Page 170 - Analog and Digital Filter Design

167
Highpass Filters

0.099506. Multiplying this by the frequency scaling factor of 6283 gives
m/lll, = 625.197 radls.

Component values can now be found after substituting capacitor value.
C= 150nF and R= IOkR.

1
R1 = R4 = ~ =757Q (750R is the nearest E24 series preferred valu6)
3lIl~C
1
R2 = R3 = ~ = 150052 (a standard value)
W,,l,PC
R5= 3HPW,rIIPR , = 14,213R (14.3kR is the nearest 1"~ tolerance ~alue)
~
~~,,lll, - ~/lll~
wr = the normalized zero frequency.
R6= 4R

Let the gain at DC be unity, A = I. Let the resistors R = R' = IOkR. High
precision resistors are sometimes necessary to achieve values close to those
calculated.

Gyrator Filters

Gyrators are related to the FDNR circuits described in Chapter 4 and are used
to replace inductors. The gyrator uses two op-amps, four resistors, and a capac-
itor. The gyrator can be smaller than the inductor it replaces, especially if
surface-mount components are used. Other advantages of using a gyrator
instead of an inductor are that using suitable components can reduce tempera-
ture effects and that the component vnlue can be adjusted easily.

The gyrator has the same structure as the FDNR: two op-amps connected to ii
chain of passive elements. The gyrator only has one capacitor, instead of the
two used in the FDNR. All remaining passive components are resistors. The
gyrator has a capacitor in place of the fourth element instead of in place of
the first and third element.

A circuit diagram for the gyrator is given in Figure 5.19.