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Minicircuits adch-80A+ wideband 10GHZ microwave choke
Minicircuits ADCH-80A+ Microwave Wideband Chokes 50MHz to 10GHz
On offer are several individually priced new ADCH-80A+ Microwave RF chokes from Minicircuits, in cut factory tape.
These are fresh new RoHS compliant devices directly from MCL with a manufacturing datecode of 0810
When biasing RF MMIC amplifiers, the output is a common pin with the power, so some means is needed to isolate the signal from the supply. Biasing via an inductor is the most common approach, because as the frequency rises, the inductor becomes a high impedance and little signal will flow through it, whereas to the DC power, resistance remains low.
However, with conventional wound inductors, there is a 'parasitic' capacitance between the windings and this has the opposite effect, the impedance decreasing with increasing frequency. At a certain point, the parasitic capacitance and inductance form a tuned circuit and the choke becomes resonant and this is known as the choke's SRF, or Self Resonant Frequency.
Unlike conventional RF chokes, these ADCH-80A+ are specially constructed to have extremely low parasitic capacitance, of the order of 0.1pF. This makes them usable in circuits to at least 10GHz, whereas regular inductors are quite unusable at these frequencies. Internal construction is interesting, using two ferrites, one of them binocular and I'm hoping to get some time soon to figure out just how they work their magic.
Note The photos here are of another batch, with an earlier datecode and without the RoHS compliance plus sign. Those for sale here are instead marked as in the table below:
I came across the need for these first in a Silicon Chip article by Jim Rowe, which unlike many is online. The design is for a UHF Prescaler for frequency counters, at http:// .au/cms/A_107676/article.html and one of these chokes is used for biasing an ERA-2SM MMIC. As Jim says ...
This choke is a Mini-Circuits ADCH-80A, a special very wideband device chosen because it has a very low parasitic capacitance and is therefore not self-resonant at frequencies below about 8GHz.
I was then prompted to actually order from MCL to try out the John Miles Comb Generator design at http:// /ke5fx/cg.htm.
He also uses one in his Experimental X-Band Synthesizer design at http:// /ke5fx/hpll.htm
Useful parts, not commonly seen ...
http://minicircuits.com/pdfs/ADCH-80A.pdf
