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I am in the progress of ordering parts for a LNA board (2.4GHz, based around the broadcom/avago MGA-635P8). I was following the manufacturer's component list in the datasheet for their evaluation b...
The signal comes through a given series resistance (which may be unknown or unseen). Try to select a Farad value which produces an RC time constant covering 3 or 4 AC cycles.
The capacitor charges to a DC voltage and should not vary more than 5 or 10 percent during a cycle, or whatever amount you specify.
If you assume a 50-ohm source then your corner
frequency at the amplifier front end is 50*Cpin
(the blocking cap is a "through" element") and
the cap mainly needs to stay out of the way
(>> Cpin) but you also want some care with
ESL, ESR so that you do not add more poles.
I'd recommend exploring this with some vendor
capacitor models and the declared pin parasitics
if your RFIC vendor makes those available - or put
it to a VNA and take your own port data.
If the part has a vendor eval board available, look
at the BOM. The vendor will not use components
that make their part look bad during evaluation.
If you are not having to use the capacitor as a part of any matching network, i.e. you just need a low impedance then chose one that is series resonant at the operating frequency. Look at the data sheets to find the value. For 5GHz I would guess it will be about 5pF. It will depend on the case size.
If it is a low noise amplifier, <1dB then for the input choose a good quality low ESR capacitor, particularly if you are using it in a matching circuit. You will see an improvement over using a cheap general purpose multi-layer ceramic C.
When I was desiging LNAs I used to use mostly ATC 600 series, there are other manufactures that have very similar performance, we just used ATC to minimise the number of suppliers.
any capacitance where the capacitive reactance is less than 1 ohm would do nicely.
typically, in production, you already HAVE series dc blocking caps that are low cost and that you have previously tested to not resonate in your frequency range. Use one of those
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