What is the logical effort of a NAND gate?

DEF: Logical effort is the ratio of the input capacitance of a gate to the input capacitance of an inverter delivering the same output current.

How do you calculate logical effort?

The logical effort of a two-input NAND gate is calculated to be g = 4/3 because a NAND gate with input capacitance 4 can drive the same current as the inverter can, with input capacitance 3. Similarly, the logical effort of a two-input NOR gate can be found to be g = 5/3.

What is logical effort of a circuit?

To compute the logical effort Page 5 of an arbitrary logic gate, design a circuit that performs the intended logic function with the same drive characteristics as an inverter. Then the logical effort is the ratio of the input capacitance of one of the logic gate’s inputs to the input capacitance of the inverter.

What is logical effort in VLSI?

The method of logical effort is an easy way to estimate delay in a CMOS circuit. It is founded on a simple model of the delay through a single MOS logic gate. The model describes delays caused by the capacitive load that the logic gate drives and by the topology of the logic gate.

How do you calculate parasitic delay?

Normalised delay d of a gate can be expressed as the sum of parasitic delay p and effort delay f d = p + f . The effort delay depends on the fan-out n of the gate f = g h , here g is a logical effort.

What is f04 delay?

As a delay metric, one FO4 is the delay of an inverter, driven by an inverter 4x smaller than itself, and driving an inverter 4x larger than itself. Both conditions are necessary since input signal rise/fall time affects the delay as well as output loading.

What is inverter delay?

The propagation delay of a logic gate e.g. inverter is the difference in time (calculated at 50% of input-output transition), when output switches, after application of input. The delay is usually calculated at 50% point of input-output switching, as shown in above figure.

What is the parasitic delay?

Parasitic delay of the gate, is the delay when the gate drives zero load. It is comfortable to use the term of normalised parasitic delay, which is the ratio of diffusion capacitance to the gate capacitance of certain process.

How do I find my Elmore delay?

Time constant for the Elmore delay for an RC interconnect can be calculated by the formula (3) τ D i = ∑ i = 1 N R i k C i where is the total number of nodes in the RC equivalent circuit, R i k is the resistance of the portion of the path to the and is the capacitance at node .

Why is fanout 4?

FO4 is generally used as a delay metric because such a load is generally seen in case of tapered buffers driving large loads, and approximately in any logic gate of a logic path sized for minimum delay. Also, for most technologies the optimum fanout for such buffers generally varies from 2.7 to 5.3.

What is fanout CMOS?

Fanout is the number of CMOS logic inputs that can be driven by one CMOS logic output. Therefore, fanout is equal to the output current of the driving IC divided by the input current of the driven ICs: Fanout = IOH / IIH or IOL / IIL.

A NAND gate is shown in Figure 5. Here input capacitance for input A or B is 4 × C i n while the input capacitance for Inverter was 3 × C i n. The logical effort of Inverter is considered to be 1, or consider it to be a reference for all the delay oriented calculations in transistor logic. Hence the logical effort of NAND gate will be 4 / 3.

What is the logical effort of a gate?

DEF: Logical effort is the ratio of the input capacitance of a gate to the input capacitance of an inverter delivering the same output current.

How is the logical effort of an inverter defined?

Logical effort is defined as the ratio of the input capacitance of a gate to the input capacitance of an inverter delivering the same output current. It is defined as the number of times worse it is at delivering output current than would be an inverter with identical input capacitance. Logical effort (g) depends upon following parameters:

How is logical effort used in logic design?

Logic designer often use Logical Effort to arrive at these conclusions. It uses a simple model for delay calculations and helps to make rapid comparisons between alternative structures. As we all know, gates are made up of transistors. The most basic gate is the NOT gate ,famously known as an inverter.