Difference between upper frequency and lower frequency in ACPR of CDMA PA

When testing the ACPR of CDMA PA, the difference between upper frequency and lower frequency was a little big. For example, the amplitude of +750KHz was -46.6dBc, while that of -750KHz was -49.9dBc.
But normally, these two value were almost same. Could you tell me what would cause this and how to avoid? Many thanks.

Are they necessarily balanced?

The overall distortion at ACPR is a vector sum of the distortions generated by the third and fifth order nonlinearity (IM3 and IM5).

The cause of ACPR asymmetry is most likely the phase difference between the IMD products due to separate AM-AM and AM-PM device mechanisms.

So, the bias point of the active device mainly dictates ACPR asymmetry

If the ACPR test pass successfully on both sides, probably doesn?t matter if the spectrum is asymmetrical.

Because the CDMA is like a mulitone signal it is not neccesary to have a symmetric ACPR; and it is common in practical applications.

Hi sunstar16,

Check the power supply! Ensure impedance of the power supply is as low as possible DC to some MHz. Assume, only single channel is being amplified, you have to make sure impedance at drain, gate is as low as possible from 0 to 1.3MHz. Also, you can demonstrate the asymmetry phenonmenal by injecting two tone into your system, by keep increasing the tone spacing, the asymmetry can surely be observed! The asymmetry is bacause of the IMD originated from the envelope signal.


Mesfet+

memory effect

Check if the ACPR before the CDMA is symmetric. Possible the upconversion path have differencies between lower and upper sideband.