Parasitic Circuit Research Articles

Integrable analogue active filters for implementation in MOS technology

A design method for MOS-compatible analogue active filters that use only integrating amplifiers and ratios of capacitors is discussed. The circuits retain most of the implementation advantages of sampled-data switched-capacitor filters, but are complementary to switched-capacitor filters in providing better and more predictable performance at high frequencies. The effects of circuit parasitics and amplifier nonidealities are discussed and experimental results are presented to illustrate the performance.

An EBS (electron bombarded semiconductor) high-current pulse amplifier

An EBS (electron bombarded semiconductor) pulse amplifier which generates high-current fast-risetime variable-width pulses into low impedance loads is described. Current pulses of 100 A into a 1-Ω load have been obtained with a risetime of 2.2 ns. A di/dt of 40 000 A/µs and a dV/dt of 71 000 V/µs have been obtained. Pulse lengths to 1 µs at 0.1-percent duty have been achieved. The risetime and peak current capabilities are presently limited by internal circuit parasitics. Without parasistics, the theoretical peak output capabilities for this EBS are 340 A with a di/dt of 6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> A/µs.

Characterization of IMPATT diodes at millimeter-wave frequencies

In order to evaluate the quality of a microwave device and to design a suitable circuit for it, the device must be characterized in terms of an equivalent circuit. At low microwave frequencies L through X bands, devices can be characterized in a relatively simple manner in conjunction with a coaxial transmission line network analyzer. At higher frequencies, such as millimeter-wave frequencies, however, the characterization must be carried out in a waveguide. This paper presents a technique for characterizing an IMPATT diode mounted in a waveguide and the associated circuit parasitics at millimeter-wave frequencies. The passive and active device parameters and the circuit parasitics, which have increased effects particularly at millimeter-wave frequencies, are evaluated by means of a computer-aided iterative curve-fitting method from the measured variation of the input impedance (VSWR) as a function of position of a movable short placed behind the device. The accuracy of the technique and the computer program are first checked by comparing the characteristics of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</tex> -band IMPATT diode measured by the present technique and those measured by the network analyzer method. The characterization of a millimeter-wave IMPATT diode is then presented. A technique to achieve the stabilization required for the measurement of active parameters of the diode is also described. Comparison of the performance of an IMPATT diode amplifier calculated from the measured diode characteristics with the experimentally observed amplifier performance is then presented. It is shown that the device characterization technique can effectively be used for the analysis and design of a millimeter-wave circuit in which the device is used.

Abnormal arteriovenous communications. Great variability of effects with particular reference to delayed development of cardiac failure.

Clinical experiences and experimental studies provide evidence that an abnormal communication between the arterial and venous systems introduces into the circulation two circuits of flowing blood, one characterized by high arterial pressure and high peripheral resistance, and a second system bypassing part of the first, thus introducing a shorter circuit back to the heart, characterized by low pressure and low resistance, each supplied with flowing blood from the same central source, the heart. This shorter circuit acts solely as a parasitic circuit engrafted upon the normal circulation, serving no useful purpose, but capable of producing serious deleterious effects, depending upon the volume of blood diverted from the normal circulation into the shorter or parasitic circuit. Intimately dependent upon this diversion of differing volumes of blood into the shorter circuit is the great diversity in the effects of a peripheral fistula upon the heart: the complete absence of cardiac dilatation in some cases; the rapid development of cardiac dilatation and cardiac failure within 2½ months as exemplified in Mason's case; and the long delay of 57 years in the development of cardiac failure as observed by Dorney. Due to the high pressure in the normal circuit and the low resistance in the fistula circuit, there is a constant tendency for blood to be diverted or sequestered, as it were, in the fistulous or parasitic circuit, the factors determining the volume of blood so diverted being the size of the fistula and the distensibility of its rim or border, this, in turn, being dependent upon the character of the fibrous tissue deposited around the fistula in the course of healing. Firm, rigid, and excessive scarring permits only a small volume of blood to be sequestered in the fistula circuit, dilating only mildly the components of the parasitic circuit, whereas an elastic and distensible fistulous border permits progressive expansion of the fistulous opening with a progressive increase in the volume of blood sequestered in the fistula circuit, causing progressive dilatation of all components of this circuit including the four chambers of the heart, the aorta and artery proximal to the fistula, the fistula itself, the proximal vein, the vena cava, and the pulmonary vascular bed. All gradations in distensibility of the fistula may occur, and hence all gradations in cardiac dilatation will occur. Also, all gradations in the rapidity of fistulous expansion may occur and, therefore, all gradations in rapidity of cardiac dilatation will occur. This concept of a progressive expansion of a fistula of slow or rapid development permitting more and more blood to be shunted or sequestered in a shorter parasitic circuit at very rapid or very slow rates of increase provides the long-sought explanation of the rapid or long-delayed development of cardiac dilatation and failure in the presence of a peripheral fistula. It is suggested that the same explanation is applicable to the effects of all abnormal arteriovenous communications, including intracardiac shunts and even some hemangiomata, since all are subject to the same hydrodynamic law that flowing blood like flowing water seeks the path of least resistance.

