Why do we gradually increase the size of inverters in buffer design when trying to drive a high capacitive load?

Why is the size of inverters in buffer design gradually increased? Why not give the output of a circuit to one large inverter? Because circuit can not drive the high output load straight away, so the load is gradually increased, by gradually increasing the size of inverters to get an optimized performance.

Why should the number of CMOS transistors that are connected in series be reduced?

It reduces the count of transistors used to make different logic gates, by eliminating redundant transistors. By contrast, conventional CMOS logic switches transistors so the output connects to one of the power supply rails, so logic voltage levels in a sequential chain do not decrease.

What is the effect of increasing the VDD on the propagation delay?

Increasing VDD above a certain values yields minimal improvement to delay. Reliability issues – oxide breakdown, hot carrier effects.

How the transfer characteristic of a CMOS NAND gate is affected with increase in fan in?

Q1. How the transfer characteristic of a CMOS NAND gate is affected with increase in fan-in? Ans: Transfer characteristic does not remain symmetric with increase in fan-in of the NAND gate. The inversion voltage moves towards right with the increase in fan-in.

What is the importance of gain in inverter circuit?

The gain of the inverter actually increases with a reduction of VDD . At a VDD =0.5V, which is just 100mV above VT of the transistors. So why can’t we operate all digital circuits at low VDD values? Yes, you get lower power consumption.

How can power dissipation of a CMOS inverter can be decreased?

Power is always dissipated in CMOS circuit when there is switching at the output node. You can always reduce the power by reducing the operating frequency but due to continuous demand of increasing the speed of data rate in digital systems this method will not give the useful results.

Does a CMOS inverter have a load as capacitance?

Not only CMOS Inveters but any CMOS for that matter have load as capacitance because CMOS consisting of NMOS and PMOS are MOSFETs which are Field Effect Transistors – Gate Metal -Oxide- channel/nochannel(susbstrate) forming a input capacitor Cg/Ci which is always connected to output of anyother CMOS acts as load.

What does the output voltage curve of a CMOS circuit represent?

The curve represents the output voltage taken from node 3. You can easily see that the CMOS circuit functions as an inverter by noting that when VIN is five volts, VOUT is zero, and vice versa. Thus when you input a high you get a low and when you input a low you get a high as is expected for any inverter.

What is the output voltage of the inverter at VDD?

  For CMOS inverters, VOH=VDD.   VOL is defined to be the output voltage of the inverter at an input voltage of VOH.   We have just proven that VOL=0. The PMOS device is cut off when the input is at VDD (VSG=0 V).

What is the difference between PMOS and NMOS in transmission gate?

In Transmission Gate, PMOS and NMOS aid each other rather competing with each other. That’s the reason why we need not size them like in CMOS. In CMOS design we have NMOS and PMOS competing which is the reason we try to size them proportional to their mobility.