgical RF output in an amplifier stage. The improved design also includes a monitoring circuit to continuously monitor the serial digital output by time-averaging the output, and then comparing that value with a threshold. The electrosurgical generator (10) comprises a microprocessor (15), an algorithm in the microprocessor (15) capable of toggling an output port of the microprocessor (15), an output amplifier (16), an adjustable high voltage DC power supply (17), a patient circuit including an active electrode (12) and a return electrode (13). The electrosurgical generator (10) may further comprise a mode selector (20) for selecting one of a plurality of pulse patterns in the serial digital output, and a plurality of command sequences in the algorithm, where each command sequence is designed to produce one of the plurality of patterns. There may also be a tank damp circuit (22) for reducing the amplitude of voltage spikes in the electrosurgical output, and a pulse suppression circuit. The monitoring circuit comprises a low pass filter (19) and a comparator to verify operation of the waveform generator.

A 1.5 V, 1.5 GHz CMOS low noise amplifier

Abstract: A 1.5 GHz low noise amplifier for a Global Positioning System (GPS) receiver has been implemented in a 0.6 /spl mu/m CMOS process. This amplifier provides a forward gain of 22 dB with a noise figure of only 3.5 dB while drawing 30 mW from a 1.5 V supply. To the authors' knowledge, this represents the lowest noise figure reported to date for a CMOS amplifier operating above 1 GHz.

Long-period fiber-grating-based gain equalizers.

Abstract: Long-period fiber gratings are used to flatten the gain spectrum of erbium-doped fiber amplifiers. A broadband amplifier with <0.2-dB gain variation over 30 nm is presented. We also show that a chain of amplifiers can be equalized, leading to a bandwidth enhancement by a factor of 3.

A 1 GHz CMOS RF front-end IC for a direct-conversion wireless receiver

Abstract: An integrated low-noise amplifier and downconversion mixer operating at 1 GHz has been fabricated for the first time in 1 /spl mu/m CMOS. The overall conversion gain is almost 20 dB, the double-sideband noise figure is 3.2 dB, the IIP3 is +8 dBm, and the circuit takes 9 mA from a 3 V supply. Circuit design methods which exploit the features of CMOS well suited to these functions are in large part responsible for this performance. The front-end is also characterized in several other ways relevant to direct-conversion receivers.

A 2.7 V 900 MHz CMOS LNA and mixer

Abstract: A CMOS low-noise amplifier (LNA) and a mixer for RF front-end applications are described. A current reuse technique is described that increases amplifier transconductance for the LNA and mixer without increasing power dissipation, compared to standard topologies. At 900 MHz, the LNA minimum noise figure (NF) is 1.9 dB, input third-order intercept point (IIP3) is -3.2 dBm and forward gain is 15.6 dB. With a 1-GHz local oscillator (LO) and a 900-MHz RF input, the mixer minimum double sideband noise figure (DSB NF) is 5.8 dB, IIP3 is -4.1 dBm, and power conversion gain is 8.8 dB. The LNA and mixer, respectively, consume 20 mW and 7 mW from a 2.7 V power supply. The active areas of the LNA and mixer are 0.7 mm/spl times/0.4 mm and 0.7 mm/spl times/0.2 mm, respectively. The prototypes were fabricated in a 0.5-/spl mu/m CMOS process.

Radio frequency energy delivery system for multipolar electrode catheters

Abstract: A radio-frequency ablation system is disclosed in which the power, voltage, or temperature delivered to multiple electrodes may be dynamically controlled, and in which the electrodes may be simultaneously energized in phase with each other to achieve a desired lesion pattern. The system comprises a multiple electrode ablation catheter, each electrode having a temperature sensor operatively associated therewith. Each electrode is energized by its own RF amplifier, and all of the electrodes are driven in phase with each other by a common sine wave oscillator. A feedback network controls the degree of amplification of the separate RF amplifiers. According to a further aspect of the invention, a modular power supply arrangement is disclosed which is configurable to dynamically control the power, voltage, or temperature delivered to multiple electrodes of a multipolar ablation device. An arbitrary number of electrodes may be simultaneously energized in phase with each other to achieve a desired lesion pattern using the modular power supply by providing a sufficient number of removable modules.

