JPH0241867Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an integrated circuit having an emitter follower output circuit.

Demand for ECL integrated circuits, which are capable of operating at the highest speed among integrated circuits, is expanding in equipment that is becoming increasingly complex and sophisticated. As shown in Figure 1, the basic circuit of the ECL type integrated circuit is a current switching circuit consisting of transistors 2, 3, and 4, each emitter connected to a constant current power source 1, and resistors 6 and 7 connected to the collector. Emitter follower transistor 5 at the output of the circuit
, and its emitter is applied to an external load via an external connection terminal 8 of the integrated circuit.
At this time, even if the external load is a capacitive load, the low driving impedance of the emitter follower transistor 5 allows charging to be performed at high speed, so that extremely high-speed switching is possible. Furthermore, a so-called wired OR connection in which a logic operation is performed by simply connecting the emitters of a plurality of emitter follower output circuits in common is also possible, which is effective in reducing the number of logic stages.

Conventionally, ECL type integrated circuits with these features were
The emitter of the transistor 5, which is the emitter follower output circuit, is directly connected to the external connection terminal 8.
It is led out of the chip without being terminated with a resistor. As the terminating resistor, an individual resistor having a resistance value matching the impedance of the signal propagation line connected to the external connection terminal 8 was generally connected outside the integrated circuit. However, this configuration has the disadvantage that when the number of emitter follower output circuits increases, a large number of individual resistors are required, and the number of external elements cannot be reduced.

To solve this problem, it has been experimentally considered to connect a termination resistor to the emitter of the emitter follower transistor 5 on the integrated circuit chip, but in this case, the signal input section of the circuit that receives the output signal is Since the signal source impedance becomes high impedance due to the impedance of the signal propagation line, if the signal propagation line becomes somewhat long, signal reflection occurs, making high-speed operation impossible. In addition, when using an emitter follower output circuit in which termination resistors are connected on an integrated circuit chip, when implementing the wired OR connection described above, the termination resistors are connected in parallel by the number of emitter follower output circuits to be wired OR connected. As a result, the termination impedance was too low, making wired OR connection practically impossible unless the output drive capability of the emitter follower output circuit was greatly increased.

The present invention eliminates these drawbacks and provides an integrated circuit having an emitter follower output circuit that has a high integration density, enables wired OR connection, and realizes a termination method that allows complete termination.

According to the present invention, a terminating resistor is prepared in the integrated circuit chip separately from the emitter follower output circuit, one end of the terminating resistor is connected to one of the power supply terminals, the other is connected to an external connection terminal of the chip, and the other end is connected to one of the power supply terminals. An integrated circuit having a configuration that is electrically independent from the circuit elements of is obtained.
Since the terminating resistor is provided within the integrated circuit chip, there is no need to prepare and use a separate terminating resistor externally, thereby increasing packaging density. Furthermore, even when multiple emitter follower output circuits are wired OR connected, an appropriate termination resistor can be selected and connected, so the termination impedance will not drop too much.

Next, the present invention will be explained with reference to the drawings.

FIG. 2 schematically shows an embodiment of the present invention, in which circuit elements formed on an integrated circuit chip 10 are shown by circuit symbols. The base of the transistor 21 is connected to the input terminal 13 for external connection. The emitters of the transistors 21 and 22 are commonly connected to the constant current source 16, and the collectors of the transistors 21 and 22 are connected to load resistors 31 and 32, respectively.
The collector of transistor 22 is transistor 23
connected to the base of. The emitters of the transistors 23 and 24 are also commonly connected to the constant current source 17, and their collectors are also each connected to a load resistor 3.
3 and 34 are connected. The collector of the transistor 24 is connected to the emitter follower transistor 25, and its emitter is connected to the output terminal 14 for external connection.
connected only to Transistor 26 constitutes another circuit. Terminating resistors 35 and 36 exist independently on integrated circuit chip 10, and one end of each of these terminating resistors 35 and 36 is connected to power supply (V _EE ) terminal 15 through wiring. Further, the other end of the terminating resistor 35 is connected to the external connection terminal 12, and the other end of the terminating resistor 36 is connected to another external connection terminal 11.

If the emitter follower output circuit formed by the emitter follower transistor 25 needs to be terminated with a terminating resistor, the terminating resistor (the terminating resistor 35 in FIG. , 36) is terminated with an impedance that matches the signal propagation line immediately before the circuit that receives the signal. By doing so, reflection can be eliminated due to electrical characteristics. In this embodiment, when receiving a signal from the emitter follower output circuit at the external connection input terminal 13, the external connection input terminal 13 and the external connection terminal 11 or 12 may be directly connected. In addition, the outputs of a plurality of emitter follower output circuits are wired OR-connected to the input terminal 13 for external connection.
Similarly, when receiving external connection input terminal 13,
This can be easily realized by directly connecting the external connection terminal 11 or 12 and connecting the terminating resistor 35 or 36.

Compared to the conventional configuration in which a terminating resistor is connected to the output part of an emitter follower output circuit composed of emitter follower transistors, in the present invention, the emitter follower output circuit is provided with terminating resistors 35 and 36 in advance on the integrated circuit chip 10. is not connected,
Since a terminating resistor is connected on the signal receiving side connected to the emitter follower output circuit, there is no possibility that the impedance of the signal propagation line increases the signal source impedance seen from the receiving circuit and causes electrical reflection. Further, even if a plurality of emitter follower output circuits are wired OR-connected, the terminating resistors are not connected in parallel, and therefore the resistance value of the terminating resistor can be set to an appropriate value. If there are multiple receiving circuits for the output of the Emitsuta follower output circuit,
This can be achieved by using a termination resistor provided in the integrated circuit containing the receiving circuit at the farthest end.

As is clear from the above explanation, according to the present invention, it is possible to provide an integrated circuit having an emitter follower output circuit that has a high packaging density, enables wired-OR connection, and can realize good electrical characteristics, and can be used in practical applications. Its effectiveness is extremely high.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional ECL type integrated circuit.
FIG. 2 is a diagram showing an embodiment of the present invention. 1, 16, 17... constant current source, 10... integrated circuit chip, 2, 3, 4, 5, 21, 22, 23,
24, 25, ...transistor, 6, 7, 31,
32, 33, 34... Resistor, 35, 36... Terminating resistor, 8, 11, 12... External connection terminal, 13
... Input terminal for external connection, 14 ... Output terminal for external connection, 15 ... Power supply terminal.

Claims (1)

[Scope of utility model registration request] The integrated circuit chip includes an emitter follower output circuit consisting of a transistor whose emitter is directly connected to one of the external connection terminals, and a plurality of resistors that are electrically independent from other circuit elements. An integrated circuit characterized in that one terminal of each is connected to one of the power supply terminals, and the other terminal is connected to each one of the other external connection terminals formed on the integrated circuit chip. circuit.