#CMOS INVERTER LOGIC DRIVER#

This voltage now equalsĪdditionally, the transient current flows in a large loop creating an efficient loop antenna. During the switching time the voltage V IC no longer equals the source voltage V S potentially causing signal integrity issues. We often refer to these voltages as a power rail collapse and a ground bounce, respectively.ĭuring the off-switching time (dc condition) inductances act as short circuits and the voltage V IC between the driver-IC power and ground pins equals the source voltage V S.

#CMOS INVERTER LOGIC DRIVER#

When the driver IC switches, the current is drawn from the source resulting in the voltages V P and V G across the power and ground inductances. At higher frequencies we would augment the model with additional partial and parasitic inductances between the ICs and within the ICs themselves (see for more details). This model applies at lower frequencies where the partial inductances of the power and ground traces connecting the ICs themselves can be neglected. This is shown in Figure 7.įigure 7: Current loop area and partial inductances To model the flux-induced effect we will insert inductances along the power and ground traces. For each Vdd applied (from 1 to 4 V), the VTC presents complete logic swing, and the maximum voltage gain is bigger than. Summary of Key Concepts Key features of CMOS inverter: CMOS inverter logic threshold and noise margins engineered through Wn/Ln and Wp/Lp. High Av around the logic threshold Good noise margins. Two primary connections are the two-input NAND gate and the two-input NOR gate. It is, therefore, reasonable to insert the lumped parameters only into the forward and return paths. inverter is idle in any logic state rail-to-rail logic Logic levels are 0 and VDD. The inverter, NAND, and NOR logic building blocks are the backbone of most digital logic families. In any practical circuit the forward and return paths (horizontal lines in Figure 9, are orders of magnitude longer than the length of a path between the power and ground pins (vertical lines in Figure 9. When the loop is electrically small at the frequencies considered we can model these distributed effects as lumped sources or inductances. Both the induced voltage and the inductance are distributed along the loop. We can model this phenomenon by inserting either a voltage source somewhere in the loop, or by inserting an inductance somewhere in the loop. This time-varying current creates a time-varying magnetic flux that crosses the loop area of the circuit inducing a voltage drop along the traces. This current flows from the source to the load along the forward path i.e., the power traces and back to the source through the return path i.e., the ground traces.

When a CMOS gate switches a current transient is drawn from the power distribution system (PDN).

Figure 6: CMOS transistors in a high-speed logic circuit

Cmos inverter logic