cmos pa 30dbm

I am designing an cmos PA for bluetooth . The output power is about 0dBm. But the PA must contain the function of power control. The control range is from -30dBm to 0dBm, and control step is 2~3dB. Now I change the size of output cmos transistor to realize power control. Could you tell me some other good method to control the output power? Could we change the current to control output power? But the output power has no clear function with the current.
thanks.