, The propagation time for this arrangement can be less than a nanosecond, including the signal delay getting on and off the IC package. With two inputs and two outputs, this forms a differential amplifier stage. Based on the methods of providing input and taking output, differential amplifiers can have four different configurations as below. Linear equivalent half-circuits The right figure shows the transfer characteristic of the differential amplifier (REF=40VT/IEE). It is the fundamental building block of analog circuit. This chapter has presented information on differential amplifiers. We can calculate the differential voltage gain as follows. The MECL 10H family was introduced in 1981. In some cases 50 Ω line termination resistors connected between the bases of the input transistors and −2 V act as emitter resistors.. Let's assume that we make the coupling capacitors, C1 and C2, sufficiently large so that we can view them as AC shorts for the signal frequencies of interest. Linear ic applications: UNIT-1 DIFFERENTIAL AMPLIFIER: A differential amplifier is a type of that amplifies the difference between two input but suppresses any voltage common to the two inputs. Figure 12.2.1: A long-tailed pair with resistor loads. The dc collector voltage of the first stage given as base bias voltage to the second stage circuitry. The differential amplifier is probably the most widely used circuit building block in analog integrated circuits, principally op amps. It would be advantageous if our differential amplifier had more symmetric inputs where the input impedance for both the positive and negative inputs was as high as possible, ideally infinite. Consequently, two complementary versions were used: an NPN version and a PNP version. There are numerous differential amplifier applications in practical circuits, signal amplification applications, controlling of motors & servo motors, input stage emitter-coupled logic, switch, and so on are common applications of the differential amplifier circuit. The circuit is insensitive to the input voltage variations and the transistor stays firmly in active linear region. The resistor R L is used as a load impedance. Consider the single transistor amplifier stage, figure 12.1.1, which is similar to what we explored in the section on the degenerated common emitter back in Chapter 9. This is a common emitter amplifier with R E . The inverting or negative input terminal of our simple difference amplifier has the relatively high input impedance of the common emitter stage while the non-inverting or positive input terminal of the amplifier has the relatively low input impedance of the common base stage. ECL's major disadvantage is that each gate continuously draws current, which means that it requires (and dissipates) significantly more power than those of other logic families, especially when quiescent. Single Input Balanced Output 3. Some type of ECL has always been the fastest logic family.  The MIPS R6000 computers also used ECL. As the constant voltage drops across the collector resistors change slightly (or not at all), the output voltages follow the supply voltage variations and the two circuit parts act as constant current level shifters. If we instead DC couple the now symmetric inputs the biasing resistors become unnecessary and our difference amplifier now takes on the look of the classic differential pair we will discuss in the next section. Section, Sedra; Smith. Yourke. Differential Amplifier is an important building block in analog integrated circuits. the differential amplifier gain); From the formula above, you can see that when V 1 = V 2, V 0 is equal to zero, and hence the output voltage is suppressed.  ECLinPS has 500 ps single-gate delay and 1.1 GHz flip-flop toggle frequency. Half-circuit incremental analysis techniques. Beginning in the early 1960s, ECL circuits were implemented on monolithic integrated circuits and consisted of a differential-amplifier input stage to perform logic and followed by an emitter-follower stage to drive outputs and shift the output voltages so they will be compatible with the inputs. , ECL was invented in August 1956 at IBM by Hannon S. Dual Input Unbalanced Output 4.  In addition, the essentially constant current draw of the differential amplifiers minimises delays and glitches due to supply-line inductance and capacitance, and the complementary outputs decrease the propagation time of the whole circuit by reducing inverter count. As a result, its input voltage does not affect the output voltage.