Demodulators – Phase shift keying or quadrature amplitude demodulator
Patent
1994-08-17
1995-07-25
Mis, David
Demodulators
Phase shift keying or quadrature amplitude demodulator
329310, 375324, 375333, H03D 300, H03D 304, H04H 100
Patent
active
054365910
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention is related to a demodulator for radio data signals according to the introductory part of claim 1.
By means of the well known radio data system data signals can be transmitted additionally to the audio signals, which data signals e.g. comprise the name of the transmitted program and other information. In order to assure the compatibility with the audio signals as well as with traffic broadcast signals for FM stereo radio transmission the carrier of 57 kHz used also for traffic broadcast transmission is modulated with the data to be transmitted, wherein, however, the sidebands are choosen different from the modulation frequencies used for the different signals of traffic broadcast transmission. A biphase coding is used effecting that no spectral components result at 57 kHz and that the clock is transmitted implicitly. The whole spectrum of the modulated radio data signals, in the following called RDS signals, is limited to .+-.2,4 kHz.
Conventional RDS decoders rely on the use of phase locked loops. In the magazine Funkschau No. 7/1988, page 42, a RDS decoder is disclosed to which the 57 kHz signal is fed after amplification and amplitude limitation, i.e. as a square wave signal. RDS information is demodulated by means of a synchronous demodulator with carrier recovery (Costas loop).
It is the object of the present invention to provide a demodulator for RDS signals in which no delay due to rise times of phase locked loops occur.
According to the present invention this problem is solved by a demodulator comprising the features described generally in FIG. 1.
The demodulator according to the present invention can advantageously be built up by means of digital components only, allowing a low cost realization as an integrated circuit and rendering expensive matching works during production unnecessary.
The demodulator according to the present invention can also be put into effect by means of suited programs for signal processors or other micro electronic components. Since the demodulator according to the present invention can work on a high speed it may advantageously be used in a broadcast receiver in which short periods checks on alternative frequencies are performed (e.g. according to DE 41 03 062 A1) without disturbing the reception of the actual tuned frequency.
For producing the second square wave signal in an embodiment of the invention a signal on about a subcarrier frequency is produced the phase of which is matched to the phase of the received RDS signal from time to time. In a further embodiment the second signal is produced by delaying the first signal by half a RDS data period.
Advantageous embodiments of the invention are recited in the subclaims and will be explained by means of examples of the invention and their properties and advantages with reference to the drawing, in which:
FIG. 1 shows a block diagram of a demodulator according to a first embodiment
FIG. 2 is a block diagram of a first pulse former being part of the demodulator according to FIG. 1
FIG. 3 is a block diagram of a gate circuit being part of the demodulator according to FIG. 1
FIGS. 4 and 5 show evaluation circuits being part of the demodulator according to FIG. 1
FIG. 6 shows a further evaluation circuit being part of the demodulator according to FIG. 1
FIG. 7 shows an embodiment of a logic circuit being part of the demodulator according to FIG. 1
FIG. 8 is a block diagram of a demodulator according to a further embodiment of the invention
FIG. 9 is a block diagram of a pulse former being part of the demodulator according to FIG. 8
FIG. 10 is a schematic diagram of RDS signal vectors of various signals occurring in the demodulator according to FIG. 8
FIG. 11 is a block diagram of a circuit for recovering data clocks being part of the demodulator according to FIG. 8
FIG. 12 shows time diagrams of signals in the circuit arrangement according to FIG. 11
FIG. 13 is a block diagram of a demodulator according to a third embodiment of the invention
FIG. 14 shows time diagram of signals occurring in t
REFERENCES:
patent: 4092491 (1978-05-01), Frazer
patent: 5001728 (1991-03-01), Fuldner
patent: 5150070 (1992-09-01), Rinaldi et al.
patent: 5175507 (1992-12-01), Roither
patent: 5222254 (1993-06-01), Verron et al.
patent: 5278560 (1994-01-01), Hegeler et al.
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