Hello,
I'm using the MRFX1K80H 175 MHz reference circuit, with a 60V drain voltage.
With a network vector analyzer I measure the propagation delay of this amplifier (+ an 1000 W attenuator at the output, of course !), and I see that for low to medium output power, let's say up to 20 W approximately, the propagation delay is quite stable. But when I increase the input power in order to increase the output power above 20 W, the propagation delay varies a lot, and even after waiting for 1h in order to stabilize the temperature of the amplifier (+ its heat sink) the propagation delay is still having some significative variations.
For my application I need a constant and stable propagation delay. The group delay is not a problem since I can perform a calibration at the start of our system, in order to compensate it, but the propagation delay can't be compensated in our system if it's varying too quickly.
So I wonder how can I stabilize the propagation delay, in order to make it constant with time, within a few ns ? Are the propagation delay variations due to thermal considerations ? I have to say that I don't use any type of control circuit to control the temperature, gain or output power of the amplifier: I just adjust the quiescent biasing current to 100 mA approximately with the potentiometer of the reference circuit at startup, and then apply the RF signal at the input.
Thanks in advance for the help you can provide, and best regards,
Antoine
