EVM to SNR Calculator

This tool converts from Error Vector Magnitude (EVM) to Signal-to-Noise Ratio (SNR).

In order to calculate SNR the following are required:

  • EVM% (use this tool to convert from dB to %)
  • Peak-to-Average Power Ratio (PAPR). Use the table below to find the PAPR of a modulated signal. 

	

			

		

						

				

				

                

			

			
						

		

		






Formula





SNR = – [PAPR + 20 * Log10 (EVM% / 100)]





Example EVM to SNR calculation





If you want to calculate the SNR for a QPSK waveform for instance, use the PAPR value of 1.76 dB from the table below in the calculator above. 





For a 1% EVM, the SNR is 38.24 dB. As the EVM increases the SNR degrades and at a certain point it will become difficult to demodulate the signal. 





Background





Error Vector Magnitude (EVM) is a metric used to quantify the distortion and impairment in a transmitted signal. 





It is mainly used in communication systems and more specifically in the area of modulation and demodulation. 





EVM measures the difference between the ideal or desired transmitted signal and the actual received signal. This difference is calculated in terms of both amplitude and phase. 





EVM is usually expressed in percentage and a lower EVM value indicates a higher quality and accuracy of the transmitted signal. 





There are several factors that can contribute to EVM, such as 





    

  • Amplifier non-linearity, 
    • 




  • Phase noise
    • 




  • Amplitude distortion
    • 




  • Receiver noise figure
    • 






By measuring and analyzing the EVM of a transmitted signal, RF systems engineers can evaluate the performance of the system and identify any potential problems or areas of improvement. Overall, EVM is a crucial parameter in evaluating the performance and quality of modulation and demodulation systems.





Peak-to-Average-Power-Ratio Values 





Below is a table of PAPR values for different modulation formats. These can be used in the calculator. 





WaveformPAPR (dB)
Sine Wave3.01
Full-wave rectified sine3.01
Half-wave rectified sine6.02
Triangle wave4.77
PWM signal10*log10(T/dT)
QPSK1.76
8-PSK3.3
π⁄4-DQPSK3
OQPSK3.3
64-QAM3.7
\infty -QAM4.8
WCDMA downlink carrier10.6
OFDM12
GMSK0
Gaussian noise\infty 
Periodic chirp3.01
Peak-to-average-power of different signals [1]










Orthogonal Frequency-Division Multiplexing (OFDM) has a high PAPR of 12 dB relative to a Sine wave with a PAPR of only 3 dB. For a fixed value of EVM, the SNR will be lower for OFDM than for a sine wave.





The table below shows a comparison for 1% EVM





WaveformPAPRSNR (dB)
Sine337
Half wave Rectified Sine634
OFDM1228





References





[1]  Crest Factor on Wikipedia