circuit design till 100MHz

[[email protected]]

Where does this frequency range fall ..in high frequency design or low
frequency design range. For designing the analog circuits till this
frequency, to study the effect of the PCB traces and other circuit
related stuff is there any reference?
thanks.

 

[David L. Jones]

Where does this frequency range fall ..in high frequency design or low
frequency design range. For designing the analog circuits till this
frequency, to study the effect of the PCB traces and other circuit
related stuff is there any reference?
thanks.

100MHz is most certainly "high frequency", and signal integrity in PCB
design will matter a lot.

Dave.

 

[colin]

100MHz is most certainly "high frequency", and signal integrity in PCB
design will matter a lot.

Dave.

these days with such small components,
you can make traces so short,
as long as you have a good ground plane
and with such good low capacitance devices
upto 100 mhz its almost like playing with audio used to be.

depends what you are trying to do of course
and trying to breadboard at 100mhz is a different matter,
ofc theres still plenty of room to get into trouble,
and pcbs do start to exhibit frequency dependant charecteristics at less
than 100mhz if you have long enough traces.
theres lots of old info on that with regard to making wideband 100mhz+
oscilloscope amplifiers etc.

2ghz can be a challenge,
and my laser didnt like being modulated at 2ghz,
ive not gone over 2ghz so far,
unless you include harmonics,
although my simple srd sampling head seemed to show harmonics quite a bit
higher,
I have no idea how acurate it was.

Colin =^.^=

 

[[email protected]]

hi,
i am designing some power amplifiers. i can see most of the capacitor
after few MHz is dominated by its parasitic inductance.Similarly
inductors become capacitors. Transformer is no more an ideal one. the
magentic core also behaves erratic way. Do check the permeability vs.
freq characteristics. Damn,the permeability is flat till only few MHz.
I am looking for some references where these issues are discussed. i
am happy enough if i can design working circuit till 100Mhz. I taked
to these RF people. They just say do not worry yours is not high
frequency, they say for 100Mhz, the wavelength is 3m, so you do not
need to worry much about the hish frquency effects. I am not
convinced. Is there any information regarding this where i can read
more on it.
kristo

 

[Paul E. Schoen]

hi,
i am designing some power amplifiers. i can see most of the capacitor
after few MHz is dominated by its parasitic inductance.Similarly
inductors become capacitors. Transformer is no more an ideal one. the
magentic core also behaves erratic way. Do check the permeability vs.
freq characteristics. Damn,the permeability is flat till only few MHz.
I am looking for some references where these issues are discussed. i
am happy enough if i can design working circuit till 100Mhz. I taked
to these RF people. They just say do not worry yours is not high
frequency, they say for 100Mhz, the wavelength is 3m, so you do not
need to worry much about the hish frquency effects. I am not
convinced. Is there any information regarding this where i can read
more on it.
kristo

I have not ventured into high frequency design, even at this moderate
level, but I found a lot of good information in application note AN47, for
high speed amplifiers, on the www.linear.com website. It is a well written,
comprehensive, and informatively illustrated PDF document. There are also
references to other documents that might help.

Paul

 

[[email protected]]

Thanks Paul. i am desparately looking for more references. I just need
references to read. I want to learn the topic and master it.

 

[Fred Bartoli]

[email protected] a écrit :

hi,
i am designing some power amplifiers. i can see most of the capacitor
after few MHz is dominated by its parasitic inductance.Similarly
inductors become capacitors. Transformer is no more an ideal one. the
magentic core also behaves erratic way. Do check the permeability vs.
freq characteristics. Damn,the permeability is flat till only few MHz.
I am looking for some references where these issues are discussed. i
am happy enough if i can design working circuit till 100Mhz. I taked
to these RF people. They just say do not worry yours is not high
frequency, they say for 100Mhz, the wavelength is 3m, so you do not
need to worry much about the hish frquency effects. I am not
convinced. Is there any information regarding this where i can read
more on it.
kristo

Listen to them again. I don't think they told you you won't suffer from
non ideal components effects, but rather that you won't suffer from
transmission line effects.
IOW, you can consider your PCB tracks as lumped elements rather than
distributed ones. It's not the same thing at all.

As an example, an easily reached 1pF PCB track parasitics is only 1.5k
at 100MHz.

 

[[email protected]]

Thanks Fred. I got your point.Is there any literature on it?
Thanks.

