Bridge Circuits

What is Bridge Circuits ? Why do they called so? Discuss about them.

The Long-Tailed Pair (LTP) Circuit

• The term 'long-tail' came from the fact that the large resistor connecting the emitters of the transistors to ground or a power supply resembles a long tail. 
• In Figure, wherein NPN transistors are used to form the pair, this resistor is tied to ground.  
• The long tail actually functions as a current source, and may in fact be replaced a more elaborate 'active' current source circuit.