







       
  
Circuits and descriptions above op. and comparators


     


This circuit uses an LM139 (LM339) to form a noninverting comparator with hysteresis. This can be used to suppress oscillations and can make the comparator act like a Schmitt trigger.


      
This circuit uses a LM107 to form a simple low pass filter. This circuit has a 6dB per octave rolloff after a closed loop 3 dB point defined by fc. Gain below this corner frequency is defined by the ratio of R3 to R1. The circuit may be considered as an AC integrator at frequencies well above fc; however the time domain response is that of a single RC rather than an integral. The zero dB (gain) point is defined by fL. R2 should be chosen equal to the parallel combination of R1 and R3 to minimize errors due to bias current. The amplifier should be compensated for unitygain or an internally compensated amplifier can be used.



 
This circuit uses a CLC400 op amp to form an adjustable bandwidth amplifier. By increasing the inverting input impedance (which is normally very low) of a current feedback op amp, the bandwidth of the op amp can be reduced. The bandwidth of the circuit shown can be varied over a range of 60MHz to 160MHz.



   
This circuit uses an LM107 op amp to form a difference amplifier. The difference amplifier is the compliment of the summing amplifier and allows the subtraction of two voltages or, as a special case, the cancellation of a signal common to the two inputs. Circuit bandwidth may be calculated in the same manner as for the inverting amplifier, but the input impedance is somewhat more complicated. Input impedance for the two inputs is not necessarily equal; inverting input impedance is the same as for the inverting amplifier and the noninverting input impedance is the sum of R3 and R4. Gain for either input is the ratio of R1 to R2 for the special case of a differential input singleended output where R1=R3 and R2=R4.


    
