From: spamtrap42@jacob21819.net   
      
   On 2012-05-18, Moe Trin  wrote:   
   > ...   
   >   
   > That would be even worse - the standard TTL output stage is called   
   > a totem-pole because it consists of (bottom to top) a common emitter   
   > stage with the output lead off the collector, one or two series diodes   
   > and an emitter follower to the top (usually with a current limiting   
   > resistor in the collector) - the bases of the two output transistors   
   > are driven from a "split-load phase inverter" (stage with one output   
   > off the collector, the other off the emitter).  If you look at the   
   > specs for TTL, the "low" output can sink 10-15 ma and remain below a   
   > half volt, but the "high" output can source less than 1 ma, and   
   > "greater than 3 volts".   The typical CMOS output stage has an N   
   > channel stage on the bottom, and an inverted P channel stage on the   
   > top. Neither stage has lots of horsepower, but the "low" and "high"   
   > output voltages will be much closer to the Vdd and Vss rails.   
      
   CMOS inverters, now that brings back memories:   
      
   A 4000-series CMOS inverter can make a pretty good analog gain   
   stage.  Pop 'tronics had an article about them around 1976.  You   
   use capacitive coupling between stages and a high-value resistor   
   (>=1M) between the inverter's input and output to bias it at   
   around mid-point.  +5V and -5V supplies work well to put the bias   
   point near zero.  If you want more precise gain control, you use   
   a series input resistor to create a virtual ground at the   
   inverter's input.  If the feedback resistor is 10X the series   
   input resistor, the stage will have gain of just under 10X.   
      
   My first self-designed major piece of stereo equipment, circa   
   1977 when I was a college freshman, was an integrated amplifier   
   with solid state input switching, tone controls, and and a   
   separate headphone output circuit.  The first edition used (IIRC)   
   type 4449 as the gain elements for everything except the magnetic   
   phono input circuit and power outputs.  The speaker output stages   
   used what I learned later is called the Watts configuration   
   independently invented at GE some years earlier.  There were   
   three speaker outputs (left, center, and right) to drive the   
   three Altec A-7 cabinets I built during the summer after high   
   school.   
      
   The first generation of the amplifier's phono input stage was a   
   learning experience.  The RIAA curve has a greater gain   
   difference between the ends of the audio spectrum than a single   
   CMOS inverter gain stage can provide.  I figured I could put   
   three inverters in series with a feedback loop around all of   
   them.  The circuit became a very nice oscillator, a ring   
   oscillator I later learned, around 100-200kHz as near as I could   
   figure.  It was a few years later than I learned the details of   
   how such an oscillator works.   
      
   --   
   Robert Riches   
   spamtrap42@jacob21819.net   
   (Yes, that is one of my email addresses.)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)