I have designed and built a few things that worked. But I always used the   
   sledge hammer approach when it comes to impedance. I made the output impedance   
   of the stage much lower than the input impedance of the next. Upon further   
   reflection, I think that    
   sometime this is a waste and actually may be not all that effective.    
      
   These are the the throes of an almost old Man so don't tear me up.    
      
   I have known for a long time that the input impedance of a bipolar common   
   collector stage is Re times hfe. But what about the common emitter stage ?    
      
   I have surmised that it is the same. Though lower, it is because of the   
   selection of a lower value resistor to keep the voltage gain up. But as long   
   as it operates in its linear region and that collector current is much more   
   affected by base current    
   rather than collector voltage, it is still Re times hfe.    
      
   The Re remains constant through all ranges, but the hfe does not. Since the   
   base is current operated that means that feeding it with a solid (low   
   impedance) voltage source can introduce non-linearity in the output because of   
   variations of hfe within the    
   operating range.    
      
   Tell me if I am wrong with my assertions. I am trying to better understand   
   linear amplification in signals like audio and video, and instrumentation.    
      
   Am I totally wrong, partly wrong or actually right ?    
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)