DESIGN AND IMPLEMENTATION OF HIGHER ORDER DIFFERENTIATOR USING MICROSTRIP LINES

Abstract

The differentiator is a device that performs the mathematical operation of differentiation providing as an output signal the derivative of an arbitrary input signal in the time domain. The differentiation operation can be used directly in signal peak detection and in positive-going or negative-going slope recognition. Besides, differentiators have been used extensively in several areas such as signal processing or pulse generation. Particularly, they constitute an important element in the analysis of signals in radar and sonar systems, in the processing of biomedical or biomechanical data, and in the calculation of geometrical parameters in image processing. Moreover, they play a significant role in reconfigurable pulse shapers and in photonic-based microwave waveform generators. Digital differentiators are, in general, limited by the operational frequency and bandwidth, which results from the maximum achievable sampling frequency. A wider bandwidth solution can be achieved by using optical devices. So far, the differentiator are mainly implemented in circuits for low-speed applications. Thus the implementation of these circuits for high frequency applications has been largely ignored. In this project, simple and accurate formulations are employed to represent stable and optimized discrete-time infinite impulse response processes for first and higher order differentiator in the Zdomain. These formulations, in conjunction with the representations of transmission-line elements in the Z-domain, leads to transmission-line configuration that are eligible for wide-band microwave circuits. In particular, many Z domain formats of transfer functions have been obtained to represent the characteristics of a differentiator. Design simulations for digital differentiator are performed in Agilent SystemVue. In order to translate these circuits for high frequency application, T-parameter (chain scattering parameter) is employed. ADS simulations were used to accurate determine the final design. The designed models are implemented using non-uniform microstrip lines in Agilent ADS and Agilent EMPro. Simulation results shows proposed models as good candidate for wide band microwave application. Finally the fabrication of microwave differentiators are done using non-uniform microstrip lines on a RT/duroid® 5880 substrate.