Net optical gain at 1.53 mu m in Er-doped Al2O3 waveguides on silicon

Abstract: A 4 cm long Er‐doped Al2O3 spiral waveguide amplifier was fabricated on a Si substrate, and integrated with wavelength division multiplexers within a total area of 15 mm2. When pumped with 9 mW 1.48 μm light from a laser diode, the amplifier shows 2.3 dB net optical gain at 1.53 μm. The gain threshold was 3 mW. The amplifier was doped with Er by ion implantation to a concentration of 2.7×1020 cm−3. The data agree well with calculations based on a model which includes the effects of cooperative upconversion and excited state absorption. For an optimized amplifier, net optical gain of 20 dB is predicted.

Semiconductor amplifiers and lasers with tapered gain regions

Abstract: Semiconductor amplifiers and lasers with tapered gain regions provide the highest-brightness all-semiconductor sources of near infrared continuous wave (CW) power and have many useful applications. Simple models of these devices are described. Their applications, device performance and brightness limitations are reviewed1.

Intermodulation distortion in Kahn-technique transmitters

Abstract: The Kahn Envelope Elimination and Restoration (EER) technique implements a linear RF power amplifier (PA) by combining nonlinear, but efficient, RF and AF power amplifiers. For signals with high peak-to-average ratios, the average efficiency of a Kahn-technique transmitter can be three to four times that of a transmitter that employs conventional linear RP PAs. Since switching-mode amplifiers are employed, the linearity of an EER transmitter depends upon parameters such as the bandwidth of the envelope modulator and the differential delay between envelope and phase signals. This paper determines the relationship between these parameters and IMD levels and verifies the predictions by laboratory measurements. The results can be used to determine the requirements for the components of a Kahn-technique transmitter.

Electrical Engineering: Principles and Applications

Abstract: (NOTE: Each chapter concludes with Summary and Problems.) I. CIRCUITS. 1. Introduction. Overview of Electrical Engineering. Circuits, Currents, and Voltages. Power and Energy. Kirchhoff's Current Law. Kirchhoff's Voltage Law. Introduction to Circuit Elements. Introduction to Circuits. 2. Resistive Circuits. Resistances in Series and Parallel. Network Analysis by Using Series and Parallel Equivalents. Voltage-Divider and Current-Divider Circuits. Node-Voltage Analysis. Mesh-Current Analysis. Thevenin and Norton Equivalent Circuits. Superposition Principle. Wheatstone Bridge. 3. Inductance and Capacitance. Capacitance. Capacitances in Series and Parallel. Physical Characteristics of Capacitors. Inductance. Inductances in Series and Parallel. Practical Inductors. Mutual Inductance. 4. Transients. First-Order RC Circuits. DC Steady State. RL Circuits. RC and RL Circuits with General Sources. Second-Order Circuits. 5. Steady-State Sinusoidal Analysis. Sinusoidal Currents and Voltages. Phasors. Complex Impedances. Circuit Analysis with Phasors and Complex Impedances. Power in AC Circuits. Thevenin and Norton Equivalent Circuits. Balanced Three-Phase Circuits. 6. Frequency Response, Bode Plots, and Resonance. Fourier Analysis, Filters, and Transfer Functions. First-Order Lowpass Filters. Decibels, the Cascade Connection, and Logarithmic Frequency Scales. Bode Plots. First-Order Highpass Filters. Series Resonance. Parallel Resonance. Ideal and Second-Order Filters. Digital Signal Processing. II. DIGITAL SYSTEMS. 7. Logic Circuits. Basic Logic Circuit Concepts. Representation of Numerical Data in Binary Form. Combinatorial Logic Circuits. Synthesis of Logic Circuits. Minimization of Logic Circuits. Sequential Logic Circuits. 8. Microcomputers. Computer Organization. Memory Types. Digital Process Control. The Motorola 68HC11/12. The Instruction Set and Addressing Modes for the 68HC11. Assembly-Language Programming. 9. Computer-Based Instrumentation Systems. Measurement Concepts and Sensors. Signal Conditioning. Analog-to-Digital Conversion. LabVIEWaA A . III. ELECTRONICS. 10. Diodes. Basic Diode Concepts. Load-Line Analysis of Diode Circuits. Zener-Diode Voltage-Regulator Circuits. Ideal-Diode Model. Piecewise-Linear Diode Models. Rectifier Circuits. Wave-Shaping Circuits. Linear Small-Signal Equivalent Circuits. 11. Amplifiers: Specifications and External Characteristics. Basic Amplifier Concepts. Cascaded Amplifiers. Power Supplies and Efficiency. Additional Amplifier Models. Importance of Amplifier Impedances in Various Applications. Ideal Amplifiers. Frequency Response. Linear Waveform Distortion. Pulse Response. Transfer Characteristic and Nonlinear Distortion. Differential Amplifiers. Offset Voltage, Bias Current, and Offset Current. 12. Field-Effect Transistors. NMOS and PMOS Transistors. Load-Line Analysis of a Simple NMOS Amplifier. Bias Circuits. Small-Signal Equivalent Circuits. Common-Source Amplifiers. Source Followers. CMOS Logic Gates. 13. Bipolar Junction Transistors. Current and Voltage Relationships. Common-Emitter Characteristics. Load-Line Analysis of a Common-Emitter Amplifier. pnp Bipolar Junction Transistor. Large-Signal DC Circuit Models. Large-Signal DC Analysis of BJT Circuits. Small-Signal Equivalent Circuits. Common-Emitter Amplifiers. Emitter-Followers. 14. Operational Amplifiers. Ideal Operational Amplifiers. Summing-Point Constraint. Inverting Amplifiers. Noninverting Amplifiers. Design of Simple Amplifiers. Op-Amp Imperfections in the Linear Range of Operation. Nonlinear Limitations. DC Imperfections. Differential and Instrumentation Amplifiers. Integrators and Differentiators. Active Filters. IV. ELECTROMECHANICS. 15. Magnetic Circuits and Transformers. Magnetic Fields. Magnetic Circuits. Inductance and Mutual Inductance. Magnetic Materials. Ideal Transformers. Real Transformers. 16. DC Machines. Overview of Motors. Principles of DC Machines. Rotating DC Machines. Shunt-Connected and Separately Excited DC Motors. Series-Connected DC Motors. Speed Control of DC Motors. 17. AC Machines. Three-Phase Induction Motors. Equivalent Circuit and Performance Calculations for Induction Motors. Synchronous Machines. Single-Phase Motors. Stepper Motors. Appendix A: Complex Numbers. Appendix B: Nominal Values and the Color Code for Resistors. Appendix C: Preparing for the Fundamentals of Engineering Exam. Appendix D: Computer-Aided Circuit Analysis. Index.

