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I need to design an RF amplifier with high gain. It seems every RF book teaches cascading, but not cascoding. Is there a disadvantage to cascoding? It seems like we don't need to match impedances with cascoding, making our lives easier.

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    \$\begingroup\$ Cascodes are pretty common for high frequency bands (10 - 40 GHz). Often the parts are sold as "travelling wave" amplifiers rather than cascode amplifiers. \$\endgroup\$ – The Photon Mar 2 '15 at 17:05
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    \$\begingroup\$ They are also popular at HF (like 1-30 MHz), and in IF amplifiers. \$\endgroup\$ – Leon Heller Mar 2 '15 at 19:57
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You do need to match input impedance with cascoding because the emitter, as an input can be very low (circa 10 ohms or less). Also, RF amplifiers do tend to use cascode configurations and I've certainly designed a cascode input in a couple of designs. I'm thinking of professional metal detection products, radios and photodiode amplifiers.

It seems trite to mention the disadvanges because these are largely down to the circuit not being applied for the right reason so, the main advantage is the first transistor's miller capacitor has very little effect (no negative feedback) because the collector is held constant by the 2nd transistors emitter.

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I think cascode is great .I use a MPF 102 JFET on the bottom and a BJT on the top . When the supply volts is 12V I use a BC547 for the BJT . For higher supply voltages such as found in Valve radios I use MJE 340 on top . It has been stated that a disadvantage is the need for a higher supply voltage .This can be got around by inverse cascode or other schemes .I have run inverse cascode with MPF102 and BC557 for a 6V supply . In the old days the need for two devices was a drawback due to cost .This just is not true anymore.

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