FM Demodulator

• US 4,488,119 A
• Filed: 02/04/1982
• Issued: 12/11/1984
• Est. Priority Date: 02/20/1981
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Marshall, Christopher B.
• Primary Examiner(s): Grimm, Siegfried H.
• Assistant Examiner(s): MIS, DAVID C
• Application Number:
  US06/345,863
• Time in Patent Office: 1,041 Days
• Field of Search: 455/214, 455/337, 329/50, 329/122, 329/124, 328/25
• US Class Current: 329/323
• CPC Class Codes: H03D 3/007 by converting the oscillations into two quadrature related signals H03D3/245 takes precedence
• CPC Class Codes: H03D 3/22 by means of active elements with more than two electrodes to which two signals are applied derived from the signal to be demodulated and having a phase difference related to the frequency deviation, e.g. phase detector
• CPC Class Codes: H03D 7/165 at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature combined with amplitude demodulation H03D1/2245, combined with angle demodulation H03D3/007; N-path filters H03H19/002

Abstract

An FM demodulator in which an incoming FM signal (2a sin(ω+δω)t) is demodulated to baseband (δω) by applying it to first and second mixers (12, 14). The output (b sin ω t) of a local oscillator (16) is applied to one (14) of the mixers and is also applied to the other (12) of the mixers via a 90° phase shifter (18). The phase of the output of one of the mixers is shifted so as to be in phase or in antiphase to the other and is applied together with the output of the other of the mixers to a signal divider (22), the output of which comprises the baseband signal which is substantially independent of fading.

Claims

1. A FM demodulator which comprises:

an input terminal for receiving a frequency-modulated input signal;

first and second mixers each having first and second inputs and each having an output, the first inputs of the mixers being connected to the input terminal;

first means for producing a first local oscillator signal;

second means for producing a second local oscillator signal having the same frequency as, and being phase shifted by 90°

relative to, the first local oscillator signal, the second input of the second mixer being connected to the first means, the second input of the first mixer being connected to the second means;

a signal divider including a first input, a second input and an output which comprises an output of the demodulator, the first input of the divider being coupled to the output of the first mixer, and

an integrator coupled to the second input of the divider and to the output of the second mixer, so that a low frequency signal at the output of the second mixer is phase shifted in the integrator by 90°

more than the phase of a low frequency signal at the output of the first mixer, the low frequency signals being applied to the divider, whereby a signal corresponding to a modulating signal of the input signal is obtained at the output of the divider.