# December 1993, Volume 2, Number 4

**D. Pal, S. K. Sanyal, R. Nandi**
[full-text]

Generation of Digital Modulation for Optical Communication Using Tunable Active-R Oscillator

This paper describes the design of an active-R biphase oscillator using a pair of matched Operational Amplifier (OA) and a few resistors. The frequency of oscillation of such oscillator is tunable by a resistor (R_{0}). The oscillator can be readily extended to the digitally tunable version by replacing the tuner resistor with a Binary Weighted Switched Resistor Array (BWSRA). The digitally tunable oscillator can also be hooked up with microprocessor using CMOS CD 4066 switches. Generation of BFSK/BPSK wave modulations have then been considered using this oscillator. Subsequently, the BFSK/BPSK. modulations are used to excite 4N25 Optoisolator. The received BFSK/BPSK signals from the Optoisolator are in full conformity with the corresponding transmitted ones. Experimental results are included.

**J. Valsa**
[full-text]

LTP - A Tutorial Program for Analysis of Linear Two - Ports

The paper describes basic possibilities offered by the program LTP (Linear Two-Ports) in teaching electrial networks theory. At the same time the most important algorithms used in the program are briefly described. The program LTP analyses immittance and transfer functions of two-ports in the domain of complex variable p, in the frequency domain and in the time domain. The results can be obtained in symbolic, semisymbolic and numerical form (with optional graphical representation of the numerical results). The program is user friendly and can be used easily by anyone.

**A. I. Rybin, J. K. Trochimenko, M. V. Radionova**
[full-text]

Analysis of Irregular Networks Using Diakoptic Modification of Admittance Matrix Inversion

A special method of admittance matrix inversion is presented in this article. This method is based on diakoptic tearing of non-standard networks and then solving the subnetworks step by step with added torn branches. It is suggested for computer-aided analysis of large networks.

**S. Novak**
[full-text]

Design of Amplifiers with Potentially Unstable Transistors

Paper presents overview of methods used for stabilization of high frequency and microwave transistors amplifiers using potentially unstable transistors. The S-parameter approach is used for analysis of the amplifier stability over the required bandwidth. The treatment takes in consideration the influence of the operating conditions on noise, gain and mismatch for the particular application. Because the subject is treated in the literature only briefly, the summary presented in this short paper shows to the designer methods used in practical design.

**Z. Smekal**
[full-text]

The Discrete System and Its Models for Digital Signal Processors

The discrete system is mostly described with the help of the system transfer function and the zero input response is usually neglected. In this paper the state-space equations express the total response of the discrete system, and they are arranged to a digital signal processor implementation.