Direct QAM modulator

Details Direct QAM modulator Direct QAM modulator

1997-04-17

1998-12-22

Mis, David

Modulators

Phase shift keying modulator or quadrature amplitude modulator

332105, 375298, H03C 300, H04L 2736

Patent

active

058523898

ABSTRACT:
A direct QAM modulator for generating a high power QAM modulated signal at microwave frequencies comprises a hybrid to create the required RF signals for I and Q paths. In each path, a rat-race coupler is used to get the in phase and out of phase RF signal. The subsequent circuit blocks in each path consist of a single pole double throw switch (SPDT) switched by the polarity of the incoming data, a reflection attenuator, implemented by using forward biased pin diode terminations and controlled by the absolute values of the baseband pulse amplitude modulation (PAM) signal, and a variable reflection phase shifter to adjust for the phase error. To realize modulated signal filtering and to compensate for the nonlinearities, a combined prefiltering and predistortion block is used to shape the baseband PAM signal in each path. Finally, a power combiner is used to combine signals from the two paths into one high power QAM modulated and filtered output signal at microwave frequency.

REFERENCES:
patent: 5140200 (1992-08-01), Stanton
patent: 5349312 (1994-09-01), Huettner et al.
patent: 5351030 (1994-09-01), Kobayashi et al.
patent: 5453720 (1995-09-01), McCullough et al.
patent: 5477200 (1995-12-01), Ono
patent: 5502421 (1996-03-01), Nakahara
A Broadband I & Q Vector Modulator, G. T. Microwave Inc., Microwave Journal, Dec., 1996, p. 108-112.
A Direct 64QAM Modulator Suitable for MMIC Implementation, Surinder Kumar, Abbas Mohammadi, and David Klymyshyn, unpublished submitted and accepted for publication in Microwave Journal, 16 pages.

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