# A Wideband Power Amplifier in 65 nm CMOS Covering 25.8 GHz-36.9 GHz by Staggering Tuned MCRs
## 1 Introduction  
The development of 5G communication, satellite communication, and radar has attracted much interest and acquired great demands in high-rate wireless communication. There are mainly two ways to increase the data transmission rate: (1) improve the spectrum efficiency; (2) increase the bandwidth of the spectrum. With the same spectrum efficiency, the data transmission rate increases twice with the doubled bandwidth [1]. In the wideband millimeter-wave band region, an extreme data rate is delivered even under low-order modulation [2]. Also, the higher frequency decreases the antenna size, which is important for phase-array design [1]. The frequency regions n257 (26.5-29.5 GHz), n258 (24.25-27.5 GHz), and n260 (37-40 GHz) are specified as 5G FR2 frequency ranges by the 3 GPP 5G New Radio (NR) Standard [3, 4]. Countries have adopted different frequency bands for 5G or other applications. If a single transmitter possesses the bandwidth to cover multiple or all of the regional frequency bands, it can roam internationally [1, 5, 6], which reduces the system cost and design difficulty. Also, for an FMCW radar, wideband is necessary for improving the range resolution (\(\triangle R\)) [7, 8], which is estimated using  
\[\triangle R=\frac{c}{(2*BW)} \tag{1}\]in which BW is the bandwidth of the radiated chirp [8]. Power amplifiers (PA), one of the most important blocks in millimeter-wave transmitters, have attracted more and more attention, with their output power and bandwidth having important effects on the whole system. The output power of the PA determines the signal distance, and the bandwidth greatly influences the data transmission rate. The challenge of designing a broadband PA is to sustain the wideband small-signal frequency response and broadband power performance simultaneously [9]. There are mainly four ways to achieve wideband millimeter-wave silicon-based power amplifiers: (1) distributed amplifiers; (2) stagger tuning; (3) high-order matching networks; and (4) feedback networks. Distributed amplifiers usually occupy a large area of chip size [10], and achieving a wideband optimal load impedance is difficult in this way [11]. Also, at each stage of the distributed amplifiers, the load impedance is not the optimal value for power matching, leading to a decreased efficiency of the power amplifiers [12; 13]. The stagger-tuning technique makes the multiple amplification stages cascade and resonate at different frequencies to flatten the total gain response [1], which is usually effective to achieve small-signal broadband [14; 15]. In addition, the stagger tuning method sacrifices the gain of the amplifier [16]. High-order matching networks, like Chebyshev filters or high-order LC filters, often consist of several passive components, resulting in a high insertion loss. The feedback technique, i.e., resistance-capacitance feedback network, suffers from deteriorated output power and efficiency [7; 17]. Transformers or transformer-based magnetically coupled resonators (MCR) are high-order LC networks with only one inductor area that are widely used for wideband power amplifiers and low-noise amplifiers [7; 16; 18]. [PERSON] et al. designed a wideband power amplifier with a symmetrical transformer-based MCR providing wideband optimal load impedance [16]. [PERSON] et al. demonstrated a compact wideband high-linear-power amplifier covering 24-42 GHz using a custom-designed distributed balun with wideband optimum load impedance [5]. [PERSON] et al. presented a V-Band wideband power amplifier with the help of a transformer-based radial power combiner and the stagger tuning technique [19]. All these power amplifiers use transformer-based or distributed-balun-based MCRs to realize wideband optimal load impedance by carefully selecting the MCR parameters. [PERSON] et al. indicated that a wideband (46-101 GHz) power amplifier with a high-k interstage transformer can be compensated via a single-peak output-matching network [7].