3-36
(TC = RC). To determine the number of time constants (or the fraction of 1TC) used, divide the time for 1
time constant into the time that the capacitor is allowed to charge:
In figure 3-41, view (B), gate length is 500 microseconds and TC is the product of R2 (5 kilohms)
and C2 (1 microfarad). The number of time constants is computed as follows:
Therefore, 0.1TC is the length of time required to produce a linear rise in the sawtooth waveform.
shows that an increase in gate length increases the number of time constants. An increase in the number
of time constants decreases linearity. The reason is that C2 now charges to a greater percentage of the
applied voltage, and a portion of the charge curve is being used that is less linear. The waveform in figure
3-42, view (A), shows an increase in amplitude (physical length), an increase in the time that C2 is
allowed to charge (electrical length), and a decrease in linearity. If a smaller percentage of VCC is used,
the gate length is decreased. As shown in view (B), this decreased gate length results in an increase in
linearity, a decrease in the time that C2 is allowed to charge (electrical length), and a decrease in
amplitude (physical length).
