#193: Back to Basics: the differential amplifier, aka long-tailed pair, diff-pair
Why Electrical Engineering Stack Exchange recommends it
Electronics Stack Exchange users link it as a gentle explanation of how a diff pair works, both as a recommended intro and as the reference people are following when their own circuits misbehave.
Recommended by 1 people across 1 different months, 2015 to 2022.
What it is
Alan Wolke (w2aew) gives a back-to-basics introduction to the BJT differential amplifier, also called the long-tailed or emitter-coupled pair. He explains basic operation with a simple mechanical simulation, then shows how current sources and current mirrors fix its performance issues and hint at the start of an op amp.
What people said
Strong rec scanny · 2015-10 · Electrical Engineering Stack Exchange · on “Questions on Multi-stage transistor Op-Amp”
This [this video] is a nice gentle introduction to the differential pair amplifier, and he points to how it might be used for an op amp input stage. His other "Back-to-basics" videos are also an excellent way to get started improving your understanding of electronics.
Cites lucenzo97 · 2017-10 · Electrical Engineering Stack Exchange · on “Differential Amplifier BJT Experimenting”
This is a circuit I made recently; a differential bjt amplifier (without any signal, only DC). So I was trying to see, what happens when I change the voltage difference between the base of Q1 and base of Q2. Q3 represents constant current source. According to the example shown here: [this video] , with changing the Vbe drop across Q1, the I_e1 should change inversely proportional to I_e2. As the I_e1 increases, I_e2 decreases. Well, I tried to achieve that, but it didn't happen as said. If 5M potentiometer would be removed, the both of I_e would have a value of approx. 550uA. As I connected the potentiometer into the circuit and changed it, I_e1 was decreasing but I_e2 didn't change a bit (pictur
Cites user312602 · 2022-05 · Electrical Engineering Stack Exchange · on “Does anyone know why this diff amp isn't working?”
simulate this circuit [LINK] – Schematic created using CircuitLab [LINK] I'm new to electronics and I've been figuring out how a diff amp works. I followed a schematic I found on YouTube. Basically, as V3 increases then VM1 should have a voltage drop, while the opposite should happen on the opposite side. At least that's what the YouTube video described. But as you can see in this image, it's not working. What could I be doing wrong? Here's the link to my reference: [this video] And here's the image: [LINK] Here's another simulation. As you can the only voltage change that happens is at output VM1 [LINK] This is the result of the third simulation. [LINK]