Direct-coupled Amplifier Research Articles

A microstrip filter direct-coupled amplifier based on active coupling matrix synthesis

A microstrip filter direct-coupled amplifier based on active coupling matrix synthesis

Low Critical Temperature dc-SQUIDs for High Spatial Resolution Applications

We present the design and the performances of LTc SQUIDs with integrated micro pick-up coils to employ as magnetic field sensors in high spatial resolution measurements. The circular pick-up coils, having an inner diameter ranging from 5 to 50 mum and a line width of 2 mum, are well separated (1.5 mm) from the SQUID body to minimize magnetic interferences. The micro pick-up coils are connected to the SQUID by both magnetometer and gradiometric configurations. All SQUID types contain an integrated modulation/feedback coil for flux locked loop operations. At T = 4.2 K, the sensors have a measured white magnetic flux noise spectral density as low as 3 muPhi0/Hz1/2. These measurements were made in a flux locked loop, using a direct coupled amplifier, without the use of additional positive feedback. The low noise is attributed to the high intrinsic responsivity of our sensors. Finally, flux gain measurements (the ratio between the measured magnetic flux and the flux applied to the micro pick-up coil), are reported.

20 Gbit/s GaAs distributed direct-coupled amplifier

The authors describe advanced design techniques for direct-coupled amplifiers used in high speed optical communication systems. GaAs MESFET ICs designed with these techniques showed 1.5 times the bandwidth of conventional amplifiers and operated at a speed of 20 Gbit/s.

A 0-to-40-GHz direct-coupled distributed baseband amplifier IC with SCFL interface

We have developed a distributed baseband amplifier IC with a distributed source-coupled FET logic (SCFL) level transformer. The amplifier and the SCFL level transformer are directly coupled by a distributed level-shift circuit. The amplifier incorporates our new loss-compensation circuit to improve high-frequency performance. The IC, which was fabricated using commercially-available GaAs MESFET's has a gain of 5 dB and a 0-to-41-GHz bandwidth. It can also output a 40-Gbit/s pulse waveform on the SCFL logic level, so it can be directly coupled to an SCFL logic circuit. This is the highest performance among all reported GaAs MESFET baseband amplifiers with an SCFL interface.

A monolithic HEMT-HBT direct-coupled amplifier with active input matching

We have achieved the first active input matching of a monolithic microwave integrated circuit through the use of a common-gate (CG) HEMT directly coupled to the input of an HBT Darlington feedback amplifier. The HEMT and HBT devices were monolithically integrated on the same chip using selective MBE. This circuit features an active impedance match technique that eliminates the need for large microstrip matching components. The novel amplifier obtains greater than 10-dB gain over a DC-5 GHz band, a maximum IP3 of 27 dBm, and a minimum noise figure of 3.7 dB. In comparison with a HBT-only Darlington feedback design, the employment of the CG HEMT results in a 6-dB improvement in IP3 and a 1.5-2 dB reduction in noise figure. By adjusting the common-gate HEMT bias, the input return-loss can be tuned for near ideal 50 /spl Omega/ match (>20 dB). The actively matched HEMT-HBT amplifier demonstrates an active circuit technique, which can reduce the chip area and cost of HEMT-HBT MMICs while improving their performance.

A DC-10 GHz high gain-low noise GaAs HBT direct-coupled amplifier

An AlGaAs-GaAs HBT wideband low noise amplifier has been achieved using a direct-coupled amplifier topology. A nominal gain of 22.5 dB and a noise figure of 3.0-3.65 dB has been achieved over a DC-10 GHz band, while consuming less than 55 mW of DC power through a 5 V supply. This result benchmarks the lowest noise figure so far reported for a direct-coupled HBT amplifier at X-band frequencies. In addition, an approximate expression for the amplifier noise figure is given that predicts the noise figure to within 0.3 dB over bias and frequency. The amplifier can be compacted into a 0.3/spl times/0.3 mm/sup 2/ area and can yield as many as 30000 die per 3-in GaAs wafer. The broadband gain and noise figure, low DC power, and miniature die size makes this design attractive as a standard off-the-shelf microwave product for high volume commercial applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

40-GHz-bandwidth amplifier IC using AlGaAs/GaAs ballistic collection transistors with carbon-doped bases

An fmax of 192 GHz is achieved by a ballistic collection transistor with a launcher and a heavily carbon-doped base. A two-stage direct-coupled amplifier IC fabricated using the transistors provides a high gain of 16.8 dB with a 3 dB-down frequency of 40 GHz.