Transmission and reception apparatus having a single phase-locked loop and method thereof

Abstract: A transmission and reception method and apparatus is capable of supplying local oscillation frequencies for upconversion and downconversion, as well as carrier frequencies for modulation and demodulation by utilizing only one local oscillator The apparatus includes a reference signal generator for generating a reference signal, and a phase locked loop for locking the output of the reference signal generator to a predetermined frequency A signal generator generates a signal in response to the output provided from the phase locked loop, and provides the signal to phase shifters in modulation and demodulation circuits A first frequency multiplier multiplies the output of the signal generator, a first band pass filter band pass filters the output of the first frequency multiplier, and a first amplifier amplifies the output of the first band pass filter and provides the amplified result to an upconversion mixer A second frequency multiplier multiplies the output of the signal generator, a second band pass filter band pass filters the output of the second frequency multiplier, and a second amplifier amplifies the output of the second band pass filter and provides the amplified result to a downconversion mixer

Applications of the current feedback operational amplifiers

Abstract: The current feedback operational amplifiers (CFOAs) are receiving increasing attention as basic building blocks in analog circuit design. This paper gives an overview of the applications of the CFOAs, in particular several new circuits employing the CFOA as the active element are given. These circuits include differential voltage amplifiers, differential integrators, nonideal and ideal inductors, frequency dependent negative resistors and filters. The advantages of using the CFOAs in realizing low sensitivity universal filters with grounded elements will be demonstrated by several new circuits suitable for VLSI implementation. PSPICE simulations using the AD844-CFOA which indicate the frequency limitations of some of the proposed circuits are included.

Energy Extraction and Achievement of the Saturation Limit in a Discharge-Pumped Table-Top Soft X-Ray Amplifier.

