Browse Prior Art Database

High Speed Direct Conversion FM Demodulator

IP.com Disclosure Number: IPCOM000109798D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Arai, Y: AUTHOR [+2]

Abstract

Disclosed herein is a coherent demodulation technique for FM signals with self-contained channel separation capability which can minimize expensive channel separation filters or complex double superheterodyne receiver construction in wide areas of wireless communication. Major areas of application are radio, public paper, mobilephone, and transceiver.

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High Speed Direct Conversion FM Demodulator

       Disclosed herein is a coherent demodulation technique for
FM signals with self-contained channel separation capability which
can minimize expensive channel separation filters or complex double
superheterodyne receiver construction in wide areas of wireless
communication.  Major areas of application are radio, public paper,
mobilephone, and transceiver.

      Fig. 1 shows the basic embodiment of a demodulator with
differentiators. The local reference is a sinusoidal wave whose
frequency equals the center frequency of the received FM signal.  The
local reference is 90-degree phase split and multiplied (mixed) with
the input FM signal to obtain a pair of 90-degree phase split beaten
down signals which form a phase rotating vector.  The rate and
direction of rotation, which can be detected in the successive
differentiator and multiplier, indicates the instantaneous frequency
of the input FM signal with reference to the local reference.  With
the pair of low-pass filters (LPFs) at the mixer outputs, the
sensitivity of the demodulator can be restricted to a predetermined
range of the input signal spectrum.  Thus, channel selection can be
performed by setting the local reference without powerful band-pass
filters or complex double superheterodyne construction.  Figs. 2 and
3 are alternative embodiments with delay lines and RC integrator,
respectively.  These have nearly equivalent functions to that of the
differen...