# Ratioed Logic Circuits Inverter

Apart from the complementary CMOS inverter, there are other forms of MOS inverters that can be used to build logic gates. Figure 1(a): shows a generic nMOS inverter that uses either a resistive load or a constant current source.

For the resistor case, if we superimpose the resistor load line on the I-V characteristics of the pull-down transistor (Figure 1(b)), we can see that at o the output is some small V (Vo) Figure 1(c) e when v,-o, vo. rises to Voo. As the resistor is made larger, the Vo decreases, and the current flowing when the inverter is turned on decreases.

Correspondingly, as the load r resistor is decreased in value, the να rises and the ON current: rises. Selection of the resistor value would seek a compromise between Vo the current drawn, and the pull-up delay that r increases with the value of the load resistor. Current sources all have high output resistance and thus offer sharper transitions.

Neither high-value resistors nor ideal current sources are readily available in most CMOS processes. A more practical circuit called a pseudo-nMOS inverter is shown in figure 2 (a). It uses a pMOS transistor pull-up or load that has its gate permanently grounded to approximate a constant of the current source. Pseudo-nMOS circuits get their name from an early nMOS technology (which preceded CMOS technology as a major systems technology) in which only ut nMOS transistors were available; the grounded pMOS R transistor is reminiscent of a depletion mode nMOS transistor that is always ON.

The transfer characteristics may again be derived by finding Vo for which L for a given Vi, as shown in Q Figure 2 (b) and Figure 2 (c). The beta ratio affects the shape of the transfer characteristics and the Vou of the inverter Larger pMOS transistors offer faster rise times but less sharp transfer characteristics. Figure 2 (d) shows that when the nMOS transistor is turned on, a constant DC current flows in the circuit.

The gates in this section are called ratioed circuits one is because the transfer function depends on the ratio of the opposing strength of the pull-down transistor to the pull-up device. The net resistor, current source, or ON transistor is sometimes called a static load. It is possible to construct other radioed circuits such as NAND or NOR gates by replacing the pull-up transistors with a single pull-up device.
s to dissipate power continually in certain states (e.g. when the output is low) and have poorer noise margins than complementary circuits.

Therefore, ratioed circuits tend to be used only in very limited circumstances where they offer critical benefits such as smaller areas or reduced input capacitance.

### Limitations of Terzaghi Theory

Limitations of Terzaghi Theory The value of the coefficient of consolidation has been assumed to be constant.  The distance d of the drainage path cannot be measured accurately in the field. The thickness of the deposit is generally variable, and an average value has to be estimated.  There is sometimes difficulty 1n locating the drainage face, sometimes thin previous seams that can act as good drainage face are missed in the boring operations. The equation is based on the assumption that the consolidation is one-dimensional. In the field, the consolidation is generally 3-dimensional. The lateral drainage may have a significant effect on the time rate of consolidation. The initial consolidation and secondary consolidation have been neglected. Sometimes these form an important part of the total consolidation. In actual practice, the pressure distribution may be far from linear or uniform. Read More Muller-Breslau principle

### Price Guard Wire Method

Price Guard Wire Method Some form of  Price Guard Wire Method  is generally used to eliminate the errors caused by leakage currents over insulation. Fig. 3.14 illustrates the operation of This Method. In fig 3.14(a), a high resistance mounted on a piece of insulating material is measured by the ammeter voltmeter method. The micro-ammeter measures the sum of the current through the resistor (IR) and the current through the leakage path around the resistor. The measured value of resistance computed from the readings indicated on the voltmeter and the microammeter, will not be a true value but will be in error.   Figure 3.14 Application of  guard  circuit for measurement of high resistance In fig, 3.14 (b), the  guard  terminal has been added to the resistance terminal block. The  guard  terminal surrounds the resistance terminal entirely and is connected to the battery side of the micro-ammeter. The leakage current IL now

### Streamer Theory of Breakdown in Gases

Streamer Theory of Breakdown in Gases According to the Townsend theory firstly, current growth occurs as a result of the ionization process only. But in practice, breakdown voltages were found to depend on the gas pressure and the geometry of the gap. Second chances time lags of the order of 10-5 s, but practically it was observed to occur at a very short time of 10-8 s. Also, the Townsend mechanism predicts a very diffused form of discharge, that actually discharges were found to be filamentary and irregular. Townsend's mechanism failed to explain all these observed phenomena and as a result, The Streamer theory was proposed. The theory predicts the development of a spark discharge directly from a single avalanche in which the space charge developed by the avalanche itself is said to transform the avalanche into a plasma steamer. In Fig 1.7, a single electron starting at the cathode by ionization builds up an avalanche that crosses the gap. The electrons in the a