AP 3302 Pt. 3
Section 2
CHAPTER 2
Square Waves applied to CR circuits
The time constant CR = 0.001 x 10-6 x 2 x 106 = 2,000 us.
This is more than ten times the pulse duration so that the combination is a long CR to this particular input.
The resultant steady-state waveforms of VC and VR are shown in Fig lOb and are derived in much the same way as that for a medium CR circuit. The mean value of VC rises and that of VR falls until eventually the mean value of VC is + 50V and that of VR is zero volts. In this case however, since we have a long CR, the building-up process takes longer and the final swings of VC about + 50V are much smaller.
The waveform of VR is a slightly distorted square wave, almost identical with the input except for the change of mean level. The longer CR is made, the less distorted is VR. Thus for a square wave to be passed by a CR circuit without distortion a long CR must be used and the output must be taken across the resistor (Fig 11).
Integrating Circuit
Some radar circuits use triangular waveforms. One method of obtaining them is to apply a symmetrical square wave to a long CR circuit and take the output across the capacitor. A CR circuit used for this purpose is called an integrating circuit (Fig 12).
