Consider the following differential amplifiers:

In the first picture, we have a basic differential amplifier configuration and we can assume that it's symmetrical (meaning M1=M2 and resistances are the same).

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In the second one, we replaced the resistances with diode-connected PMOS transistors acting as active loads to the NMOS transistors. Since they're connected in diode mode, they enter saturation as soon as they conduct.

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My question is, what are the advantages and disadvantages of these two configurations? The second one is obviously used in integrated circuit configurations, but when we observe them generally, how does the active load configuration act differently from the passive load configuration?


1 Answer 1


Don't have enough reputation to comment so leaving it as an answer.
1. Diode connected loads are easier to implement and takes less space on ICs
2. Gain is independent of gm as it's just ratio of W/L of input and load fets
3. The one big downside is the extra headroom required for diode-connected loads


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