Direct Conversion Receiver with Digital Signal Processor Demodulator

<div class="htmlview paragraph">In the last few years, attention has been paid to direct conversion receivers for engineering use.</div> <div class="htmlview paragraph">In direct conversion, a vector product of the received signal and the orthogonal oscillator output of the same frequency (orthogonal transformation) is used for direct conversion and demodulation to the baseband.</div> <div class="htmlview paragraph">As compared with current superheterodyne techniques, direct conversion has the following advantages:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">Resonant circuits for radio-frequency stages are not required.</div> </li> <li class="list-item"> <div class="htmlview paragraph">Integration will be possible in the future.</div> </li> </ul> </div> <div class="htmlview paragraph">Because of these reasons, direct conversion will play an important role in the development of compact and adjustment-free tuners.</div> <div class="htmlview paragraph">To demodulate analog modulated signals by direct conversion, highly accurate orthogonal transformation and signal processing sections are required. For this reason, practical application of direct conversion has been difficult.</div> <div class="htmlview paragraph">Our objective is to develop a direct conversion receiver for automotive use which enables AM and FM broadcast reception. We fabricated a prototype receiver with the following features:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">To ensure accurate signal processing for demodulation, we used digital signal processors (DSP).</div> </li> <li class="list-item"> <div class="htmlview paragraph">Signal compensation is performed at the baseband.</div> </li> </ul> </div> <div class="htmlview paragraph">In this paper, we would like to report on the demodulation method, signal compensation at the baseband, and briefly outline a prototype receiver with such sophisticated technologies.</div>