Abstract: We report the generation of laser pulse energies up to $30\ensuremath{\mu}\mathrm{J}$ at 46.9 nm in the plasma column of a fast compressional capillary discharge. Double pass experiments using an iridium mirror achieved a gain-length product greater than 25. The results provide the first clear evidence of saturated operation of a table-top soft x-ray amplifier.

Wavelength division multiplexing in long-haul transmission systems

Abstract: Wavelength division multiplexing shows great promise for the next generation of long-haul undersea cable transmission systems. WDM techniques will allow for greater transmission capacity and network flexibility compared to the present single-channel optical amplifier systems. The transmission of many WDM channels over transoceanic distances can be limited by a variety of phenomena, including the finite bandwidth of the erbium-doped fiber amplifier repeaters, the nonlinear interactions between channels, and the noise accumulation along the chain of amplifiers. Significant progress has been made over the past few years in understanding the nature of these impairments for long-distance transmission. This paper describes techniques used to transmit many WDM channels over transoceanic distances using the nonreturn-to-zero format and other nonsoliton methods. Data is presented for several WDM experiments including the transmission of 100 Gb/s (20 channels of 5 Gb/s) over 9100 km.

Solid-state image sensor with focal-plane digital photon-counting pixel array

Abstract: A solid-state focal-plane imaging system comprises an N×N array of high gain, low-noise unit cells, each unit cell being connected to a different one of photovoltaic detector diodes, one for each unit cell, interspersed in the array for ultralow level image detection and a plurality of digital counters coupled to the outputs of the unit cell by a multiplexer (either a separate counter for each unit cell or a row of N of counters time shared with N rows of digital counters). Each unit cell includes two self-biasing cascode amplifiers in cascade for a high charge-to-voltage conversion gain (>1 mV/e - ) and an electronic switch to reset input capacitance to a reference potential in order to be able to discriminate detection of an incident photon by the photoelectron (e - ) generated in the detector diode at the input of the first cascode amplifier in order to count incident photons individually in a digital counter connected to the output of the second cascode amplifier. Reseting the input capacitance and initiating self-biasing of the amplifiers occurs every clock cycle of an integratng period to enable ultralow light level image detection by the array of photovoltaic detector diodes under such ultralow light level conditions that the photon flux will statistically provide only a single photon at a time incident on any one detector diode during any clock cycle.

Optical amplifier with high energy levels systems providing high peak powers

Abstract: Two approaches are provided for achieving an optical amplifier system capable of producing high peak power, high energy pulse outputs while suppressing scattering noise The first approach relates to an optical amplifier system which has at least one laser diode pulsed or cw pumped double clad fiber amplifier utilized for receiving a high frequency modulated injected signal pulse of short duration from the laser diode, via the fiber core, for amplification by coupling pump light into the inner cladding of the fiber The average signal power is sufficient to saturate the gain of the fiber so as to minimize significant onset and buildup of forward and backward scattering noise The duty cycle of the injected signal source pulse is chosen to allow adequate gain recovery in the fiber amplifier between pulses The second approach relates to a cascaded optical amplifier system having at least two optical amplifying stages with two pulsed pump sources providing and two amplifying media, the first of which receives the injection and at least one pump signal wherein the injection pulsed signal is amplified to a first power and energy level The second amplifying medium, optically coupled to the first, amplifies the first level signal to a second level amplified, injection pulsed signal The duty cycle of the injection pulsed optical signal is synchronized with the first and second pulsed pump signals with the first pulsed pump signal having a different duration in the duty cycle than the second pulsed pump signal

CMOS low-distortion high-frequency variable-gain amplifier

Abstract: The overall system performance of mixed-signal CMOS IC's is largely determined by the dynamic performance of the analog front-ends. System features are, in contrast, mainly set by the digital architecture. In order to optimize the dynamic range of the system and to minimize the sensitivity to substrate noise, the analog-to-digital converter (ADC) has to be preceded by a variable-gain amplifier (VGA) and a differential circuit topology for the complete front-end to be adopted. Since most of present-day applications are based on single-sided signal source definitions, the differential-input VGA must be able to perform a single-to-differential signal conversion. This paper describes the principle and design of a differential CMOS low-distortion variable-gain amplifier for high-frequency (video) applications. Experimental results of the circuit show total harmonic distortion figures better than -60 dB and a gain accuracy of 0.05 dB over the -2 to +12 dB gain range for single-sided input signals.

