By Paul M. Brown Jr.

Software particular built-in circuits (ASICs), either analog and electronic, became normal procedure point bulding blocks. ASIC owners have tried to supply instruments that they desire will permit fairly green IC designers (i.e. structures engineers) to layout refined customized built-in circuits. This philosophy has been extra winning in electronic know-how than in analog. considerably extra artwork is concerned with analog layout and much fewer automatic instruments can be found. nearly each analog ASIC seller deals diverse semiconductor applied sciences, software units, documentation (usually missing intimately and never supplying the right kind history and guidelines), and ranging degrees of engineering aid. the result's that many engineers who may perhaps use analog ASICs lack the technical info to take action. they don't seem to be convinced whilst customized analog ICs are low in cost or which seller will most sensible serve their wishes. additionally, many engineers would not have enough analog layout event, specifically with built-in circuits. Consqeuently, many that may benefit from analog ASIC know-how don't use it whereas others have undesirable reports which could have simply been shunned.

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Integrated Circuit Components c 9 -I bb' r b O- kijc b' -ΛΛΛΛτ- Figure 3-10 More complex Ebers-Moll model. Hybrid-7r Model The small-signal "linearized" version of the model, illustrated in Fig­ ure 3-11, is the well-known hybrid-^ model. In this model, the com­ ponents are determined as follows: l"cc' l"ee' Tb'e Ib'c' = (same as for Ebers-Moll) = (same as for Ebers-Moll) = (same as for Ebers-Moll) = kT/qI = kT/qI e ec Cb'e' C cs = (same as for Ebers-Moll) The component r < is used to simulate collector-base leakage I and is frequently assumed to be infinite.

Both the resistor value and associated capacitance will vary with applied bias and signal swing. For base resistors, the voltage coefficient is on the order of ± 0 . 0 1 % / V . This value is much higher for ion-implanted resistors due to their shallow junction depth. , junction area) of the resistor and is usually important only for high-gain, high-frequency amplifiers. Table 3-1 summarizes typical diffused resistor characteristics. Figure 3-6 illustrates a base-diffused resistor and the major para­ sitic elements associated with it in the normal operating mode.

At this point, the component structures have been created and all that remains is to interconnect these components into a useful circuit. The first step in "wiring" the circuit is opening contact windows in the oxide (Figure 2-15) to the areas on the components where contact is desired. A layer of aluminum approximately 1 /im thick is then de­ posited on the wafer (Figure 2-16), connecting all of the contact areas exposed in the previous step. The resistivity of the aluminum intercon­ nection is typically 30 πιΩ/sq.

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