calculating a quatre-wave transformer

[Philip Newman]

operating at 34GHz, I am trying to design a quater-wave transformer like so

Ideal T-Line------------------------------- Inuductor of 2nH--------
|
|
grounding
|
Capacitor
Drain
0.1pF
Supply 2.5 V
|
|
|
ground
ground

For the idea transmission line, i need to find out the impedance and the
electrical length, in degrees.

The idea of this is to replace an inductor with a section of transmission
line, as this is easier to implement in microstrip. It is part of a biased
transistor circuit. I cannot find the necessary equations to implement
this,

Any help would be most appreciated

Phil

 

[Baphomet]

operating at 34GHz, I am trying to design a quater-wave transformer like so

Ideal T-Line------------------------------- Inuductor of 2nH--------
|
|
grounding
|
Capacitor
Drain
0.1pF
Supply 2.5 V
|
|
|
ground
ground

For the idea transmission line, i need to find out the impedance and the
electrical length, in degrees.

The idea of this is to replace an inductor with a section of transmission
line, as this is easier to implement in microstrip. It is part of a biased
transistor circuit. I cannot find the necessary equations to implement
this,

Any help would be most appreciated

Phil

There is an equation for the impedance looking in to a terminated
transmission line which is as follows:

Zin = Zo * (ZL + jZo * tan(Bl))/(Zo + jZL * tan(Bl))

Zin is the input impedance, Zo is the characteristic impedance of the
transmission line, ZL is the load (termination) impedance, and Bl is the
length of the transmission line, in degrees (or radians) of the frequency
of interest. In our case, Bl is so small that we can assume the tangent
term is zero. So the whole thing reduces to:

Zin = ZL

posted by Mac 10/31/2003

 

[Philip Newman]

so, in this case, is ZL (load resistance) the real part of the lumped
element resistance (is finding the complete impedance of the inductor and
capacitor, r+jx)?

 

[Baphomet]

so, in this case, is ZL (load resistance) the real part of the lumped
element resistance (is finding the complete impedance of the inductor and
capacitor, r+jx)?

Maybe Mac will answer. He's a lot smarter than I am ;-)

 

[Philip Newman]

its ok, i think i have it sorted. i managed to find an ADS template from my
lecturer that was used. basically used a smith chart to get the angle to 0
by varying the electrical length, E, using Z as 75 ohms, at 8.5 GHz (1/4 of
34).

put that TLin in instead of the inductor, and it worked!! the peak is
slightly off at 33.9Ghz, but can always optimise to acheive the correct
peak.

cheers for the help though

phil

--
Philip Newman

"There was never a time when you or I did not exist.
Nor will there be any future when we shall cease to be."
(Krishna to Arjuna in the Bhagavad-Gita)

 

[Mac]

its ok, i think i have it sorted. i managed to find an ADS template from my
lecturer that was used. basically used a smith chart to get the angle to 0
by varying the electrical length, E, using Z as 75 ohms, at 8.5 GHz (1/4 of
34).

put that TLin in instead of the inductor, and it worked!! the peak is
slightly off at 33.9Ghz, but can always optimise to acheive the correct
peak.

cheers for the help though

phil

Glad you got it sorted. I was going to suggest using a Smith chart,
actually. ;-)

By the way, for me this is all book-learning. That is, I have no practical
experience actually building RF stripline and microstrip circuits. I just
have relevant course work and text books. ;-)

I would recommend, if you want to invest in a book, _Microwave
Engineering_ by David M. Pozar. I have the second edition. It is more
practical than academic.

good luck.

Mac
--

 

[Philip Newman]

already got it!! it all seemed a bit too much for me though (if only there
was a simple solution for everything!). this is all text book work for me
too, but hope to put it in practice soon!!

cheers

phil