quiescent current
my power amplifier's IMD is very bad when i test it at low temperature(below zero),but at 55(high temperature),its performance is the same as the normal temperature,it is good.
i use the the diode to compensate the temperature drift.
so i decide to use the DS1870,it sample the Idq and regulate the Vgs of the LDMOS. and an engineer tell me the Idq is not change when the circument temperature is not change. but when test my power amplifier,i find ,at the same temperature,the Idq change with the input rf power!
i want to know what is the right answer![/u]
It is correct that the quiescent current can change with RF input/output power. When driven increasingly strong, we make a transition from class C amplifiers to switched amplifiers (D,E, ...) Then the load impedance becomes very important.
But the truth is that you usually will not have to deal with this problem. Power amplifiers are used in transmitters before the antenna. So you have full control over the RF input and output power!
If your design is a linear PA, the input power shall not influence too much the Idq (quiescent current) because it will increase the gain expansion (different gains for different input powers). Usually in a multistage Linear PA design, at least the first stage shall be in A class.
If your design is not a linear PA, things are different.
Is normal to compensate the temperature using a diode.
my PA is the WCDMA pa,i have to deal with the temperature drift,but the diode compensate the LDMOS very well from the room temperature to 55,but below the zero,this circuit is very bad,what shall we do