I. Introduction
Phased-array transceivers [1]–[3] are required to overcome path loss and realize advanced multiple-input–multiple-output (MIMO) communication in emerging 5G networks in the 28-/38-GHz bands [4]. Since antenna arrays with high element count are needed, it is important for the transceiver circuits to be compact, scalable and energy-efficient. In particular, wideband low-noise amplifiers (LNAs) that can cover contiguous and/or widely separated narrowband channels of a diverse spectrum [3] with low cost and small die area are of high interest, especially in the 60-GHz [5]–[7] and the 28-GHz bands [3], [8], [9]. Recently, coupled LC resonators have received wide interest in various millimeter-wave (mm-wave) circuits, including LNAs [3], [8]–[10], wide-tuning voltage-controlled oscillators (VCOs) [11], [12], and power amplifiers (PAs) [13], [14]. The resonators can be coupled capacitively, inductively (through an explicit inductor), or magnetically (through a mutual inductance), and each result in a fourth-order transfer function. Magnetic coupling is usually preferred since it results in a lower ripple for a given bandwidth [6]. Recent mm-wave LNAs in this class exclusively use the transimpedance () of weakly coupled transformer-coupled resonators as wideband loads [3], [5], [6].