The paper describes the phase locked loop (PLL) in detail. Emphasis is on Digital Phase Locked loops (DPLL) and All-Digital Phase Locked Loops (ADPLL). Important parameters of the PLLs are described. Different sub-blocks of DPLL and ADPLL are described and discussed in detail. An example design of ADPLL is also discussed. Digital and All Digital PLLs are gaining popularity because of their ease of implementation in FPGA's and ASIC's.

It is shown that the semi-infinite and infinite resistive ladder networks composed of identical resistors can be conveniently analyzed by the use of difference equations or z-transforms. Explicit and simple expressions are obtained for the input resistance, node voltages and the resistance between two arbitrary nodes of the network.

This paper presents a multiplexing scheme that uses a periodic sine like pulse and its orthogonal versions to multiplex analog low pass signals. The sine like pulse is derived by multiplying a few cosine waves whose frequencies are harmonically related. The highest frequency of the cosine wave is decided based on the time instant at which the first zero crossing of the periodic sine like pulse is expected. The lowest frequency of the cosine wave decides the period of the sine like pulse. The number of available phase quadrature versions or orthogonal versions for the periodic sine like pulse is given by 2" where 'n' is the number of cosine waves that are multiplied to generate the periodic sine like pulse. The multiplexed signal is generated by adding the double sideband suppressed carrier (DSBSC) modulated signals generated by multiplying message signals and quadrature versions of the periodic sine like pulse. At the receiver, the message signals are detected using coherent detection. The proposed system requires a bandwidth of 2(1.875W) per signal where W is the highest frequency of the message signals. The bandwidth required per signal in the proposed scheme is more than conventional QCM scheme. However, the proposed scheme allows multiplexing eight signals using three cosine carriers. In QCM, only six message signals can be multiplexed with three cosine carriers and their quadrature versions.

The development of an active sonar system requires knowledge of the properties of the waveforms transmitted by that system. The choice of waveform will determine the ability of the system to resolve targets in range and Doppler, and will also impact the detection capabilities of the system. Modulating the frequency or the amplitude of the transmitted waveform will result in an increased time-bandwidth product. Amplitude modulation, however, results in degradation of power efficiency, so it is more common to use frequency modulated signals. Active sonar performance also depends on reverberation rejection, and thus on pulse design.. This paper is based on matlab simulations, and primarily focuses on the effect of choice of modulating frequency of sinusoidal frequency modulated signals (SFM) on their performance in active sonar systems. The ability of SFM to reject reverberation and avoid mutual interference will also be discussed.