4-30 Figure 4-24B.—Common-base configuration clamper. Look at view (B) as we continue. The input signal is a square-wave pulse type signal that varies in amplitude. Without an input signal, Q1 conducts and provides current through R1. This develops the output (collector to ground) potential which is assumed to be approximately -5 volts (V_{CC}-E_{R1}) for this discussion. From T0 to T1 the output follows the input because of the increasing emitter-base forward bias. However, at T1 the collector voltage reaches -2 volts and D2 is forward biased. D2 conducts and limits the output to -2 volts (the value of B3). D2 conducts until T2 when the input decreases below -2 volts. At this time, D2 cuts off and the output again follows the input because of the decreasing forward bias on Q1. At T3 the input reaches -8 volts and forward biases D1. D1 conducts and any further increase (beyond -8 volts) of the input has no effect on the output. When the input returns to a value more positive than -8 volts, D1 cuts off and the output again follows the input. This circuit action is the same for all inputs. The output remains the same as the input except that both positive and negative extremes are clamped at -2 and -8 volts, respectively. SHAPING CIRCUITS Timing circuits and circuits which require a particular shape or "spike" of voltage, may use SHAPING circuits. Shaping circuits can be used to cause wave shapes, such as square waves, sawtooth waves, and trapezoidal waves, to change their shape. Shaping circuits may be either series RC or series RL circuits. The time constant is controlled in respect to the duration of the applied waveform. Notice that the wave shapes mentioned did not include the sine wave. These RC or RL shaping circuits do not change the shape of a pure sine wave. The series RC and RL circuits electrically perform the mathematical operations of INTEGRATIONand DIFFERENTIATION. Therefore, the circuits used to perform these operations are called INTEGRATORS and DIFFERENTIATORS. These names are applied to these circuits even though they do not always completely perform the operations of mathematical integration and differentiation.