Direct digital down conversion of a 10.8 MHz intermediate frequency signal in the personal handy phone system

摘要

A system for a direct digital down conversion of a 10.8 MHz intermediate frequency signal in the personal handy phone system. The present invention includes a system that enables a direct digital down conversion of a 10.8 MHz intermediate frequency signal into a digital baseband signal within cell stations and portable stations of the personal handy phone system. To perform this direct digital down conversion of a 10.8 MHz intermediate frequency signal, one embodiment of the present invention uses a hard limiter circuit, a sampler circuit and a digital down converter circuit. The hard limiter circuit of the present invention receives a 10.8 MHz intermediate frequency signal, utilized within cell stations and portable station of the personal handy phone system, and provides a threshold for it. The sampler circuit uses a 19.2 MHz oscillating clock signal to sample the intermediate frequency signal that is output from the hard limiter circuit. Due to spectral leakage, the 10.8 MHz intermediate frequency signal that was input into the sampler circuit is output as an 8.4 MHz intermediate frequency signal. The digital down converter circuit uses an 8.4 MHz signal to perform a digital down conversion of the 8.4 MHz intermediate frequency signal into a digital baseband signal. The present invention provides a system that utilizes only one digital down conversion stage to perform a direct digital down conversion of a 10.8 MHz intermediate frequency signal into a digital baseband signal.