Increase in intermodulation products of the power LDMOS A3T09S100N

[KDan]

Our question relates to the A3T09S100N LDMOS transistor. We used it in a power amplifier that amplified a 256 QAM modulated signal (PAPR 7 dB). The average output power was 37 dBm. To test the reliability of the amplifier, we left it in this mode for 14 days. The temperature of the transistor case has been stabilised at 110 degrees Celsius. The measured difference between the initial and final values of the adjacent channel power ratio (ACPR) was 5 dB. How can we explain this deterioration in the transistor's linear characteristics, which we measured repeatedly?

Best,

Karel

[ErikaC]

Hello,

Have you checked the A3T09S100N RF Power Electromigration MTTF Calculation Program to check all the parameters involved?

[KDan]

Hello ErikaC

Yes, we have checked this. I also looked at the Black's equation itself, although I only estimated its coefficients. We have even tried to overestimate the critical input values in order to have a reserve in the calculation. Frankly, there is no evidence of discrete failures, the DUTs are still in good working order. Basically, we only noticed a slight deterioration in the intermodulation distortion, as evidenced by the ACPR dropping from 57 dB to 52 dB. Since the ACPR parameter is the key for us, we need to know the mechanism of this change. To be honest, we are not 100% sure that the degradation is caused by the transistor under test alone. But we think it is very likely.

[KDan]

I forgot to enter the frequency band in which the test took place: 900 MHz to 960 MHz

The greatest ACPR degradation, the aforementioned 5dB, was observed near the top of the frequency band.