Why does the evalboard layout have small rectangular copper areas near C1 and near the amplified RF output? These copper pads are not hooked up to anything so I am not sure what they are for.
(pics of the evalboard copied from the datasheet:) "
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Why is the input RF signal narrowed down after C1?
The datasheet specifies an input VSWR of 2:1, not sure what effect that has on the layout.
Also this chip requires a gate voltage input of about -1.2Volts (-0.6V to -2.0V min/max specified). Is this voltage ok to just be in the min/max range or does it require precision? I was thinking of generating this signal with a small cap switcher IC.
I figured I might as well do a layout for this MMIC, before trying a transistor based amplifier.
Probably so that you can put some copper foil on them and a blob of solder to join them up to the track with the signal on it, as a sort of stub, to alter the impedance match. It tends to indicate that they weren't really confident that it would be matched up properly when they built it for the first time. That is understandable, it isn't easy to get right first time.
This narrow section is the two transmission lines T1 and T2, which have a higher impedance than the wider section. Wherever you put C2 is the place which defines where T1 ends and where T2 starts. That's what I reckon anyway.
No idea. You might want to try different voltages to see if it affects gain, linearity, efficiency, etc., then you will know if it is important or not. If you're lucky, the manufacturer will provide you with curves showing these effects so you don't have to do the experiment.
If you use a switching converter to generate supplies for this IC, be aware that any ripple on the supplies might end up modulating the output signal (e.g. AM) which will produce sidebands at an offset from the carrier equal to the ripple frequency (and perhaps harmonics thereof), and this might interfere with other things, though in the ISM band you are relatively safe. E.g. if you use a 1MHz switched-mode converter, and you transmit at
2450MHz, you could expect to see something at 2451MHz and 2449MHz.
I expect that it would be hard to do better than a MMIC at these frequencies. If they will give/sell you some parts then this sounds great. Don't cook yourself!
Sounds reasonable to me! :) Also does C2 act as part of an LCL lowpass filter? I was wondering why you need C2 at all? I am tempted just to run a straight 50ohm trace from the input connector to the chip with just the AC coupling cap..
Ok, I will make sure to filter that signal down to a couple uV noise floor.
I don't think I need to worry about that unless I use a high gain antenna pointed at my head. :)
probably one of the following in order of decreasing respectability to make the input look more like 50 Ohms resistive, to make the gain or output power greater in order to boast about it to stop it from oscillating (if it is a shonky design)
They must not of had an ARRL UHF/microwave experimenters manual :) I got mine in the mail a couple days ago.
Figure 16 on Page 6-15 looks very interesting, it shows 8 different impedance matching circuits. I still don't know how to pick which one of the 8 to use (yet) but it looks cool. :)
If the input impedance is badly mismatched, the power gain may appear low because the input power is being reflected back to the source. If the matching is improved, this can make the measured gain increase (when all measurements are made with the same source impedance).
That would be unlikely with a non-resonant circuit like an RC. It increases the dissipation in the resistor before the C and drops the gain. If you had LC that would be another story.
OT: I have seen you on a German NG. How did you learn that language? From the quality of your posts there it can't just be from a few years in school. Did you live there?
Well, in that case it would probably fall under the category that you had called "shonky design" ;-)
Yeah, they are now Infineon and I am not so fond of them anymore. Excellent products but their customer support, well, let's not go there.
Your German does look good and is easy to read. Don't worry about adjective endings and stuff like that, even Germans get those wrong at times. Also, they all understand English pretty well. Except when they travel to the US and then hear Archie Bunker on TV "I ain't gonna have none of this no more at this here table ...".
I think at 2.4GHz, pretty much everything looks like a combination of R, L and C, in proportions which are not easy to determine, let alone influence in the desired direction.
That's very kind of you to say so, but I know my German isn't that good. I studied it in school for quite a few years but I was quite lazy and didn't learn nearly as much as I should have. In '97 I spent 3 months doing work experience in Munich (with Siemens semiconductor group as it was then). In spite of these opportunities I never learnt which adjective ending to use when, and my grammar remained very bad. Since then, I have been slowly forgetting what little I knew and now I resort to the dictionary for several words in most sentences.
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