High-frequency amplifier, transmitting device and receiving device

Abstract: A radio frequency amplifier, for amplifying a radio frequency signal, comprises a plurality of active element groups, each comprising one or more active elements for amplifying a signal, with input terminals of said one or more active elements being combined to form a single input terminal and output terminals of said one or more active elements being combined to form a single output terminal and bias control means for controlling bias conditions of said plurality of active element groups arranged in such a manner that at low power output deterioration of the gain and distortion characteristics of the amplifier is avoided and sufficiently low power consumption can be achieved by switching the bias voltages of each of the active element groups of the high-frequency amplifier individually between an operating voltage and an off voltage.

Digital signal processing for linearization of small input signals to a tri-state power switch

Abstract: An all digital switching amplifier includes an input over-sampling filter (20) for receiving a pulse code modulated (PCM) digital input signal. Oversampled PCM data are supplied to a multibit noise shaper (22), which frequency shapes quantization error. The oversampled, noise-shaped, PCM data is applied to an amplitude-to-time converter (24), which produces variable-width command pulses. The command pulses from converter (24) are applied to switch drive logic circuit (28) to enable switches (26) to connect a filter (30) and load (32) to power supply (34).

Hybrid short-pulse amplifiers with phase-mismatch compensated pulse stretchers and compressors

Abstract: Disclosed is a system for amplification of ultrashort optical pulses. The disclosed system has reduced size and increased robustness, reliability and cost-effectiveness. The disclosed invention is particularly effective in chirped pulse amplification (CPA) systems wherein pulses are stretched, amplified, and re-compressed. According to one aspect of the invention a compact stretcher is used with a bulk compressor, and compatibility between them is achieved by inserting a telescope in the path of the collimated beam. Alternatively, compatibility between the stretcher and the compressor is achieved by creating nonlinearly chirped bragg grating in the fiber stretcher. According to another aspect of the invention, a fiber and a bulk amplifiers are used to amplify the pulse, and compatibility between them is achieved by inserting a doubling crystal in the path of the pulse between the two amplifiers. Another aspect of the disclosed amplification system is the pumping of a laser amplifier with a laser pump of the same material as the laser amplifier, but operating under different conditions.

Adaptive digital predistorter for power amplifiers with real time modeling of memoryless complex gains

Abstract: When the signals resulting from linear modulation methods, like M-ary QAM, are passed through a nonlinear power amplifier, their fluctuating envelope causes distortion and spectral spreading. In order to avoid these effects, while maintaining both power and spectral efficiency, the use of linearization techniques is necessary. This paper presents a digital predistorter with real time modeling of AM-AM and AM-PM characteristics of a power amplifier (PA). The input and output lowpass equivalent complex envelopes of the amplifier are sampled, scaled and updated into a lookup table to provide the predistorted signal. An improvement of 45 dB of out-of-band power is obtained when simulating with Signal Processing WorkSystem (SPW). The proposed technique is robust and efficient since no iterative procedure is needed, hence the convergence time is eliminated.

Efficient AC and noise analysis of two-tone RF circuits

Abstract: In this paper we present a preconditioned recycled Krylov-subspace method to accelerate a recently developed approach for ac and noise analysis of linear periodically-varying communication circuits. Examples are given to show that the combined method can be used to analyse switching filter frequency response, mixer 1/f noise frequency translation, and amplifier intermodulation distortion. In addition, it is shown that for large circuits the preconditioned recycled Krylov-subspace method is up to forty times faster than the standard optimized direct methods.

Method and apparatus for controlling peak factor of coherent frequency-division-multiplexed systems

Abstract: A system is disclosed which can measure and control the absolute phase angles of individual coherent Frequency-Division-Multiplexed (FDM) carriers which have been combined to form a composite signal. User-specified phase relationships for the carriers are predetermined to produce an optimum peak factor (peak power to average power ratio) of the composite signal for a given application. In the preferred embodiment, phase relationships chosen to minimize peak factor can dramatically reduce the presence of intermodulation distortion products which can be detrimental to present communication architectures, such as Community Antenna Television (CATV). As CATV providers move toward using fiber-optic transmission networks for support of larger customer bases and inclusion of digital channels, there is a greater risk for rising signal amplitudes to induce clipping of CATV laser transmitters, thereby creating distortion which degrades analog picture quality and causes digital transmission errors to exceed maximum thresholds. Higher peak factors may be desirable, however, when testing individual components including CATV amplifiers, or subsystems such as linear fiber-optic transmission equipment, in order to more accurately characterize field performance. The disclosed invention uses a combination of RF, baseband, and digital techniques to repeatedly acquire and maintain desired peak factor conditions within coherent FDM systems.

