The increasing number of the power levels is achieved by using {HEAD ~ electrical elements}, such as {TAIL ~ resistors}, transformers and others 
such as
The increasing number of the power levels is achieved by using { HEAD ~ electrical elements } , such as { TAIL ~ resistors } , transformers and others
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH