Filter and demodulation arrangement

• US 4,130,806 A
• Filed: 05/23/1977
• Issued: 12/19/1978
• Est. Priority Date: 05/28/1976
• Status: Expired due to Term

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Snijders, Wilfred A. M., Van Doorn, Rudolf A., Van Gerwen, Petrus J., Van Essen, Hendrik A.
• Primary Examiner(s): Richardson, Robert L.
• Assistant Examiner(s): Ng, Jin F.
• Application Number:
  US05/799,884
• Time in Patent Office: 575 Days
• Field of Search: 325/42, 325/44, 325/323, 325/324, 325/487, 178/88, 364/724, 329/50, 329/104, 328/167
• US Class Current: 375/350
• CPC Class Codes: H03D 2200/0047 Offset of DC voltage or frequency
• CPC Class Codes: H03D 2200/0056 including a digital decimation filter
• CPC Class Codes: H03D 2200/006 Signal sampling
• CPC Class Codes: H03D 2200/0082 Quadrature arrangements
• CPC Class Codes: H03D 3/007 by converting the oscillations into two quadrature related signals H03D3/245 takes precedence
• CPC Class Codes: H03D 5/00 Circuits for demodulating amplitude-modulated or angle-modulated oscillations at will H03D9/00, H03D11/00 take precedence
• 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
• CPC Class Codes: H04L 27/06 Demodulator circuits; Receiver circuits

Abstract

A digital filter and demodulation arrangement for passband signals, whose corresponding baseband signal has a bandwidth limited to a given maximum frequency. The passband signals are filtered according to two bandpass characteristics which, apart from their asymmetrical distortion relative to their central frequency, are versions from one another shifted 90° in phase. The filtered passband signals are demodulated with an in-phase carrier and a quadrature carrier and the demodulated signals are combined to a baseband signal.

In the digital filtering process the sampling frequency is reduced from a value higher than twice the highest frequency in the passband signals to a value which is not higher than twice said maximum frequency in the baseband signal and in the digital demodulation and combination processes the reduced sampling frequency is also used so that a considerable reduction in the internal processing speed is obtained.

Claims

1. An arrangement for filtering and demodulating passband signals which are obtained by modulating a carrier in accordance with a baseband signal whose bandwidth is limited to a given maximum frequency, said arrangement comprising means for filtering the passband signals according to a first and a second bandpass characteristic for generating first and second filtered passband signals, which bandpass characteristics apart from the asymmetrical distortion relative to their central frequency are versions of one another shifted 90°

in phase, means for demodulating the first and second filtered passband signals with an inphase carrier and a quadrature carrier respectively for generating first and second demodulated signals, means for combining the first and second demodulated signals, all said means for filtering, demodulating and combining being digital means, the digital filter means including means for sampling frequency reduction for converting signal samples of the passband signals occurring with a first sampling frequency which is higher than twice the highest frequency in the passband signals into signal samples of the first and second filtered passband signals occurring with a second sampling frequency which is not higher than twice said maximum frequency of the baseband signal, and the digital means for demodulating and combining each include means for processing signal samples occurring with the same second sampling frequency.