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Sat Jan 8 18:52:18 EST 2011

Random non-tested circuit: Ladder integrator

Something I was thinking about in another post but doesn't do what I
need.  This is an integrator -- needs an output buffer.  

Might not be so useful.  I guess the capacitor could just as well go
on the output instead of between the two current mirror legs.


        o---------------o  Vcc
        |               |
        \               /
     Q3  >|           |<  Q4
          |--o--------|
         /             \
        /    |          \
        o----o          |
        |               |
       --               |
       \/ D1            |
       --          C1   |
        |       ||      |
        o-------||------o--o V_out
        |       ||      |
        |               |
V1 (+)  /               \    V2 (-)
   o--|/ Q1           Q2 \|--o 
      |\                 /|
        V               V
        |               |
        o-------o-------o
                |
                | I0
                \
                 \|---o  Exp controller 
                 /|
                V
                |
              --o-- GND
               

This is a differential pair Q1,Q2 with a current mirror load Q3,Q4.
The diode D1 is for some extra DC bias fixing one end of the capacitor
C1 (might not be necessary).

The Q1,Q2 collector curents have a ratio I1/I2 = exp(V1-V2 / V_T)
while their sum I1+I2 = I0 is set by the long tail current source.
The difference I1-I2 flows through the capacitor.  





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