All-digital pseudo-coherent (PC) FSK modems

A detailed study of the PC (pseudocoherent) and DID (double-integrate-and-dump) FSK (frequency shift keying) demodulators by computer simulation is presented. In addition, the hardware realization of the demodulators is described. It is shown that both demodulators perform nearly as well as the coherent schemes. They are also both basically suitable for realizing a VLSI for FSK modems. Typical silicon areas required for a complete modem with these demodulators are worked out and are on the order of 19 mm² (based on 4-μm technology). This is up to an order of magnitude less than that of the current IC chips like the AMD 7911. Since both of these demodulators have a 1-2-dB SNR (signal-to-noise ratio) advantage over the noncoherent scheme, it is perhaps possible to further reduce the receiver input BPF requirements while using these demodulators. Hence, the PCFSK demodulation technique is suggested as a reliable and cost-effective technique to be implemented in modem ICs