FETS on outputs of op amps or gates

[ParkerMike]

What does these FET's do on the outputs of op amps or logic gates?

The output of the op amp or logic gate will enable the FET, but what is the FET used for? and without the FET what would it change?

 

[chuckey]

The FETs are used as switches when the gate goes +, a short appears between G and D, else its a very high resistance.
Frank

 

[stanleystan]

The FETs are used as switches when the gate goes +, a short appears between G and D, else its a very high resistance.

Yes, I understand this, but what I don't get is why? without using the FETS what would be the difference?

Removing the FET would do what? and adding the FET in the circuit is having what advantage?

 

[chuckey]

If there was no FET the circuits connected to the drain and source would never be connected tto gather.
Frank

 

[FvM]

The JFETs in the schematic snippets are working in different roles, analog switch, rectifier diode, some possibly as buffer.

Generally, it's quite difficult to analyze the exact function of similar circuits "bottom-up", without knowing the overall function and involved waveforms, even with a good foundation in analog circuit design. The circuit analysis must be at least supported by a "top-down" approach, identifying the principle function of each block and the related signal pathes.

We have seen a large numbers of similar schematics in previous Edaboard threads, e.g. from former member danny davis. In my view, it was rarely possible to get much insights.

 

[Audioguru]

We have seen a large numbers of similar schematics in previous Edaboard threads, e.g. from former member danny davis. In my view, it was rarely possible to get much insights.

I agree that this is "Danny Davis" back again since the very old schematics are scanned and the ICs are also very old.

 

[ParkerMike]

Are the FETS used to as a discharge path?

When a Logic gate is in the low stage, is it true that even in the low stage a capacitor can't discharge into the output pin of a logic gate or op amp?

Internally inside the logic gate or op amp it can be high impedance even in a low logic state on the output pin?