Radio receiver

• US 4,618,967 A
• Filed: 06/26/1984
• Issued: 10/21/1986
• Est. Priority Date: 07/14/1983
• Status: Expired due to Fees

• Current Assignee: STC PLC (f/k/a Standard Telephones and Cables)
• Original Assignee: STC PLC (f/k/a Standard Telephones and Cables)
• Inventors: Vance, Ian A. W., Neale, Michael W.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/624,749
• Time in Patent Office: 847 Days
• Field of Search: 375/80, 375/38, 375/39, 375/102, 375/75, 375/45, 375/88, 375/82, 375/86, 455/205, 455/214, 329/126, 329/110, 329/122, 329/124, 329/50
• US Class Current: 375/324
• CPC Class Codes: A23V 2002/00 Food compositions, function of food ingredients or processes for food or foodstuffs
• CPC Class Codes: A23V 2250/044 Malic acid
• CPC Class Codes: A23V 2250/161 Magnesium
• CPC Class Codes: A23V 2250/18 Lipids
• CPC Class Codes: A23V 2250/1842 Lecithin
• CPC Class Codes: A23V 2250/1886 Stearic acid
• CPC Class Codes: A23V 2250/26 Saccharin
• CPC Class Codes: A23V 2250/5114 Dextrins, maltodextrins
• CPC Class Codes: A23V 2250/61 Glucose, Dextrose
• CPC Class Codes: A23V 2250/628 Saccharose, sucrose
• CPC Class Codes: A23V 2250/6406 Glycerol
• CPC Class Codes: A23V 2250/6418 Mannitol
• CPC Class Codes: A23V 2250/642 Sorbitol
• CPC Class Codes: A23V 2250/708 Vitamin C
• CPC Class Codes: H03D 1/22 Homodyne or synchrodyne circuits receiver circuits H04B1/30
• CPC Class Codes: H03D 3/007 by converting the oscillations into two quadrature related signals H03D3/245 takes precedence
• CPC Class Codes: H04L 27/1525 using quadrature demodulation

Abstract

A radio receiver for frequency modulated signals in which direct conversion techniques are used to provide zero I.F. quadrature baseband signals I & Q. The I & Q signals are limited (11,12) to form square wave signals and pulse forming networks (13,14) derive pulse sequences the frequencies of which represent the polarity changes in the square wave signals. Each square wave is multiplied (15,16) by the pulse sequence derived from the other square wave to produce a unipolar pulse train. The two unipolar pulse trains are combined (17) to give a digital output signal the frequency of which is equal to the sum of the frequencies of the two pulse trains. Low pass filtering the output signal produces a simulation of the original baseband modulation.

Claims

1. A radio receiver for receiving frequency modulated signals on an R.F. carrier signal, wherein the received signals are mixed with a local oscillator signal at the carrier signal frequency to produce quadrature baseband signals in two separate signal channels, the receiver including a demodulator arrangement for the baseband signals, the demodulator arrangement including means for limiting the baseband signals in each signal channel to form square wave signals in quadrature, means in each channel to derive from the square wave signals in that channel a sequence of pulses the frequency of which is representative of the polarity changes in the square wave signal, means for multiplying the pulse sequence in each channel by the square wave signal in the other channel to produce two unipolar pulse trains, the pulse frequency in each unipolar pulse train being equal to that of the pulse sequence from which it is derived, and means for generating an output pulse signal the frequency of which is equal to the sum of the frequencies of the two unipolar pulse trains such that when the output pulse signal is low pass filtered it simulates information modulated on the R.F. signal.

2. A receiver according to claim 1 in which the pulse deriving means in each channel comprises a differential amplifier to one input of which is fed the square wave signal, and an integrating RC network via which the square wave signal is fed to the other input of the differential amplifier.

3. A receiver according to claim 2 in which the two unipolar pulse trains are produced with opposite polarities, the output pulse generating means comprising means for algebraically subtracting one unipolar pulse train from the other unipolar pulse train.

4. A receiver according to claim 3 in which the means for multiplying the pulse sequence in each channel by the square wave signal in the other channel comprises a double balanced muitiplier circuit, each multiplier circuit has an output current mirror load, the polarities of the output currents being opposite, the current mirror outputs of the two multipliers being combined and applied to a capacitor or low pass filter to form the simulated information modulation on the R.F. signal.

5. A method of demodulating frequency modulated signals on an R.F. carrier signal including the steps of mixing the modulated signals with a local oscillator signal at the carrier signal frequency to produce separate quadrature baseband signals, limiting the quadrature baseband signals to produce separate square wave signals in quadrature, deriving from each square wave signal a sequence of pulses the frequency of which is representative of the polarity changes in the square wave signal, multiplying each square wave signal by the pulse sequence derived from the other square wave signal to produce two unipolar pulse trains the pulse frequency of each being equal to that of the pulse sequence from which it is derived, and combining the two unipolar pulse trains to produce an output signal the frequency of which is equal to the sum of the frequencies of the two unipolar pulse trains.

6. An integrated semiconductor electronic circuit including a demodulator for a direct conversion radio receiver for frequency modulated signals, the demodulator comprising means for limiting the baseband signals in each signal channel to form square wave signals in quadrature, means in each channel to derive from the square wave signals in that channel a sequence of pulses the frequency of which is representative of the polarity changes in the square wave signal, means for multiplying the pulse sequence in each channel by the square wave signal in the other channel to produce two unipolar pulse trains, the pulse frequency in each unipolar pulse train being equal to that of the pulse sequence from which it is derived, and means for generating an output pulse signal the frequency of which is equal to the sum of the frequencies of the two unipolar pulse trains.