2n-qam macrocell

Abstract

A 2 -QAM macrocell for generating constellations with 2 symbols, where N is the number of bits in the digital data word [D :D ] 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.