 

[colin]

hi,
i am designing some power amplifiers. i can see most of the capacitor
after few MHz is dominated by its parasitic inductance.Similarly
inductors become capacitors. Transformer is no more an ideal one. the
magentic core also behaves erratic way. Do check the permeability vs.
freq characteristics. Damn,the permeability is flat till only few MHz.
I am looking for some references where these issues are discussed. i
am happy enough if i can design working circuit till 100Mhz. I taked
to these RF people. They just say do not worry yours is not high
frequency, they say for 100Mhz, the wavelength is 3m, so you do not
need to worry much about the hish frquency effects. I am not
convinced. Is there any information regarding this where i can read
more on it.
kristo

If you look at an RF book it will probably go into more detail than you
want,
if you say why you are wanting to use cored transformers we can see if
theres an alternative.
the parasitic inductance of capacitors at 100mhz can be minimised by using
smal value capacitors,
that are physicaly smal too, and very short trace lengths, ie zero length.
aim to make your 100mhz circuit the size of a small postage stamp.

ive resorted to putting SMD capacitors through the hole of a 2 sided pcb
before
to reduce inductance, but thats not realy needed at 100mhz.

it very much depends on what it is your trying to do, ie if its wideband or
narowband.

Colin =^.^=

 

[colin]

I have not ventured into high frequency design, even at this moderate
level, but I found a lot of good information in application note AN47, for
high speed amplifiers, on the www.linear.com website. It is a well
written, comprehensive, and informatively illustrated PDF document. There
are also references to other documents that might help.

Paul

if thats the one I think it is its excelent, its a bit humerous in places
too
gives good advice about grounding, supply decoupling, using short lead
lengths, ground plane,
sheilding etc, conecting scope leads too.

Colin =^.^=

 

[[email protected]]

Thanks colin. Yup i really do not want to goto RF design. Having said
that i also do not want to just design the circuit for low frequency.
Is there an alternative for cored transformer?

 

[Marra]

Thanks colin. Yup i really do not want to goto RF design. Having said
that i also do not want to just design the circuit for low frequency.
Is there an alternative for cored transformer?

Its hard enough getting audio to stay stable never mind megahertz !

 

[colin]

Thanks colin. Yup i really do not want to goto RF design. Having said
that i also do not want to just design the circuit for low frequency.
Is there an alternative for cored transformer?

that depends entirly on what you are trying to do,
but the answer is - probably.

Colin =^.^=

 

[MooseFET]

that depends entirly on what you are trying to do,
but the answer is - probably.

You should also ask your self why you don't want the transformer. You
are likely to be better off using one if you are working with a wide
band signal and need to change impedance levels or split or combine
drives.

 

[[email protected]]

i cannot do wothout transformer. in my application i am using the
transformer to couple the high frequency line into the power lines. i
cannot do without it. But is there is some way to design transformer
without core then it would be wonderful.

 

[colin]

i cannot do wothout transformer. in my application i am using the
transformer to couple the high frequency line into the power lines. i
cannot do without it. But is there is some way to design transformer
without core then it would be wonderful.

I gues you cant, however you can get cores wich go upto 100mhz or more,
micrometals do them.
the higher frequency the smaller the particles its made of but the lower the
inductance too.
guesing your bandwidth isnt that high, you can tune out the undesirable
parasitics.

Colin =^.^=

 

[Rich Grise]

100MHz is most certainly "high frequency", and signal integrity in PCB
design will matter a lot.

Just a nitpick: Technically, 100 MHz is "Very high frequency"; HF is only
3-30 MHz, then VHF from 30-300 MHz, so I'd think either VHF construction
techniques would apply, or broadband, which is even harder. =:-O

Cheers!
Rich

 

[Richard The Dreaded Libertarian]

if thats the one I think it is its excelent, its a bit humerous in
places too
gives good advice about grounding, supply decoupling, using short lead
lengths, ground plane,
sheilding etc, conecting scope leads too.

When I read this:
"We intend to supply useful high speed products and the
level of support necessary for their successful application
(such high minded community spirit is, of course,
capitalism's deputy)."

I almost wept.

Thanks!
Rich

 

[Joel Kolstad]

Just a nitpick: Technically, 100 MHz is "Very high frequency"; HF is only
3-30 MHz

Only to radio operators.

Check out Randy Rhea's book, "HF Filter Design," which details filters up to
something pushing a gigahertz!

 

[MooseFET]

i cannot do wothout transformer. in my application i am using the
transformer to couple the high frequency line into the power lines. i
cannot do without it. But is there is some way to design transformer
without core then it would be wonderful.

What is the voltage of the power line? How much current is flowing?
These will determine the size of wire that must be used for the power
line.

At 100MHz, you can use an air core transformer if you don't need a
wide bandwidth. You want the primary and secondary to be tightly
coupled to each other. Making a twisted pair or using a coax will do
this.

For air core, you need to calculate the inductance you need and then
wind the coax or twisted to yeld that much. You won't want to
resonate with anything less than about 22pF.