2.3.5 Relationships Between 1-dB Compression and IP3 Points

Chapter 2.3.5 Relationships Between 1-dB Compression and IP3 Points

Radio Frequency Integrated Circuit Design Second Edition Book
Pages 534
Views 5,872
Downloads : 6 times
PDF Size : 6.8 MiB

Summary of Contents

Radio Frequency Integrated Circuit Design Second Edition Book

  • 26 Issues in RFIC Design: Noise, Linearity, and SignalsThus, the 1-dB compression point can be found by substituting (2.69) and (2.70) into (2.68): 31 1dB3 1dB1 1dB340.89125k vk vk v+= (2.71)Note that for a nonlinearity that causes compression, rather than one that causes expansion, k3 has to be negative. Solving (2.71) for v1dB gives: 11dB30.38||kvk= (2.72)If more than one tone is applied, the 1-dB compression point will occur for a lower input voltage. In the case of two equal amplitude tones applied to the system, the actual output power for one frequency is: 31394oiivk vk v=+ (2.73)The ideal output voltage is still given by (2.70). So now the ratio is 31 1dB3 1dB1 1dB940.89125k vk vk v+= (2.74)Therefore, the 1-dB compression voltage is now: 11dB30.22||kvk= (2.75)Thus, as more tones are added, this voltage will continue to get lower.2.3.5  Relationships Between 1-dB Compression and IP3 PointsIn the last two sections, formulas for the IP3 and the 1-dB compression points have been derived. Since we now have expressions for both these values, we can find a relationship between these two points. Taking the ratio of (2.55) and (2.72) gives 13IP31dB1323 ||3.040.38||kkvvkk== (2.76)Thus, these voltages are related by a factor of 3.04 or about 9.66 dB, indepen-dent of the particulars of the nonlinearity in question. In the case of the 1-dB com-pression point with two tones applied, the ratio is larger. In this case: