Matched RF amplifier sections...to modularize or not to modulize
Matched RF amplifier sections...to modularize or not to modulize
(OP)
Hey all you smarter than me RF people! I am assisting in the developement of broadband circuitry and keep insisting on building discrete RF amplifier/ attenuator modules that can be attached to a main circuit board. We are having some problems with our current configuration consisting of the amp/attenuators built onto the main PCB. Because of minute differences of the components, caps, resistors, amps, solder amounts and other devices, it is very difficult to obtain a similar response across the octaves of desired bandwidth. There are four RF strips on each main board that are combined and compared. I keep harping on discrete rf sections so the responses of each can be swept and matched and then installed onto a main PCB. It is extremly important that the response of each of the four amplifier sections be as close as possible within 0.5dB. It does not matter how lumpy and bumpy the response is just as long as all four amp sections are the same. Just because an amplifier section is copy and pasted to the PCB in the design phase does not mean all four will be of the same response. Them Minicircuits amplifiers are good but not all exactly the same....the same part number of course.
Sooooo, does modularizing the RF sections make sense to anyone or am I barking up the wrong tree? I need the response to be better than 0.5dB difference across 3Ghz of bandwidth.
Thanks & 73,
Rob
WD4DUI
Sooooo, does modularizing the RF sections make sense to anyone or am I barking up the wrong tree? I need the response to be better than 0.5dB difference across 3Ghz of bandwidth.
Thanks & 73,
Rob
WD4DUI





RE: Matched RF amplifier sections...to modularize or not to modulize
within .5 db for this BW.
Can you get around it somehow ? ( e.g. valibration )
<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032
RE: Matched RF amplifier sections...to modularize or not to modulize
Don't forget to test over temp.
You may want to try adjusting phasing from one amp to another to see the effect. That can change the shape of the curves.
Good luck,
kch
RE: Matched RF amplifier sections...to modularize or not to modulize
Digital control is also possible, many companies have digital attenuators with 0.5 dB step sizes (not quite good enough for your app), but Hittite just released a part with 0.25 dB step which may work for you. HMC539LP3 is a 3mm x 3 mm, dc-4 GHz, 5 bit, 0.25 step. I just ordered one to evaluate for an interference cancellation system i'm working on (hasn't come in yet). Also you don't mention phase match requirements, but be aware that there will be a phase difference for different attenuations.
Peter
RE: Matched RF amplifier sections...to modularize or not to modulize
RE: Matched RF amplifier sections...to modularize or not to modulize
Whenever I see these type of extreme specs, my first inclination is to go back upstairs.
Go and revisit the system design. What caused this requirement? Is it based on accurate assumptions? Do you really need .5 dB? Maybe you really need +/-2dB.
That may be the easiest thing to do.
Just go and correct the original requirements.
groundhog1
RE: Matched RF amplifier sections...to modularize or not to modulize
It is not clear what your frequency range is. "3 ghz bandwidth" does not tell us much.
RE: Matched RF amplifier sections...to modularize or not to modulize
Measured the return loss of the first amp (ERA-3) and was not very good, anywhere from -15 to about -5 Db, now know the mini circuits amps are not great. At least this version of the board does not oscillate....that's another story.
Thanks for all the advice!!!
73
Rob
WD4DUI
RE: Matched RF amplifier sections...to modularize or not to modulize
htt
It has a nice grounded bottom package, so the package parasitics will be repeatable. Also, it has operation to 6 GHz, so it will be more repeatable up to 3 GHz. I would print on the bias structure, using only a chip resistor, to make the bias line as repeatable as possible. And I would be sure that all the amps I bought came from the same production lot number.
RE: Matched RF amplifier sections...to modularize or not to modulize
Thanks for the info on the Hitite amps. We have already built the boards using the ERA-3 amps. As I stated before, I think the PCB has problems as the resulting response of the RF path is ugly. I jumped an unpopulated board and swept the thing. UGLY!!! Either the board house did not build to our specs or our specs (trace widths, ground plane distance, wrong board material (FR4) and other determinants) are wrong. I have to figure out how to "flatten" the responmse of our present boards if that is even possible. This is reason for my orginal post. If all the stages were modularized and connected via coax and appropriate connectors, then we could sweep each stage seperately and make corrections to our layout. It would be less costly and certianly easier to determine where the impedance bumps are occuring.
I had a nice full head of hair before I started this; and now? Getting thinner by the hour.
Please....more advice.
73
Rob "flatter is better?"
WD4DUI