Increasing the IP3 of the MAX2659 Low-Noise Amplifier (LNA)
While the linearity of the MAX2659 is more than sufficient for most applications, it is possible to improve the device's IP3. This can be accomplished by adding a degeneration inductor between pin 2 (the amplifier's emitter) and ground, as shown in Figure 1. While this addition increases IP3 significantly, there is a trade off: the gain will reduce and the noise figure will degrade slightly.
Figure 1. Typical application circuit for increased linearity.
Using a 0.9nH inductor provides a good balance among linearity, gain, and noise figure. Measured results are shown in Table 1. Of course, a different value inductor can be used if more or less linearity is required, although gain and noise figure will change accordingly.
Table 1. Performance of the MAX2659 With and Without a Degeneration Inductor
|Degeneration Inductor||ICC (mA)||Gain (dB)||NF (dB)||IP1dB (dBm)||IIP3 (dBm)*|