transistor as a diode

[electroboy]

This is my first post. Forgive me if there is any mistake. I have seen in current mirror circuit where a transistor is used as a diode . Can anyone please tell me why cant we use actual diodes there instead of transistors..? what is the advantage of using transistor as a diode?
thanks in advance..

 

[keith1200rs]

Without more details my best guess would be matching. In a current mirror it is important that the PN junction voltages match. If you use a diode they won't match.

If you have an example circuit you will get a more accurate answer.

Keith

 

[FvM]

Yes, you can use a diode. To achieve a good current matching, you won't. Think about how a current mirror works and what makes it's performance.

 

[dick_freebird]

Like for like is always the best match.

Diode-connected transistors will have better ideality across
a wider range than a plain diode. That matters a lot to
bandgaps.

 

[syeda amna]

You must know, in current mirrors output current is exactly same as the refrence current. This will only possible if both the transistors have similar characterstics. It is better to use a matched transistor instead of a diode.

 

[electroboy]

thank you all for helping me. These were helpful.