Monolithic GaAs-InGaP HBT balanced vector modulators for millimeter-wave wireless systems

Abstract

This paper describes the design and performance of millimeter-wave balanced vector modulators employing the Marconi HBT MMIC technology. Two versions have been fabricated for operation at 38 GHz; the first employs normal Lange couplers whilst the second employs miniaturised microstrip couplem, which reduce the MMIC chip area by more than 40%. With a simple bias Calibration technique the circuits achieve near-perfect constellations w&h negligible amplitude and phase errors Over a wide bandwidth INTRODUCTIONIn recent years there has been a considerable interest in the use of direct carrier modulation in order to reduce the complexity and cost of microwave circuits [l-71. High performance direct vector modulators are required in modem microwave systems like phasedarrays, VSATs, LOS communications and radar applications, with the I-Q vector modulator being widely employed for quadrature modulation schemes [3-51. It consists of a phase splitting power divider that creates two orthogonal channels. Each channel consists of a bi-phase amplitude modulator, which is individually modulated and then combined at the output of the vector modulator. A common technique for realising the single stage bi-phase amplitude modulators in each channel is to a employ reflection topology using a Lange coupler with either coldFETs or cold-HBTs acting as switches on the direct and coupled ports [3-71. The cold-transistors can be controlled with an analogue bias signal to give a continuous range of resistance. Ideally, when the switches are ON the resistance would be zero (thus r=l), whilst when the switches are OFF the

Broad-band HBT BPSK and IQ modulator MMICs and millimeter-wave vector signal characterization

“…We can generate the static constellation diagrams of QPSK or higher order QAM modulations. The 64-QAM extracted constellation diagram can also be seen in [14]. The extraction of the QPSK format at 50 and 110 GHz were also performed, with results similar to those in [14] with slightly different control voltages.…”

“…The 64-QAM extracted constellation diagram can also be seen in [14]. The extraction of the QPSK format at 50 and 110 GHz were also performed, with results similar to those in [14] with slightly different control voltages. For broad-band operation, the lookup table (LUT) method [23] can be used to deal with the different control voltages at IP, IN, QP, and QN ports.…”

“…The vector summation of in-phase and quadrature-phase BPSK modulators can be in many phase and amplitude states by adjusting the control voltages (IP, IN, QP, and QN). The microphotograph of the IQ modulator MMIC was shown in [14] with a chip size of 2 2 mm . For quadrature phase-shift keying (QPSK) modulation, there are four phase states with the same amplitude, which are represented as states of and .…”

“…Therefore, we use the calibration bias method [12] via the static constellation diagram measurement to extract exact amplitude/phase states and minimize the amplitude imbalance and phase imbalance of the IQ modulator. The forward transmission coefficients at 94 GHz are reported in [14]. Based on forward transmission coefficients, EVM calculation is also used to extract the best amplitude and phase states.…”

“…Some BPSK modulators are implemented in the HEMT process [10]- [13], however, they require negative biasing voltage to perform the modulation function. On the contrary, the HBT-based modulators only require positive bias to operate, but they have been reported in literatures [13], [14] with operating frequencies below 50 GHz. Recently, we reported an HBT-based BPSK modulator operating above 50 GHz with a low LO power drive [15].…”