In order to aid in the implementation and evaluation of analog active filters, we will now develop the code necessary for the calculation of component values and the generation of PSpice text files. These text files will serve as input to PSpice that will analyze the active filters.

We will use two structures to pass information to the various functions in this project. The first structure is the familiar Filt_Params structure, discussed previously. The second is a new structure used to hold the component values for the active filters to be designed. This RC_Comps structure is shown below and includes the voltage divider resistors R _x and R _y as well as the number of stages in the filter. The other variables contained in the structure are pointers to arrays because these variables will be present in each stage of the filter and we will not know at the time of the program execution how many stages will be present. The components included are the primary R and C values, the gain control resistors R _A and R _B, and the bandstop parameters R _o and C _o.

typedef struct{ double  Rx,Ry,    /*  Voltage divider values */          *R,*C,    /*  Primary R-C values */          *Ra,*Rb,  /*  Feedback resistors */   ...