RF and Microwave Circuit Design for Wireless Communications

Abstract: From the Publisher: RF and Microwave Circuit Design for Wireless Communications addresses the complicated modulation schemes and higher frequencies required of today's wireless communications circuits. Covering cutting-edge developments in mixer circuits, frequency synthesizers, amplifier design, noise, and the future of wireless communication, it helps you design applications for digital cellular telephony, wireless LANs, PCS, GaAs and high-speed silicon bipolar IC technology, and low-power RF circuit technology.

Writable analog reference voltage storage device

Abstract: A circuit for generating N analog voltage signals for reference or bias use employs N analog floating gate storage devices. Circuitry is provided so that all floating gate storage devices can be programmed to their target voltages individually or in parallel. Electron injection circuitry is provided for injecting electrons on to and a tunneling structure is provided for removing electrons from the floating gate of each floating gate storage device. A transistor structure with a lightly doped drain is provided for control of the tunneling structure. A capacitor is connected to each floating gate node to provide control of the injection structure. A dynamic analog storage element is provided to store the target voltage for the floating gate storage device. A comparator is provided to monitor the floating gate voltage and target voltage and control tunneling and injection. A digital storage device is provided to statically store the output of the comparator. During normal operation of the voltage reference circuit, the voltage comparator is configured as a follower amplifier to buffer the analog voltage output. During normal operation of the bias reference circuit, the current comparator is configured as a current mirror to buffer the analog current output.

Femtosecond self- and cross-phase modulation in semiconductor laser amplifiers

Abstract: We present detailed derivation of our new model for femtosecond pulse amplification in semiconductor laser amplifiers. The various dynamic nonlinear terms of gain compression and associated self-phase modulation are derived semiphenomenologically, and are discussed physically. Included are the effects of carrier depletion, carrier heating and spectral hole-burning, as well as linear and two photon absorption and the instantaneous nonlinear index. Additionally, we account for dynamically changing gain curvature and slope. We apply the theory to strong signal cross-phase-cross-gain modulation experiments with /spl sim/500 fs pulses in a broad area GaAs amplifier and show that the model accurately describes the observed complex phenomena. We also present experimental results on single beam strong signal amplification in two different quantum-well amplifiers using 150-200 fs duration pulses. For such pulse lengths, carrier heating becomes an integrating nonlinearity and its self-phase modulation is similar to that due to carrier depletion. Additionally, since the pulse spectrum is broad, the gain slope and curvature shift and narrow it. The resultant spectral distortions are very different than observed (and modeled) earlier for the /spl sim/500 fs pulses. The model is again able to correctly describe the evolution of these ultrashort pulses, indicating that it remains valid, even though pulse durations approach the intraband relaxation time.

Low-power CMOS continuous-time filters

Abstract: A design technique for low-power continuous-time filters using digital CMOS technology is presented The basic building block is a fully-balanced integrator with its unity-gain frequency determined by a small-signal transconductance and MOSFET gate capacitance Integrator excess phase shift is reduced using balanced signal paths, and open-loop gain is increased using low-voltage cascode amplifiers Two-pole bandpass and five-pole lowpass ladder filters have been implemented in a 12 /spl mu/m n-well CMOS process The lowpass prototypes provided 300 kHz-1000 kHz bias-current-tunable -3 dB bandwidth, 67 dB dynamic range with 1% total harmonic distortion (THD), and 30 /spl mu/W/pole (300 kHz bandwidth) power dissipation with a 15 V supply; the bandpass prototypes had a tunable center frequency of 300 kHz-1000 kHz, Q of 85, and power dissipation of 75 /spl mu/W/pole (525 kHz center frequency) from a 15 V supply The active filter area was 01 mm/sup 2//pole for both designs