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