What kind of circuit is a long tailed pair?
The long tailed pair is a differential amplifier used as the basis of operational amplifier technology – seen with a transistor here it can also be sued with FETs and vacuum tubes / valves. Transistor Circuit Types Include:
How does a long tailed pair with negative feedback work?
The basic long-tailed-pair without negative feedback is shown in the schematic. As the input signal voltage increases, the plate current through the left tube increases, causing the inverted output voltage to decrease because of the increased voltage drop across the plate resistor RL1.
How is gain represented in a long tailed pair?
Accordingly the more accurate representation of gain includes both the differential and common mode elements of the output. One of the developments to the basic long tailed pair circuit shown above, is to use an active current source for the emitter circuit. The basic long tailed pair uses a large resistor in the emitter circuit.
How is bias split in a long tailed pair?
This is where the name “long-tailed pair” comes in. With no differential input voltage (in other words, the transistor bases are at the same voltage) the bias current will be split equally between the two transistors.
Is there any gain in a long tailed pair?
In reality, there is always some gain from common mode signals. Accordingly the more accurate representation of gain includes both the differential and common mode elements of the output. One of the developments to the basic long tailed pair circuit shown above, is to use an active current source for the emitter circuit.
Why are long tail resistors used in integrated circuit?
The resistor has a high value and as a result it resembles a current source. In many integrated circuit applications where further transistors can be added very easily, the long tail resistor is often replaced by an active current source to improve the performance.