![]() ![]() The cookies we use can be categorized as follows: Strictly Necessary Cookies: These are cookies that are required for the operation of or specific functionality offered. When the input is brought low again a similar process occurs in the upper portion of the stack and the snapping action takes place when the lower threshold its reached. The snapping action is due to greater than unity loop gain through the stack caused by positive feedback through the source follower transistors. With M 3 off, V OUT will collapse all the way down to ground. M 5 turning on brings the source of M 3 low and turns M 3 off. Meanwhile M 5 has started to turn on, its gate being brought low by the rapidly dropping V OUT. When V OUT drops, the source of M 6 follows its gate, which is V OUT, the influence of M 6 in the voltage divider with M 2 rapidly diminishes, bringing V OUT down further yet. Any more voltage on the input causes V OUT to drop. When the input is a threshold above 1/2 V DD, M 4 begins to turn on and regenerative switching is about to take over. ![]() If the input voltage is ramped up to one threshold above ground transistor M 2 begins to turn on, M 2 and M 6 both being on form a voltage divider network biasing the source of M4 at roughly half the supply. ![]() Since V OUT is high, M 6 is on and acts as a source follower, the drain of M 2, which is also the source of M 4, is at V DD - V TH. When V IN is at 0V, transistors M 1 and M 3 are on, and M 2, M 4 and M 5 are off. A narrow transition region also potentially reduces the amount of time the output spends transitioning between states and thus the so called “shoot through” current when both the NMOS and PMOS transistors are partially turned on. Given that there is likely to be noise superimposed on the input signal it is desirable to have the output not respond to small changes in the input. The width of the transition region as a fraction of the power supply leads to a performance measure that is often referred to as the noise margin, the part of the input range where the output remains at a constant high or low level. This very fact is the reason that today nearly all digital circuitry is now build using CMOS technology. The fact that there are two parts of the characteristic curves when the input voltage is near ground and V DD, no current flows between V DD and ground, is very attractive because there is no power dissipation at this stages. The supply current characteristic plots the current flowing through the transistors between V DD and ground also versus the input voltage V IN. Notice that when the input voltage increase from 0V to 5V the output voltage decreases from 5V to 0V. The input to output transfer characteristic plots the output voltage V OUT versus the input voltage V IN. Figure 6 Scopy screenshots: Inverter output voltage and supply current curves vs. ![]()
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