A cardiac pacemaker model is described based on a close approximation of the properties of cardiac pacemaker cells. It is a minimum-parameter model which has a simple relaxation oscillator circuit as its main element. The pacemaker model is analyzed in detail in order to show that its behaviour is similar to that of cardiac pacemaker cells. The main feature of the model is the possibility of controlling the time course of phase 4 depolarization, the threshold level and the maximum level of repolarization. Emphasis is placed on phenomena of acceleration and deceleration of the pacemaker model by pulsatile stimulation, and on synchronization and frequency entrainment. Finally it is noted that this particular pacemaker model is very useful for the study of interactions between cardiac pacemakers and the description of the mechanism of arrhythmias.

A cardiac pacemaker model

The basic junction-transistor multivibrator circuit is analyzed from the point of view of a circuit designer who Wishes to know: (a) how to predict the performance of a particular configuration, and (b) how to synthesize a multivibrator circuit, which may be either astable, bistable, or monostable, from a given set of specifications. The analytical method consists of breaking the multivibrator circuit (two basic, well-known configurations are treated) at a suitable point and using, the two terminals thus obtained as a driving-point pair to derive a useful V-I characteristic. In part I of the paper, the static driving-point resistance characteristics arc derived theoretically and compared to experimental measurements. In part II, transient and high-frequency effects are considered and the two-terminal analysis is extended to derive a prediction of the maximum frequency, or pulse repetition rate, at which the regenerative mode of operation can take place. Part III of the paper treats the problem of circuit synthesis. Using the results of parts I and II, straightforward methods are developed which permit the circuit designer to uniquely determine the seven circuit parameters which must be specified in the design of symmetrical multivibrators. Several design examples of astable, monostable, and bistable configurations are given.

Two-Terminal Analysis and Synthesis of Junction Transistor Multivibrators

Frequency and transient response equations for the current-transfer ratios of the double-base diode are calculated from theory and checked experimentally. To obtain these results, the device is operated as a small signal amplifier in the negative-resistance region and the frequency response characteristics thus obtained are used to predict the device behavior. The effects of carrier recombination and electric field upon the response characteristics are evaluated and experimental results are presented.

Small-signal wave effects in the double-base diode

Carrier transport in unijunction transistors is due primarily to electric fields rather than diffusion gradients. Thus, the high-frequency and transient response characteristics of unijunction transistors are considerably different from the characteristics associated with diffusion type devices. The high-frequency and transient response characteristics of silicon unijunction transistors are described. A previously published solution of the electrodynamic equations, taking into account field and recombination effects, is used to calculate theoretical frequency and transient response characteristics which are subsequently compared to experimental measurements. It is shown that: 1) Electric field effects lead to resonance characteristics which are somewhat similar to those encountered in wave interference phenomena. 2) The frequency response characteristics of unijunction transistors are predominantly determined by the electric field gradient for high fields and by recombination effects for low fields. 3) The large-signal transient response of unijunction transistors is characterized by at least two time constants, one of which is related to transit time and the other to minority carrier lifetime. 4) The maximum large-signal switching speeds and minimum trigger energy of regenerative unijunction transistor circuits depend upon both the electric field and lifetime characteristics of the device.

Transient Response Characteristics of Unijunction Transistors

The static characteristics of unijunction transistors are exhibited by two surfaces in three-dimensional space. This representation is employed to examine a general formulation of the problem of analysis and design with a device that is characterized by a nonlinear relationship among four variables.

Generalized Characterization of Unijunction Transistor Networks

The operation and design of a novel semiconductor multivibrator circuit is described Consisting of one double-base diode, one diode, three resistors, and one capacitor, the diode multivibrator affords a circuit economy of two-to-one over the more conventional Eccles-Jordan configuration The active element is the double-base diode, which is a three-terminal single-junction negative-resistance semiconductor device Applications of the diode multivibrator to square-wave oscillators and delayed-pulse generators are illustrated Control of the period of oscillation or variation of the pulse-delay time is accomplished by the variation of a single capacitor Hence, this new circuit simplifies the design of astable, monostable or bistable multivibrators

E. Keonjian

Papers

A Semiconductor Diode Multivibrator