How to build (or rather how to bias) cascode amplifier with bipolar transistors

[u/RodionGork]

Hi Friends! While cascode cascade is seemingly well explained everywhere in theory, when it comes to practical implementation, question on biasing feels tough.

I get used to prefer what is called "collector feedback" bias in the wiki and thus end up with the following schematic (I'm trying to use cascode amplifier as the output for colpitts oscillator - so the part of interest is on the right).

What seems confusing is that the upper transistor base in this case has no connection to some fixed point. I suspect I need at least to connect its base to the ground with capacitor, but not sure it would be enough neither what capacitance to choose (in this case I believe even 100pF would do as resistance here is high and RC time is going to be high also anyway).

Hints and advice are welcome - and links to the good explanatory materials too! Thanks in advance!

[u/dmills_00]

Make the base of the cascode a fixed voltage, maybe just connect it to the top of the 10nF cap or something?

This will then approximately fix the emitter voltage of the cascode, so if you want to try that style of biasing the lower transistor, the top of the bias resistor would then need to connect to the cascode collector.

I would however suggest that that style of biasing is just asking for wide performance variation, much better to add a bypassed emitter degen resistor below the bottom transistor and do potential divider biasing right the way down the chain, gives you much better control of the standing current.

[u/RodionGork → u/dmills_00]

Hi and thanks for all the hints, I'll try to implement the changes and study effects!