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Design >> RF Design >> a problem in Doherty Power Amplifier.
https://designers-guide.org/forum/YaBB.pl?num=1244700012

Message started by waseda-rfic on Jun 10^th, 2009, 11:00pm

Title: a problem in Doherty Power Amplifier.
Post by waseda-rfic on Jun 10^th, 2009, 11:00pm

the peak amplifier in Doherty PA should exhibits a high output impedence when it is off. but i find it hard to make it has a high output impedence. anyone has some experiences?

Title: Re: a problem in Doherty Power Amplifier.
Post by pancho_hideboo on Jun 11^th, 2009, 12:46am

Hello, keio-rfic.

Try to use techniques such as active cascode connection or cascode bootstrap in cascode amplifier.

K.Bult and G.J.G.M.Geelen:"A Fast Settling CMOS Op Amp for SC Circuits with 90dB DC gain", IEEE JSSCC, vol.25, no.6, Dec. 1990.

Title: Re: a problem in Doherty Power Amplifier.
Post by waseda-rfic on Jun 11^th, 2009, 7:19pm

pancho_hideboo wrote on Jun 11^th, 2009, 12:46am:

Try to use techniques such as active cascode connection or cascode bootstrap in cascode amplifier.

thanks for your help again. active cascode and cascode bootstrap can increase the output impedence in low frequency. but i am not sure it is also effective in RF frequency as in 5 GHz? i see in the paper .they mainly use offset line or match network to increase the impedence. but in my simulation, i find hard to satisfy both load line and high output impedence using match network. so i want ask which is better for improve the impedence?

Title: Re: a problem in Doherty Power Amplifier.
Post by waseda-rfic on Jun 11^th, 2009, 7:48pm

pancho_hideboo wrote on Jun 11^th, 2009, 12:46am:

Try to use techniques such as active cascode connection or cascode bootstrap in cascode amplifier.

Title: Re: a problem in Doherty Power Amplifier.
Post by pancho_hideboo on Jun 15^th, 2009, 1:19am

keio-rfic, don't do duplicate posts.

The following two are completely same.
http://www.designers-guide.org/Forum/YaBB.pl?num=1244700012/2#2
http://www.designers-guide.org/Forum/YaBB.pl?num=1244700012/3#3

waseda-rfic wrote on Jun 11^th, 2009, 7:19pm:

active cascode and cascode bootstrap can increase the output impedence in low frequency.
but i am not sure it is also effective in RF frequency as in 5 GHz?

It is effective. But it is not effective for capacitive component of output impedence.

waseda-rfic wrote on Jun 11^th, 2009, 7:19pm:

i see in the paper. they mainly use offset line or match network to increase the impedence.
but in my simulation, i find hard to satisfy both load line and high output impedence using match network.
so i want ask which is better for improve the impedence?

Both cascode amplifier and reactive impedance transformer using discrete LC or distributed lines are needed.

Title: Re: a problem in Doherty Power Amplifier.
Post by waseda-rfic on Jun 16^th, 2009, 2:18am

HI pancho_hideboo
thank you for your reply. I got it!!!