Methods of isolation of active elements in integrated circuits

Two basic techniques for the isolation of active elements within a monolithic silicon planar integrated circuit are described. The first method consists of placing back-biased silicon diodes between each active element. The high impedance of the silicon junction below breakdown voltage acts as the isolating element. This impedance is frequency dependent, since the junction has a parasitic capacitance associated with it. This parasitic capacitance limits circuit performance at very high frequencies. The second method of isolation involves forming the active elements within a high resistivity silicon substrate. The high sheet resistance of the substrate is used to form regions of high impedance between the active elements. This impedance is not frequency dependent and circuit performance at high frequencies is not limited by this isolation scheme.

Microwave Operation of Drift Transistors in Transit-Time Mode

The transit-time transistor and its operation was first proposed by Weinreich <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">^1</tex> in relation to a diffusion transistor. The similarity to the diffusion-delay diode and the existence of a negative resistance has been pointed out in accord with the original theoretical work by Shockley <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">^2</tex> . In this paper the drift transistor is analyzed in respect to transit-time effects of minority carriers across the base region, which appear at frequencies above the normal cutoff frequency and are more favorable than in a diffusion transistor due to larger excess phase shifts in the base transport factor. Amplification and power-generation properties at frequencies properly related to the base transit time are theoretically predicted and lie within frequency bands above the cutoff frequency. Experimental vertification of gain and power have been obtained with some commercial and developmental high-frequency mesa-type drift transistors. The results are reported, together with the special microwave circuitry utilized in the experiments. Although realization of gain and power in the microwave region with present transistor encapsulations encounters difficulties in the form of parasitic circuit elements, e.g., lead inductances, and interelectrode capacities, a promising application of suitably designed and packaged drift transistors in the microwave-frequency region will be demonstrated. The operation of the drift transit-time transistor is similar to its vacuum-tube counterpart. Microwave performance to date is very encouraging, and certain advantages over its vacuum-tube equivalent are indicated.

The L3 Coaxial System

The line amplifiers for the L3 coaxial system are designed to compensate for the loss of the four miles of cable which separate the repeaters; the flat amplifiers are used to compensate for equalizer loss and as transmitting amplifiers. The two types are basically similar, consisting of two feedback amplifiers in tandem separated by an inter-amplifier network; in the line amplifier this network is variable and is automatically adjusted to compensate for variations in cable temperature and for small deviations from the nominal four-mile spacing. Coupling networks employing high-precision transformers are used to connect the amplifers to the coaxial cable through the required power separation filters. The low impedance windings of the transformers are center-tapped and a balancing network provided in order to match the cable impedance over the transmitted frequency band. The amplifiers are equipped with plug-in tubes of high figure of merit which were developed for this application. A double-triode output stage is used to obtain improved system signal-to-noise performance. Provision is made for preventive maintenance of vacuum tubes and for a controlled adjustment of gain on an in-service basis. All important components of the amplifier are subject to quality control procedures to assure that the average gain of groups of amplifiers will be held within narrow limits and that individual amplifiers will form a normal distribution around the average. This approach is essential in order to meet system equalization and signal-to-noise objectives. Careful mechanical design and rigid control of the mechanical aspects of manufacture are necessary to minimize gain variations which might be caused by variations of parasitic circuit elements and unwanted feedback effects. Special measures were required to keep the temperature rise within the sealed die-cast housing within tolerable values.

Parasites and Instability in Radio Transmitters

Several types of parasites or spurious oscillations and other forms of radio transmitter instability are described. Methods of locating and eliminating parasitic circuits are discussed..