Biasing of diff pair.

[paulmdrdo]

What's the benefit of biasing the input diff amp shown in red? Also I want to understand the benefit of placing the device in green area. I know it's a floating current source but what benefit do we get from it? Thank you!

 

[sutapanaki]

Well, the benefit of biasing the diff pair in red is that it can't work without being biased.
The devices in red set the quiescent current in the output stage.

Sorry about the typo - devices in green set the quiescent current in the output stage.

 

[paulmdrdo]

Good day to all. I'm doing a self study about the circuit shown above. I kind of don't understand which structure biases the differential pair(red). The explanation I read from the book that it is the structure in green that biases it, but the lecture I'm following says it it's the structure in blue that biases the diff pair. Which one is true? Please bear with me my command of english language is not that good. Thank you.