Для согласования каскадов, повышения входного и понижения выходного сопротивлений.
Хоть стоковый, (на полевом) , хоть эмиттерный (на биполярном) транзисторах повторитель предназначен для согласования каскада с высоким выходным сопротивл. с каскадом с низким входным сопр. Это усилитель с коэффициентом усиления меньше единицы.
Все же истоковый повторитель.
t is commonly known that IC, even if those belong in the same family, do not always interface themselves with a single wire. There come times that ICs from different families of with different power supply, needs t be interfaced somehow. TTL for example are powered with 5V and CMOS can be powered with 3 to 15 Volts. Also, the high and low states of TTL and CMOS are not the same. Another common example is when one output of an IC needs to be interface with multiple inputs of other ICs.
In such (and many more cases), to ensure proper and stable operation, interfacing methods should be taken into consideration. Find bellow the most common (and hard working) methods to interface ICs together, ICs that may belong to different families with same or different power source/voltage.