Bessel-Thompson Delay Low Pass Filter

The primary purpose of this filter is to add a delay to a pulse or data sequence. The use of the RC time constant allows this delay to be added to both the rising and the falling edge of the pulse. The ideal response 

A Bessel-Thompson filter was designed to have a delay close to 500 /us. The design procedure followed gave exact values for all of the capacitors and resistors. These values are rounded to the nearest value of capacitor available. The SPICE packages are used to determine what the implemented delay will be. Measured values of all the components used in the hardware are used. The schematic and the breadboard results are shown as Figs. 3.23 and 3.24, respectively. 

IsSpice had an LM124 model in its library. The simulation response to a step input is shown in Fig. 3.25, and the AC simulation results are shown in Fig. 3.26. 

PSpice has a model for LM324, but the the UA741 op-amp model was used in its place. The operation amplifier does not play a critical role in this circuit because of its slow response. The limiting parameter of the delay time is the RC time constant and not the slew rate or drive capability of the operational amplifier. The PSpice model response to a step input is shown in Fig. 3.27, and the AC results are shown in Fig. 3.28. 

Micro-Cap also had an LM124 model. The model response to a step input is shown as Fig. 3.29, and the AC results are shown as Fig. 3.30. 

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Bessel-Thompson Delay Low Pass Filter with Pulse Shaper... 

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