Design and performance of wideband GaAs MMIC's for high-speed optical communication systems

Advanced design techniques for GaAs wideband direct-coupled amplifiers are described. The amplifier achieved a 20 dB gain with a 3 dB bandwidth of 13 GHz and a 5-7 dB noise figure. An equalizing amplifier module consisting of amplifier and variable attenuator monolithic microwave integrated circuits (MMICs) exhibited a high gain of 43 dB over a 10 GHz band with a controllable gain of 20-43 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

10 GHz bandwidth, 20 dB gain low-noise direct-coupled amplifier ICs using Au/WSiN GaAs MESFET

A low-noise direct-coupled amplifier IC with a bandwidth of 10GHZ was developed using a 0.4 μm gate-length Au/WSiN GaAs MESFET technology. The amplifier achieved a high gain of 20 dB and a minimum noise figure of 3.2 dB with a power consumption of 365 mW.

Integrated amplifiers using fully ion-implanted InP JFETs with high transconductance

Monolithically integrated amplifiers have been fabricated using JFETs with a gate length of 1.5 mu m and a maximum transconductance of 110 mS/mm, the highest ever reported for ion-implanted InP JFETs. The amplifiers utilized both a conventional direct-coupled design and a new symmetrical design. The conventional direct-coupled amplifier shows a maximum gain of 8 (18 dB) while the symmetrical amplifier design exhibits the same gain without DC offset regardless of the FET threshold voltage and the power supply voltage used. >

A 3.2 GHz 26 dB wide-band monolithic matched GaAs MESFET feedback amplifier using cascodes

Feedback around cascode stages is demonstrated to be a useful means of making matched direct coupled amplifiers with higher bandwidths than afforded by conventional common-source topologies. Design techniques are described for an amplifier which is capable of operation to DC and which exhibits a measured gain of 26 dB, a 3.2 GHz bandwidth, and a 2.5:1 VSWR in a 1- mu m GaAs MESFET process. A novel adjustment scheme is introduced whereby the amplifier's frequency response can be modified using a DC bias voltage to ensure stable circuit operation in spite of MESFET modeling inaccuracies and GaAs processing variations. >

Application of AlGaAs/GaAs HBTs for wideband direct-coupled amplifiers

An AlGaAs/GaAs HBT direct-coupled amplifier has been designed and its characteristics described for the first time. The amplifier consists of two HBTs and three resistors without level-shift diodes. A superior amplifier performance of 11 dB gain with a 4 GHz bandwidth was obtained.

Design and Performance of Monolithic GaAs Direct-Coupled Preamplifiers and Main Amplifiers

The design and performance of a GaAs direct-coupled preamplifier and main amplifier is described. The amplifiers are fabricated by the self-aligned implantation for n/sup +/ -Iayer technology (SAINT) process. The developed preamplifiers have 13-dB gain, 3-GHz bandwidth, and 4.8-dB noise figure for the one-stage amplifier, and 22-dB gain, 2.7-GHz bandwidth, and 5.6-dB noise figure for the two-stage amplifier. The developed four-stage main amplifier has 36-dB gain and 1.5-GHz bandwidth with a power consumption of 710 mW. These amplifiers are promising candidates for application to high-speed data communication systems.

