Elimination of bandpass filter after quadrature modulator in mod

Details Elimination of bandpass filter after quadrature modulator in mod Elimination of bandpass filter after quadrature modulator in mod

1998-04-21

2000-02-22

Mis, David

Modulators

Phase shift keying modulator or quadrature amplitude modulator

375308, H03C 300, H04L 2720

Patent

active

060284935

ABSTRACT:
A modulation synthesizer circuit produces a fixed intermediate frequency unmodulated signal without harmonics aliasing back into the transmit spectrum, thus, eliminating the need for a bandpass filter. The modulation synthesizer circuit includes a phase shifter placed before the down conversion mixer. The phase shifter may be placed outside the modulation synthesizer loop such that the phase shifter produces quadrature carrier wave signals to the down conversion mixer. In the alternative the phase shifter may be kept within the modulation synthesizer loop and produce quadrature modulated transmit signals to the down conversion mixer. Any harmonic frequencies generated by the phase shifter are harmonics of the carrier wave signal or modulated transmit signal. Thus, with the appropriate choice of carrier wave signal or modulated transmit signal, any harmonics generated by the phase shifter can be prevented from aliasing back into the transmit spectrum and therefore need not be filtered. Consequently, the bandpass filter typically found after the quadrature modulator can be eliminated.

REFERENCES:
patent: 4360788 (1982-11-01), Erps et al.
patent: 4870384 (1989-09-01), Thomas
patent: 5412951 (1995-05-01), Nystrom et al.
patent: 5424687 (1995-06-01), Fukuda

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