Logic-based architecture for fsk modulation and demodulation

Abstract

A cost-effective continuous phase logic-based modulator and demodulator are provided to allow communications using binary frequency shift keying (BFSK) as well as M-ary FSK techniques. The modulator of the 1-bit precision modem architecture is based on a 1-bit precision numerically controlled oscillator (NCO), which provides complete programmability with respect to a frequency of the 1-bit precision logic-based modulator and/or demodulator. The output of the 1-bit precision NCO is upconverted to an intermediate frequency using a simple logic function, i.e., XNOR logic. The undesirable portion of the upconverted signal may be suppressed using I/Q image rejection, and/or an appropriate bandpass filter may be used. A band limited, hard limited signal at the high IF is presented to the 1-bit precision demodulator as a receive IF signal, which is treated as a 1-bit quantization of the signal. The receive IF signal is digitally down-converted to a low IF signal to produce an alias signal at the low IF frequency. The received symbols are correlated with expected local frequencies representing a mark and a space. The correlation is integrated in an oversampled manner relative to the symbol interval. A decision is made as to which symbol was received using, e.g., a magnitude comparator.