Power Amp Delivers 0.3 W for 28-GHz 5G Bands

This article appeared in Electronic Design and has been published here with permission.

As 5G design-ins increasingly become a reality, there’s also additional momentum for using its higher-frequency bands with their wider bandwidth and performance potential. To make this happen, it’s necessary to have the right RF components, including the transmit-side power amplifier (PA).

To address this opportunity, CML Microcircuits introduced the CMX90A702, a highly linear, medium-power amplifier operating in Frequency Range 2 (FR2) from 26.5 to 29.5 GHz for 5G New Radio (NR) bands n257 and n261 (Fig. 1).

The CMX90A702 is a three-stage GaAs MMIC amplifier delivering +25 dBm (0.3 W) of output power at 1-dB gain compression, with 21 dB of small-signal gain and +32.5-dBm output third-order intercept (OIP3). Target applications include 5G millimeter-wave (mmWave) infrastructure, fixed wireless access (FWA), repeaters and small-cell installations, 5G backhaul links, and customer premises equipment (CPE).

Power added efficiency (PAE) is 28%, while error vector magnitude (EVM) is 4% at 18-dBm mean power. Its RF ports are matched to 50-Ω impedance with an integrated dc blocking capacitor at the output. The PA is easy to monitor and control due to the on-chip temperature-compensated RF-power detector and fast-switching enable circuit.

In addition to the standard table of minimum/typical/maximum specifications and absolute maximum ratings, the 19-page datasheet includes nearly 50 performance graphs across a wide range of parameters and perspectives. Among them is the adjacent channel leakage ratio (ACLR) with a corresponding list of conditions called out on the datasheet (Fig. 2).

There’s also a schematic diagram, bill of materials (BOM), and PCB layout (top and bottom sides) for the EV90A702 evaluation board, along with details of the required PC substrate to use (sorry, no FR4 here) (Fig. 3).

Finally, the datasheet also provides specifics of thermal conditions and related layout (thermal resistance is 31°C/W at TC = 85°C), biasing, and use of its internal control circuit. The CML CMX90A702 PA is offered in a 4- × 4-mm VQFN-20 package; quiescent supply requirement is +4 V/182 mA.