Northrop Grumman Systems Corporation

Trw Limited

Ryan M Desrosiers

Craig A Hornbuckle

Harvey L Berger

Methods and devices for predistorted 12/4 Quadrature Amplitude Modulation that compensate for distortion from a nonlinear element. Modulator input bits are mapped ( ) to a plurality of nonreturn-to-zero (NRZ) modulator control bit ( ). The mapping is determined by desired points on a 12/4 QAM constellation. At least one phase shift device ( ) receives an input signal and at least one of the plurality of modulator control bit. At least two quaternary phase shift keying (QPSK) devices ( ) receive phase shifted signals from at least one phase shift device. Each of at least two QPSK devices receives at least one of the plurality of NRZ symbols. An attenuator ( ) that attenuates a first QPSK signal outputted from a first QPSK device of the at least two QPSK devices. A summer ( ) sums the attenuated first QPSK signal with a second QPSK signal. The second QPSK signal is outputted from a second QPSK device of the two QPSK devices. The summer outputs a predistorted 12/4-QAM signal. The plurality of modulator control bit control the at least one phase shift devices and the two QPSK modulators to achieve the desired points on the 12/4 QAM constellation.

Efficient pre-distorted 12/4 QAM modulator

A 2 -QAM macrocell for generating constellations with 2 symbols, where N is the number of bits in the digital data word &lsqb;D :D &rsqb; applied to the macrocell. Since the digital data word is applied directly to the macrocell, the need for a digital mapping chip is thus eliminated thus reducing the complexity and power consumption of the circuit. An important aspect of the invention is that the 2 -QAM macrocell is amenable to being fabricated as a single microwave monolithic integrated circuit (MMIC) or integrated circuit (IC). As such, a QAM circuit can be formed from two MMICs; the 2 -QAM macrocell and a quadrature hybrid phase shifting device formed on separate MMIC to form a 2 -QAM circuit or one MMIC containing both the 0/90 degree phase shifter and the 2 -QAM circuit. The phase shifting device is used to provide the in-phase and quadrature phase components of the local oscillator signal. Since the QAM circuit in accordance with the present invention only requires one or two MMIC chips; the complexity and cost of the circuit is reduced and the need for tuning is obviated. The 2 -QAM macrocell may be formed from Gilbert transconductance multipliers with GaAs heterojunction bipolar transistor (HBT) technology, thus providing maximum symbol rates in excess of 1 Gsps.

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Tigard, OR, United States of America

Ryan M Desrosiers