Hey guys
What's this circuit? look:

Why the designer has used two the same MOSFET with the same resistor? I mean coundn't the designer design the above circuit like this?:

 

@booboo
In your second picture, the output is high when input is low.

In the first picture, the output is high when the input is high.

 

Of course the noninverting amplifier probably could have been made with a single common base circuit

 

@booboo
In your second picture, the output is high when input is low.

In the first picture, the output is high when the input is high.

Ah-ha! then it is a logic level-shifter. 5v to 3v3

 

Ah-ha! then it is a logic level-shifter. 5v to 3v3

I guess it could be but, 5V in to 3V out. But, as drawn and not knowing exactly what the rest of the circuit does, I would say that
- one is an inverting buffer (bottom),
- one is a non-inverting buffer (top).

 

Here is a link to a discussion of bi-directional level shifters: http://www.adafruit.com/datasheets/an97055.pdf (actual creator was Philips AN97055). This is a more practice-oriented example: https://learn.sparkfun.com/tutorials/bi-directional-logic-level-converter-hookup-guide

John

 

Here is a link to a discussion of bi-directional level shifters: http://www.adafruit.com/datasheets/an97055.pdf (actual creator was Philips AN97055). This is a more practice-oriented example: https://learn.sparkfun.com/tutorials/bi-directional-logic-level-converter-hookup-guide

John

I never seem to have a need for bi-direction level shifter. One direction has always been enough. It is an interesting metal challenge but in practice, an output drives an input. The output rarely switches to become an input and input becomes an output to necessitate a bi-directional level shifter.

 

How about in an I2C bus? Clearly, Philips and Sparkfun felt there was a need. And a bidirectional bus can be use one-way too.

John

 

How about in an I2C bus? Clearly, Philips and Sparkfun felt there was a need. And a bidirectional bus can be use one-way too.

John

If SparkFun is the seller, then the application will likely be some older/cheap/through-hole device communicating with an RPi.

 

The circuit may have been implemented for level translation.

 

Two MOSFET are used to block the voltages in both direction by allowing by directional current flow.