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In a receiver, for wideband (10-150MHz) biasing of a MMIC amplifier using
inductors between the RF trace and the power rails, I'm finding that a single inductor tends not to work so well due to (1) wanting a largish inductor (say, one with 500 ohms of reactance at 10MHz in a 50 ohm system -- 8uH) but (2) not going beyond the self-resonant frequency of the inductor, which of course is smaller the larger the inductance (that 8uH inductor might typically have an SRF of 50MHz, noticeably below the 150MHz I'm trying to achieve RF blocking to!). Is there a better means of providing wideband DC biasing/RF blocking than just placing a large and small inductor in series? I've run SPICE simulations of this, and -- just as when you stack multiple capacitors in parallel for wider RF coupling -- there are significant anti-resonances that drop the overall reactance of the pair of inductors to much less than 500 ohm (even less than 50 ohms!) unless you're very careful in the choice of individual inductor SRFs, inductances, etc. Thanks, ---Joel Kolstad |
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