Hi Everyone,

While I am reading through the analog switch in diode switching circuits section under diode and rectifiers chapter in semiconductors volume, I have a question on how the low reactance prevents the anode DC voltage from being shorted to ground by the resonant tuning inductor? is the low reactance here the DC blocking capacitor reactance or both resonant tuning inductor and dc blocking capacitor reactance? see the attachment and can someone please clarify that. Thank you.

 

The "digital control" signals usually have current limiting resistances. But the decoupling capacitors already form an AC ground, so the lower end of each inductor already is AC grounded no matter what the DC impedance is through the control signal.

ak

 

I understand that, but can you please explain clearly how the low reactance (compared to parallel LC reactance) prevents the anode DC voltage from being shorted to ground by the resonant tuning inductor?

 

The, "low reactance" of the DC blocking capacitor only means low reactance at the frequency of the circuit. The DC impedance of a capacitor is always nearly infinity. Theoretically, it is infinite, but in reality, capacitors leak a little bit. Medium size aluminum electrolytic caps leak DC in the microamp range. Good ceramic caps can leak DC in the nanoamp range or less.

 

The, "low reactance" of the DC blocking capacitor only means low reactance at the frequency of the circuit. The DC impedance of a capacitor is always nearly infinity. Theoretically, it is infinite, but in reality, capacitors leak a little bit. Medium size aluminum electrolytic caps leak DC in the microamp range. Good ceramic caps can leak DC in the nanoamp range or less.

Thank you, now it makes sense.