BICMOS AND STEERING LOGIC PDF

Characteristics of Logic Families Speed The speed of a logic circuit is the time between which a single is applied at the input, and an output is received. Fan-In Fan-in determines the maximum number of inputs a logic gate can handle. A 2-input AND gate has a fan-in of 2. An inverter has a fan-in of 1. Fan-Out Fan-out determines the number of circuits that a gate can drive, i.

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Mohamed M. Texas Instruments introduced the series TTL family in Transistor—transistor logic uses bipolar transistors to form its integrated circuits. Since the transistors of a standard TTL gate are saturated switches, minority carrier storage time in each junction limits the switching speed of the device. Variations on the basic TTL design are intended to reduce these effects and improve speed, power consumption, or both.

The German physicist Walter H. Schottky formulated a theory predicting the Schottky effect , which led to the Schottky diode and later Schottky transistors. For the same power dissipation, Schottky transistors have a faster switching speed than conventional transistors because the Schottky diode prevents the transistor from saturating and storing charge; see Baker clamp.

Gates built with Schottky transistors use more power than normal TTL and switch faster. Since the initial devices used oxide-isolated metal gates, they were called CMOS complementary metal—oxide—semiconductor logic. A CMOS gate draws no current other than leakage when in a steady 1 or 0 state. When the gate switches states, current is drawn from the power supply to charge the capacitance at the output of the gate. This means that the current draw of CMOS devices increases with switching rate controlled by clock speed, typically.

However, because the logic thresholds of CMOS were proportional to the power supply voltage, CMOS devices were well-adapted to battery-operated systems with simple power supplies. CMOS gates can also tolerate much wider voltage ranges than TTL gates because the logic thresholds are approximately proportional to power supply voltage, and not the fixed levels required by bipolar circuits.

The required silicon area for implementing such digital CMOS functions has rapidly shrunk. The extremely small capacitance of the on-chip wiring caused an increase in performance by several orders of magnitude. Reduced energy implies less heat dissipation. By lowering the power supply from 5V to 3. Many motherboards have a voltage regulator module to provide the even lower power supply voltages required by many CPUs. It was known as the 74HC which used anywhere from 3. The CMOS—TTL logic level problem[ edit ] Interconnecting any two logic families often required special techniques such as additional pull-up resistors , or purpose-built interface circuits, since the logic families may use different voltage levels to represent 1 and 0 states, and may have other interface requirements only met within the logic family.

These devices only work with a 5V power supply. These are generally used "on-chip" and are not delivered as building-block medium-scale or small-scale integrated circuits. Improved versions[ edit ] With HC and HCT logic and LS-TTL logic competing in the market it became clear that further improvements were needed to create the ideal logic device that combined high speed, with low power dissipation and compatibility with older logic families.

A whole range of newer families has emerged that use CMOS technology.

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Difference between TTL, CMOS, ECL and BiCMOS Logic Families

Further more, this integration of RF and analog mixed-signal circuits into high-performance digital signal-processing DSP systems must be done with minimum cost overhead to be commercially viable. While some analog and RF designs have been attempted in mainstream digital-only complimentary metal-oxide semiconductor CMOS technologies, almost all designs that require stringent RF performance use bipolar or semiconductor technology. RF chip depends on the cost of making the silicon with the required elements; in practice, it must approximate the cost of the CMOS wafer, Cycle times for processing the wafer should not significantly exceed cycle times for a digital CMOS wafer. Yields of the SOC chip must be similar to those of a multi-chip implementation. Much of this article will examine process techniques that achieve the objectives of low cost, rapid cycle time, and solid yield.

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LOGIC FAMILY – Study Material

Additionally, a differential, logic commutation signal is not required. These circuits respond to differential inputs, that is, to the difference between two input signals. In the case where the control signal is inherently single-ended, such as with CMOS logic signals, additional circuitry is used to generate a complementary signal or to generate a reference level which must be applied to the second input of the differential pair. This increases the circuit complexity and power dissipation. There is therefore a need for a current steering circuit which responds to a single-ended input signal without the need to generate a complementary signal or reference level.

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BiCMOS Technology

Mohamed M. Texas Instruments introduced the series TTL family in Transistor—transistor logic uses bipolar transistors to form its integrated circuits. Since the transistors of a standard TTL gate are saturated switches, minority carrier storage time in each junction limits the switching speed of the device. Variations on the basic TTL design are intended to reduce these effects and improve speed, power consumption, or both.

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