Transient response analysis of E/D MOS inverter

1. Switching time  Same as E/D MOS inverter, the input level is determined by "< /span>0" jumps to "1", or jumps from "1" to "0”, the E/D MOS inverter must pass the load capacitance when it changes from cut-off to on or from on to cut off.Discharge or charge. The turn-on process of the E/D MOS inverter is similar to the case of the dry fall time of the E/E MOS inverter analyzed above, and the value is relatively small, so I will not go into details here. The following mainly discusses the rise time (ie cut-off time) of the side phase device. Transient response of E/D MOS inverter

During the rising process of the output pulse, the input tube is cut off and the load capacitanceCharge through the conductive load tube. In this process, the load tube has gone through two working states, saturated zone and unsaturated zone, as shown in Figure 2-37(b). Now discuss the charging time in the saturated zone and the charging time in the unsaturated zone respectively.

(1) Charging time in saturation area  When When the load tube is working in the saturation zone, since the load tube is depleted, the current in the saturation zone is constant For , it has nothing to do with the output voltage, so it is constant current charging. The charging time in the saturation zone is the voltage across the capacitor from to The required time, use means. The charging current is:

From , you can get the charging time of the load tube in the saturation zone:

(2) Charging time in unsaturated zone, the load tube works in the non-saturated region, which is composed of the current in the non-saturated region and the through capacitance are equal, and the voltage across the capacitor can be obtained from The time to charge to (That is, the charging time of the load tube in the unsaturated zone) is:

So the total rise time t is:

Through the above analysis, we know that the rise time of E/D MOS is related to the size and pinch-off voltage of the load tubeAbout. If you want to be smaller than , then is large, but this contradicts the well-designed DC characteristics. Therefore, in the design, reasonable design parameters must be selected according to the design index.

For the saturated load of E/D MOS, as the output voltage gradually approaches, the load capacitance is The charging current will become smaller and smaller, so the rise time is very long and the circuit speed is slower. The E/DMOS load tube has the characteristics of a constant current source, and the rise time is much shorter, so it can increase the operating speed of the circuit. Transient response of E/D MOS inverter

To sum up, E/DMOS has the three advantages of large output amplitude, strong anti-interference ability and fast speed. However, it is more complicated to fabricate devices with two different channels of depletion mode and enhancement mode on one wafer at the same time.

2. The quality factor of E/DMOS The static power consumption of E/DMOS is:

Speed can be approximated means that because is better than is much smaller. If it is expressed as an approximate formula:

The quality factor can be approximated as:

It can be seen that the higher the power supply voltage, the higher the charging current, it is easier to reach a predetermined high level, so the faster the switching speed, but the power consumption increases significantly. In the design, it should be considered as a whole according to the requirements.

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