A monolithic direct-coupled GaAs IC amplifier with 12-GHz bandwidth

A two-stage feedback amplifier with direct connection between two stages has been developed for the 0.1-12-GHz frequency band. The measured gain is 10±1 dB with 2.5:1 input and 1.7:1 output VSWR. The measured minimum power output at 1-dB gain compression and maximum noise figure are 14 dBm and 9 dB, respectively, from 2 to 12 GHz. The chip size is less than 0.5 × 1.0 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and this area contains complete RF and bias circuitry. The amplifier also provides more than 25 dB of AGC capability.

A Monolithic Direct-Coupled GaAs Amplifier with 12-GHz Bandwidth

A two-stage feedback amplifier with direct connection between two stages has been developed for the 0.1- 12-GHz frequency band. The measured gain is 10+-1 dB with 2.5:1 input and 1.7:1 output VSWR. The measured minimum power output at 1-dB gain compression and maximum noise figure are 14 dBm and 9 dB, respectively, from 2 to 12 GHz. The chip size is less than 0.5 x 1.0 mm/sup 2/ and this area contains complete RF and bias circuitry. The amplifier also provides more than 25 dB of AGC capability.

New constant-current controlled astable multivibrator for generating sawtooth and square waves

This article presents a now constant-current controlled astable multivibrator in which only one resistor and one capacitor is used, the other elements being transistors. The circuit consists of a constant-current source and the multivibrator itself. The multivibrator is specifically designed to have a simple three-stage direct-coupled transistor amplifier, with the output of the third stage fed back to the first stage and a capacitor connected across any two collectors. The switching action takes place by means of that capacitor. Linear sawtooth and square waves are generated simultaneously at the transistor collectors. Since only one resistor and one capacitor are required, this circuit is practical with IC fabrication.

Ultra-broad-band GaAs monolithic direct-coupled feedback amplifiers

GaAs monolithic direct-coupled amplifiers with load resistor and feedback resistor have been developed. The fabricated amplifier using the self-aligned implantation for n+-layer technology (SAINT) FET's has a 10-dB gain, a 7.2-dB noise figure, and input VSWR less than 2.0 over the frequency range from dc to 4 GHz.

A Wideband Direct Coupled Amplifier Utilizing a Fast/Slow Loop Concept

A new direct coupled wideband amplifier, using thick film hybrid integrated circuit technology, has been designed and tested. A fast/slow loop configuration is used to provide a constant closed-loop voltage gain from dc to the closed-loop -3dB bandwidth of the fast stage. Analytical expressions are derived for the voltage transfer function. The risetime of the amplifier is < 2.5ns with < 10% overshoot for output signals to ± 5 volts into a 50-ohm load. The voltage gain can be varied from 2 to 10 while maintaining a constant 200MHz bandwidth. The measured dc drift was 27 ?V/0C referred to the input. Three hybridized amplifiers have been included in the implementation of a fast filter amplifier.

Monolithic GaAs direct-coupled amplifiers

Monolithic GaAs dc-coupled amplifiers with bandwidths up to 5 GHz are described. The multistage amplifiers include designs having 25-dB gain with 2-GHz bandwidth and 10-dB gain with 5-GHz bandwidth. Analysis of gain, bandwidth, and noise agrees with measurements. Distortion mechanisms are discussed, along with the performance of a low-distortion amplifier.

Comparative study of eye movements in the alert state and rapid eye movement sleep

Eye movements, in particular their speed during rapid eye movement (REM) sleep. were analyzed in five young normal subjects using electrooculography with a direct-coupled amplifier. Analysis was made mainly of horizontal movements. Eye movements were classified into two types by their velocity: those with speeds of more than 60° per second were categorized as rapid eye movements (REMs) and those with speeds of less than 60° slow eye movements. Comparisons between alert saccadic eye movements with a target, voluntary saccadic movements with lid closure, and REMs were made. The REMs were slower at all amplitudes of the eye movements.Two cases of left medial longitudinal fasciculus (MLF) syndrome were analyzed by the same method. They had the following eye movement characteristics during REM sleep: absence of adduction of the involved eye, disjugate movement, nystagmus-like movement in the eye contralateral to the eye affected by the MLF syndrome, convergence-like movements, and slow vertical movement mixed ...