Designing QPSK Modulator Using LTspice-Based Discrete Components

QPSK (Quadrature Phase Shift Keying) is one of the digital modulation techniques that can encode two bits per symbol based on data that has been divided into two parts, namely even data bits and odd data bits to minimize the bit error rate (BER). In this research, a QPSK modulator is designed using discrete components based on LTspice in order to support developments in digital communication systems for information exchange especially for low frequency applications. LTspice is powerful for examining designs and for predicting the characteristics of electronic circuits. And, discrete components are chosen because the required components are widely available and obtained in the market, so it is easy to implement into a QPSK modulator. QPSK modulator consist of data sources, odd-even data dividers, carrier signals, balanced modulator, odd-even modulated signals and OpAmp circuits. After the entire cicuits of QPSK modulator have been designed by using LTspice, then simulation testing can be carried out in each circuit and the whole, so that it can be known whether the circuit is worked properly. After the testing has been carried out, it was found that the output in each circuit and overall modulator was in accordance with the expected where the QPSK modulator was able to generate a QPSK modulated wave with a frequency of 2 MHz and a data frequency of 500 kHz. This result can be used as a reference to be implemented into a prototype, because based on the simulation results can be implemented to the next development.