초록 ▼

A direct conversion FM receiver that includes AC coupling and automatic gain control employs an offset frequency at the first local oscillator. The offset frequency prevents the frequency spectrum occupied by the signal modulation from being affected by AC coupling. The offset frequency is chosen so

A direct conversion FM receiver that includes AC coupling and automatic gain control employs an offset frequency at the first local oscillator. The offset frequency prevents the frequency spectrum occupied by the signal modulation from being affected by AC coupling. The offset frequency is chosen so that it translates the frequency spectrum of the received signal outside the DC notch created in the spectrum by the AC coupling. To conserve battery supplied power, an error amplifier coupled between the output of the receiver and the first local oscillator maintains the offset frequency after it has been established by a frequency synthesizer, which is then turned off.

대표청구항 ▼

A direct conversion receiver for processing frequency modulated radio signals that are centered about a carrier frequency, the frequency modulation extending a first sideband bandwidth above and below the carrier frequency, the receiver comprising: means for receiving the radio signals, said receivi

A direct conversion receiver for processing frequency modulated radio signals that are centered about a carrier frequency, the frequency modulation extending a first sideband bandwidth above and below the carrier frequency, the receiver comprising: means for receiving the radio signals, said receiving means having an output; a pair of signal paths each having an input coupled to the output of the receiving means; a local oscillator tuned to a local oscillator frequency and having an output; each of said signal paths including a first mixer serially coupled therein, each of said first mixers having a local oscillator input coupled to the local oscillator output; each of said signal paths further including an AC coupling means serially coupled therein, each of said AC coupling means producing a notch centered at DC in a frequency response of each of said signal paths, said notch extending a second sideband bandwidth above and below DC; wherein the local oscillator frequency is set equal to the carrier frequency plus an offset frequency, said offset frequency being greater than or equal to the sum of the first and second sideband bandwidths.