Peak-to-Average Power Ratio (PAPR) measures how much the peak power exceeds the average power. PAPR = P_peak / P_avg (linear) or 10 log(P_peak/P_avg) dB. OFDM signals have inherently high PAPR because many subcarriers can add constructively. For N subcarriers with equal power, the theoretical maximum PAPR is N (10 log N dB). With 1200 subcarriers (LTE 20 MHz): theoretical max = 30.8 dB. In practice, the probability of all subcarriers aligning is extremely low. The CCDF (Complementary Cumulative Distribution Function) characterizes the statistical PAPR: at 0.01 percent probability, typical OFDM PAPR is 8 to 12 dB depending on the number of subcarriers and modulation scheme. 5G NR with DFT-s-OFDM (SC-FDMA) uplink: PAPR approximately 6 to 8 dB (lower than OFDM because of the DFT precoding). This lower PAPR was specifically chosen for the uplink to improve handset PA efficiency. PAPR reduction techniques: clipping (simple but causes spectral regrowth), tone reservation (reserve some subcarriers for PAPR reduction), selected mapping (SLM, choose the phase rotation that minimizes PAPR).

How does peak power affect PA design?

The PA must handle the peak power linearly (without compression) to avoid distortion. With 10 dB PAPR, a PA delivering 1 W average must be capable of 10 W peak without significant compression. This means the PA is operating at 10 dB output back-off (OBO) most of the time, where its efficiency is very low. Class AB PA efficiency at 10 dB OBO: approximately 5 to 10 percent (versus 50 to 60 percent at P1dB). This is the PAPR efficiency penalty, and it is the single biggest challenge in modern wireless PA design. Solutions include Doherty PA (maintains efficiency at 6 to 10 dB OBO), envelope tracking (modulates the PA supply voltage to follow the signal envelope), and digital predistortion (DPD, allows the PA to operate closer to compression while correcting the nonlinearity digitally). A Doherty PA with DPD can achieve 40 to 50 percent efficiency at 8 dB OBO, compared to 8 percent for a simple Class AB PA.

How is peak power measured?

Thermal sensors (thermocouples, thermistors): measure average power only. The resistive element absorbs RF power and measures the temperature rise. Insensitive to peak power. Accuracy: plus or minus 0.5 percent. Bandwidth: DC to 110 GHz. Diode sensors: rectify the RF signal. In the square-law region (below approximately minus 20 dBm), the output voltage is proportional to power (no waveform correction needed). Above minus 20 dBm, the diode enters the linear region and waveform correction factors are needed. Modern diode sensors with digital correction handle modulated signals with PAPR up to 12 dB. Peak power sensors use wideband diode detectors with fast sampling (100 MHz+ bandwidth) to capture the envelope of pulsed and modulated signals. Measure pulse power, pulse width, rise time, fall time, overshoot, and droop. Sample rate: 100 Msamples/s to 1 Gsample/s. Applications: radar pulse analysis, OFDM signal characterization, compliance testing. Calorimetric power measurement: most accurate primary standard. Measures total absorbed power from water temperature rise.

Power Metric

Peak Power

/peek pow-er/

Max instantaneous RF power. P_avg = P_peak×duty. PAPR = P_peak/P_avg. OFDM: 8-12 dB PAPR @0.01% CCDF. DFT-s-OFDM (5G UL): 6-8 dB. PA at 10 dB OBO: 5-10% efficiency. Doherty+DPD: 40-50% @8dB OBO. Pulsed radar: P_peak=10-1000 kW, duty=0.1-10%. Measurement: thermal (avg), diode (peak), envelope sensor (100M-1G samples/s).

OFDM: 8-12 dB

Radar: 10-1000 kW

OBO: efficiency hit

Understanding Peak Power

Peak power and average power are fundamentally different quantities with different physical implications. Average power determines thermal design: the heat sink, cooling system, and long-term reliability. Peak power determines linearity requirements: the amplifier compression point, voltage swing limits, and breakdown margins.

The distinction becomes critical in modern wireless systems with high-PAPR signals. An OFDM signal with 10 dB PAPR means the PA must handle 10 times more peak power than average power, forcing it to operate far below its maximum efficiency point. This single issue drives billions of dollars of research into Doherty, envelope tracking, and DPD technologies.

Peak Power Equations

Average power (pulsed):
P_avg = P_peak × τ × PRF
P_peak=100kW, τ=1μs, PRF=1kHz: P_avg=100W

PAPR (OFDM):
PAPR = P_peak/P_avg
Max theoretical: N (# subcarriers)
Practical @0.01% CCDF: 8-12 dB

PA efficiency at OBO:
η_ClassAB ≈ η_max/10^(OBO/10)
10 dB OBO: η drops 10×

PAPR by Signal Type

Signal	PAPR (dB)	PA OBO	Efficiency	PAPR Fix
CW/FM	0	0 dB	50-65%	None needed
QPSK	3.6	4-5 dB	20-30%	Filtering
SC-FDMA	6-8	7-8 dB	15-25%	DFT precoding
OFDM (LTE)	8-11	8-10 dB	8-15%	Doherty+DPD
OFDM (5G 256Q)	10-13	10-12 dB	5-10%	ET+DPD

Common Questions

Frequently Asked Questions

PAPR?

P_peak/P_avg. OFDM: subcarriers add constructively. N subcarriers: max N (30+ dB). Practical @0.01% CCDF: 8-12 dB. 5G UL: DFT-s-OFDM = 6-8 dB (lower). Reduction: clipping (regrowth), tone reservation, SLM (phase rotation). PAPR = biggest PA efficiency challenge.

PA impact?

PA must be linear at peak. 10 dB PAPR: need 10W PA for 1W avg. Class AB @10dB OBO: 5-10% efficiency. Doherty: 20-30% @8dB OBO. Doherty+DPD: 40-50%. Envelope tracking: modulate supply. This PAPR penalty drives multi-billion $ R&D. CW/FM: 0 dB PAPR, no problem.

Measurement?

Thermal sensor: average only, ±0.5%, DC-110GHz. Diode: square-law (below −20dBm), linear (above, needs correction). Peak sensor: wideband diode, 100M-1G samples/s, captures pulse shape. Calorimetric: primary standard (water temperature rise). CCDF measurement: statistical PAPR characterization.

Related Terms

← PCB Antenna Permittivity →

Power Systems

Request a Quote

Need PA efficiency optimization, PAPR reduction, or power measurement? Contact our team.

Get in Touch