Wireless Standards and Protocols Cellular and 5G Informational

What are the power class definitions for 5G NR user equipment and how do they affect PA design?

What are the power class definitions for 5G NR user equipment and how do they affect PA design? 3GPP TS 38.101 defines multiple power classes for 5G NR UE (User Equipment), each specifying the maximum transmit power and the required PA performance: (1) FR1 power classes: Power Class 3 (default): maximum output power = 23 dBm (200 mW). This is the standard for smartphones. The PA must deliver 23 dBm at the antenna port (after all RFFE losses: typically 3-4 dB for filters, switches, and matching). PA output at the PA port: 26-27 dBm. Power Class 2: maximum output power = 26 dBm (400 mW). Used for fixed wireless access (FWA) devices and some high-power smartphones. Requires a more powerful PA (29-30 dBm at the PA port). Increases the uplink coverage by approximately 3 dB. Power Class 1: maximum output power = 31 dBm (1.26 W). Used for vehicle-mounted UE and FWA CPE. Requires a high-power PA (GaN or GaAs, 34-35 dBm at the PA port). (2) FR2 power classes: Power Class 1: maximum EIRP = 43 dBm. Used for CPE (Customer Premises Equipment) with large antenna arrays. Power Class 2: maximum EIRP = 33 dBm. High-end smartphones with 4-module AiP configuration. Power Class 3: maximum EIRP = 23 dBm. Standard smartphones (default for FR2). Power Class 4: maximum EIRP = 34 dBm. Enhanced mobile broadband devices. (3) PA design implications: for FR1 Power Class 3 (23 dBm): PA technology: GaAs HBT (mainstream) or CMOS (emerging for cost reduction). PAE requirement: > 35% at 23 dBm (to manage heat and battery life). Linearity: meet EVM ≤ 3.5% for 256QAM at rated power. This requires DPD or ET (envelope tracking). The PA typically achieves 30-33 dBm P1dB, operating at 7-10 dB back-off for 256QAM. For FR1 Power Class 2 (26 dBm): PA must deliver 3 dB more power. This doubles the DC current and heat dissipation. The PA die area increases by approximately 50%. Higher power also tightens the adjacent channel leakage (ACLR) budget.

Category: Wireless Standards and Protocols

Updated: April 2026

Product Tie-In: Filters, PAs, Switches, Front End Modules

5G NR UE Power Classes

The power class selection has cascading effects on the entire RFFE design: PA technology, thermal management, battery life, and regulatory compliance.

Envelope Tracking for Power Class 3

(1) Envelope tracking (ET) modulates the PA supply voltage to follow the signal envelope: at low envelope amplitudes: the supply voltage is reduced, keeping the PA in its efficient compressed region. At peak amplitudes: the supply voltage is increased to allow full output swing. Benefit: PAE improvement of 5-15% compared to fixed-bias operation, translating to 30-40% DC power reduction and significant thermal reduction. ET is now standard in all flagship 5G smartphones (Qualcomm QET7100, MediaTek MT6382). (2) ET bandwidth: the ET modulator must track the signal envelope with sufficient bandwidth. For a 100 MHz 5G NR carrier: the envelope bandwidth is approximately 200-300 MHz (2-3× the signal bandwidth). The ET modulator must achieve > 40% efficiency at 200-300 MHz bandwidth. This is a significant analog design challenge.

5G NR Power Classes

FR1 PC3: P_max = 23 dBm (200 mW) — smartphones
FR1 PC2: P_max = 26 dBm (400 mW) — FWA
FR1 PC1: P_max = 31 dBm (1.26 W) — vehicles
FR2 PC3: EIRP_max = 23 dBm — smartphones
FR2 PC1: EIRP_max = 43 dBm — CPE

Common Questions

Frequently Asked Questions

Why is FR2 specified in EIRP instead of conducted power?

At mmWave frequencies, the antenna is typically integrated with the PA in an AiP module. There is no connectorized RF port where conducted power can be measured. Therefore, 3GPP specifies the performance in terms of EIRP (Effective Isotropic Radiated Power) and EIS (Equivalent Isotropic Sensitivity), which are measured over the air (OTA). The EIRP includes both the PA output power and the antenna gain: EIRP = P_conducted + G_antenna (dBi).

What is the battery impact of higher power classes?

Power Class 2 (26 dBm) vs Power Class 3 (23 dBm): the PA DC power approximately doubles (3 dB more output). For a typical 5G call: the TX PA consumes 1-3W (Class 3) vs 2-6W (Class 2). Battery impact: Class 2 reduces the continuous TX talk time by 20-30%. This is why Class 2 is primarily used for stationary devices (FWA, CPE) with external power, not for battery-powered smartphones.

How does power control affect the PA design?

5G NR uses dynamic power control: the base station commands the UE to adjust its TX power based on the path loss and interference conditions. The power control range: -40 dBm to +23 dBm (63 dB range for Class 3). The PA must maintain acceptable linearity (EVM) across this entire range. At low power (< 0 dBm): the PA operates deep in the linear region (no linearity issue). At high power (near 23 dBm): EVM and ACLR are the critical constraints. The PA bias must be adjusted with power level (gain steps, bias current scaling) to optimize efficiency and linearity at each power level.

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