Category Archive for: FET CIRCUITS AND APPLICATIONS

The CMOS Analog Switch

The CMOS Analog Switch A CMOS analog switch, also called a bilateraL transmission gale, is formed by connecting an NMOS device in parallel with a PMOS device we shall presently  combination acts like two parallel newswires, both of which (‘r,p simultaneous Closed or simultaneously open. Actually, when t e switches are closed, both conduct small positive…

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CMOS CIRCUITS

CMOS Inverters Recall that complementary MOS (CMOS) integrated circuits contain both NMOS and PMOS devices embedded in the same chip (see Figure 7-47). The CMOS design is now widely used in general-purpose digital circuits because it provides faster switching times than either PMOS or NMOS devices alone. It is also used  in special-purpose MSI and…

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CAPACITIVE LOADING OF’ SWITCHING CIRCUITS

The output of a switching circuit, such as a MOSFET inverter, always has a certain amount of capacitance in parallel with it. This capacitance may be inherent in the input of the device that serves as the load for the switching circuit, and it may be stray capacitance associated with conducting paths and terminal connections…

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MOSFETINVERTERS

The MOSFET as a Resistor In Chapter 6 we discussed the fact that it is easier and mere efficient to  a transistor than it is to construct a resistor in an integrated circuit. This is  true in enhancement MOSFET circuits because of the simple structure of  devices. For this reason, MOSFETs are connected so that…

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VMOS AND DMOS AMPLIFIERS

VMOS Amplifiers The results of Example 8-8 show that the voltage gain of a MOSFET amplifier, like that of a JFET amplifier, is generally rather small. Voltage gains of FET amplifiers are small because transconductance values are small, typically 3 to 4 mS. On the other hand, VMOS FETs (Figure 7-48) have comparatively large transconductance…

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SMALL-SIGNAL MOSFET AMPLIFIERS

The most convenient small-signal model for a MOSFET, like that of a let, incorporates the trans conductance of the device. Recall that the characteristics of a depletion-type MOSFET are quite similar to those of a JFET, the only difference being that the depletion MOSFET can be operated in both the depletion and enhancement modes. As…

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THE JFET AS AN ANALOG SWITCH

An analog switch is an electronically controlled device that will either pass or shut elf a cotter~ “varying .Figure 8-24 iIlustr res the concept. By way of contrast, digital switch is one whose output switches between oal possible levels (low or high), such as the BJT inverted we discussed in 4. As illustrated in Figure 8-·24,the…

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cycle

plotted in 26 points over one full cycle (l/1Q4Hz == 0.1 ms). The plot, appearing in Figure 8-14(a), shows that the peak-to-peak output is 0.5972 V – (-0.5965 V) = 1.1937 V. Thus, the voltage gain is -(1.193 V p-p)/(O.2 V p-p) = -5.97, where the minus sign reflects the phase inversion evident in the…

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THE JFET CURRENTSOURCE

BJT constant-current sources were discussed extensively in Chapter 6 (Section 6-H). A JFET can be used to supply constant current to a variable load by connecting its gate directly to its source, as illustrated in Figure 8-21. Here, the resistor UII is regarded as the (variable) load resistance. To be able to supply a current…

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THE COMMON-DRAIN AND COMMON-GATE JFET AMPLIFIERS

Common·Drain Amplifier Figure 8-17 shows a JFET connected as a common-drain amplifier. Note that the drain terminal is connected directly to the supply voltage VOD, so the drain is at ac ground. Since the input and output signals are taken with respect to ground, the drain is common to both, which accounts for the name…

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