# 8-W 2-Stage GaN Doherty Power Amplifier Module on 7 \(\times\) 7 QFN for the 5G N78 Band
###### Abstract  
This paper presents a 2-stage GaN Doherty power amplifier module (DPAM) on a compact 7 \(\times\) 7 quad flat no-lead (QFN) package, designed for the needs of 5G massive MIMO base transceiver systems. The interstage and input matching networks employ high-quality factor integrated passive devices (IPDs) to achieve a small form factor. This multi-chip module consists of three GaN-HEMT bare dies used for the driver stage, carrier amplifier, and peaking amplifier. Additionally, two IPD dies are included for the interstage and input matching networks. The external load network is developed using a printed circuit board (PCB). Utilizing a 5G NR signal of 100 MHz bandwidth and a 9.3 dB PAPR within the 3.4-3.8 GHz band, the developed DPAM demonstrated a power gain exceeding 26.8 dB and a power-added efficiency (PAE) greater than 37.8% at a 39 dBm average output power.  
Doherty power amplifier; multi-chip module; integrated passive device; QFN; 5G; MIMO +
Footnote †: journal: Electronics Letters  
0000-0001-5002-569X/00/0000-0001-569X/00000-0001-5 Monolithic microwave integrated circuit (MMIC) technology enables the implementation of DPAs with a high degree of integration, as both transistors and passive components are fabricated through a unified semiconductor process. This integration approach facilitates significant size reduction, making it suitable for compact system designs [8,9]. However, passive devices fabricated using MMIC technology often exhibit relatively low-quality factors compared to surface-mounted components, potentially compromising performance. Moreover, passive elements produced by MMIC processes are generally more expensive than those derived from an IPD process.  
Recently, several DPAMs employing multi-chip modules (MCM) techniques have been reported, where high-power transistor bare dies and high-Q IPDs are compactly integrated within a single package [10, 11, 12]. In [10], an MCM for a DPAM with a 2-stage dual-driver structure was presented with matching networks using GaAs IPD and four GaN-on-SiC bare dies. Since the components using IPD process have relatively low-quality factors compared to the conventional high-Q surface-mounted components, a relatively low PAE of 32.8% was reported at an average output power of 29.9 dBm. In [11], a GaN-HEMT DPAM with an integrated interstage matching network (ISMN) was reported. The load network was implemented on a PCB including a coupler based on a low temperature co-fired ceramic (LTCC). Though this DPAM has a relatively large form factor of 25 \(\times\) 25 mm\({}^{2}\), it exhibited a PAE of 42% at an average output power of 38.0 dBm.  
In this paper, we present an 8-W 2-stage GaN Doherty power amplifier multi-chip module for the 5G N78 band. The proposed DPAM comprises input and interstage matching networks integrated using IPD, along with three GaN-HEMT bare dies for MCM housed in a \(7\times 7\) QFN package. The interstage matching network features a power splitter and phase delay control circuit, as the design employs a single-driver structure rather than a dual-driver configuration to reduce the number of GaN dies and simplify the overall design. To achieve high output power and efficiency by minimizing loss, the load network was implemented on a PCB and surface-mount components with high-quality factor. The measured performances of this module will be discussed and compared with previous DPAMs.