A 24-to 28-GHz 4x1 MIMO Transmitter/Receiver for 5G Phased-Array Applications With High Amplitude and Phase Control

This paper introduces a 4-channel 24- to 28-GHz RF front-end MIMO system designed for 5G applications. The transmitter (Tx) and receiver (Rx) chips are fabricated using 130-nm SiGe BiCMOS technology. The chips contain a 6-bit phase shifter (PS), 1-bit attenuator (ATT), 3-bit variable gain amplifier (VGA), serial peripheral interface (SPI), Wilkinson combiner, power amplifier (PA), and low noise amplifier (LNA). The designed vector-sum PS, employing a current DAC for semi-digitization, achieves a 6-bit phase resolution with minimal root-mean-square (RMS) phase error. This design choice allows for the high bit control of the current DAC within a compact chip area. Four-bit amplitude control is obtained with VGA and ATT. The VGA provides 8-dB amplitude range while ATT enlarges overall amplitude control with additional 8 dB. L-R-L phase compensation technique is utilized to reduce the phase error that arises from ATT. The sub-blocks are designed to operate with low DC power such that the DC power consumption of overall RX and TX is 50 and 97 mW, respectively. The measurement results of a single-channel indicate a gain of 15.5-dB and -25-dBm IP1dB for the RX chip and 26.5-dB and 10-dBm OP1dB for the TX chip while each chip occupies 0.83 mm2. The RX chip exhibits a measured noise figure (NF) of 4.3 dB at 26 GHz. Both Tx and Rx chips achieve 6-bit phase control and 4-bit amplitude control with low RMS phase error of 2.6 degrees and gain error of 0.3 dB. Low RMS gain and phase errors over a wide bandwidth are attributed to the high precision DAC employed in the control of VGA and PS. Both chips are flip-chip packaged and undergo upconversion/downconversion via external mixers on a printed circuit board (PCB). System-level tests with 64-quadrature amplitude modulation (QAM) show an error vector magnitude (EVM) of 2.72% at 27 GHz for RX and 5.02% at 24 GHz for TX, with a 50-MBaud modulated signal applied at a data rate of 300 MBps.