OpAmp with gain switch

Many times it is necessary to switch the gain of an operational amplifier, transforming an inverting stage to non-inverting or the other way around. This is useful in front-ends, analog signal conditioning, modulators, choppers and almost mandatory in audio systems, where signal phase inversion can be requested by the user

RF switch using BJT transistor

In the search for a cheap way to make RF switches in homebrew projects, I came with the idea of using a NPN transistor biased as two separated diodes. The idea consists in the use of two opposed diode junctions to block de RF signal when the controlling voltage is