Can phase noise and P1dB problems be caused by mismatching?

[buyan]

phase noise and P1dB

To design a power amplifier, there are a few amps cascaded to form the drive stage and then followed by power FETs.

From the specification, the last FET's P1dB is 41dBm, but I cannot get it. Is this due to the stages mismatching?

If I do some tuning, the P1dB can be got with sacrifice of phase noise. I am wondering whether the phase noise problem and P1dB problems are both caused by mismatching. If not, what are the possible reasons?

Thanks for help in advance.

 

[flatulent]

Re: phase noise and P1dB

Phase noise is the phase modulation of an oscillator by noise. The P1 is the result of the basic nonlinearity of the active device or running into the power supply voltage. The latter is related to the load impedance presented to the active device output. The phase noise of an oscillator several stages previously in the signal path is not affected by this impedance. In fact, the phase noise would not be affected if the signal path included a limiter.

 

[footprint]

Re: phase noise and P1dB

To design a power amplifier, there are a few amps cascaded to form the drive stage and then followed by power FETs.

From the specification, the last FET's P1dB is 41dBm, but I cannot get it. Is this due to the stages mismatching?

If I do some tuning, the P1dB can be got with sacrifice of phase noise. I am wondering whether the phase noise problem and P1dB problems are both caused by mismatching. If not, what are the possible reasons?

Thanks for help in advance.

which FETs did you choose for your PA?

 

[buyan]

Re: phase noise and P1dB

Hi, footprint, I cannot remember the exact model No. now. It is from Mitsubishi.

BTW, will this affect the performance?

Added after 7 minutes:

Phase noise is the phase modulation of an oscillator by noise. The P1 is the result of the basic nonlinearity of the active device or running into the power supply voltage. The latter is related to the load impedance presented to the active device output. The phase noise of an oscillator several stages previously in the signal path is not affected by this impedance. In fact, the phase noise would not be affected if the signal path included a limiter.

Thanks a lot.
If there is a mixer, inputs are LO and IF, output is RF. Then the phase noise of the output RF signal is only determined by the LO's performance?

Normally what factors will degrade the output's phase noise?

 

[cjg40]

Re: phase noise and P1dB

the phase noise index is F = F1+(F2-1)/G1+..........+(Fn-1)/G1*G2*......G(n-1),so it is mainly determinded by the first stage.

 

[BigBoss]

Re: phase noise and P1dB

the phase noise index is F = F1+(F2-1)/G1+..........+(Fn-1)/G1*G2*......G(n-1),so it is mainly determinded by the first stage.

This is not Phase Noise... :sm31: It's Friis formula to calculate Noise Figure of Cascaded stages..

To predict Phase Noise of a VCO (or simple OSC) we ha ve to use Leeson formula that is found in every MW book..

 

[elkimhoc]

Re: phase noise and P1dB

:spoko:
That right Big Boss, but Leeson formula is for one stage transistor, to predict the phase noise for cascade stages you must use softwares like ADS or ohters