JPH052055A - Emitter follower type output circuit - Google Patents

Abstract

PURPOSE:To obtain an emitter follower type output circuit by preventing an output current from being changed, malfunction and oscillation from being generated, and preventing other tests from being affected in testing a semiconductor integrated circuit even if an inside of a chip is terminated as in an emitter follower output circuit using a constant-current source. CONSTITUTION:A title item is provided with an output constant-current source transistor 2 which generates an output current, a transistor 3 for switching mode where it is emitter-coupled to this transistor 2, and an input terminal 4 for switching mode. At the time of test, the transistor 3 for switching mode is turned on and an output constant current source transistor 2 is cut off, thus enabling operation as an output circuit to be stopped and enabling a poor influence to other tests to be excluded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an emitter follower type output circuit, and more particularly to an emitter follower type output circuit having an improved test method.
The present invention relates to a follower type output circuit.

[0002]

2. Description of the Related Art FIG. 4 shows an emitter-follower output circuit using a conventional constant current source. A transistor 51 and a resistor are connected in series between the power source 46 and the power source 48,
The input terminal 41 is connected to the base of the transistor 51. A transistor 55 and a resistor are connected in series between the power source 46 and the power source 48, and a constant voltage source is connected to the base of the transistor 55. Further, the transistor 54 is connected to the power source 48 via a resistor,
A parallel connection body of the transistor 52, the transistor 53 and the resistor is connected between the transistor 54 and the power supply 46. On the other hand, an emitter follower transistor 39 and an output constant current source transistor 40 are connected in series between the power source 47 and the power source 48. An output terminal 42 is connected to the emitter of the emitter follower transistor 39 via a resistor, and a constant voltage source 45 is connected to the base of the output constant current source transistor 40. The base of the transistor 52 is connected to the emitter of the transistor 51, the base of the transistor 53 is connected to the emitter of the transistor 43, and the base of the transistor 39 is connected to the collector of the transistor 53.

In the conventional emitter-follower type output circuit having such a structure, when a semiconductor integrated circuit is tested by an LSI tester, a large output current or excessive current causes a malfunction or induces oscillation. It was likely to adversely affect other tests. EC that terminates at -2V with a resistance of 50Ω from outside the semiconductor integrated circuit chip
In the L output, it is possible to reduce the influence of the output current and the transient current by increasing the termination voltage or connecting and disconnecting the LSI tester pin corresponding to the output terminal. However, in the emitter-follower type output circuit using the constant current source as shown in FIG. 4, the termination is already performed inside the semiconductor integrated circuit chip, and the termination method of the LSI tester pin is changed and the LSI which is the output terminal is changed. The output moves between high level and low level regardless of whether the tester pin is connected or disconnected, and the output current constantly changes, which causes malfunction or oscillation due to the effect of excessive current, and cannot adversely affect other tests. It has become a thing.

[0004]

As described above, in the conventional emitter-follower type output circuit, when a semiconductor integrated circuit is tested by the LSI tester, the ECL is used at the -2V termination with a resistance of 50Ω from the outside of the chip. As in the case of the output circuit, there is a problem that it is not possible to take measures to reduce the output current and the transient current by changing the termination voltage and releasing the LSI tester pin, and to eliminate the influence on other tests.

The present invention has been made in view of the above problems, and it is possible to reduce the output current to 0 even in a circuit terminated inside the chip, which causes malfunctions and oscillations due to changes in the output current. It is an object of the present invention to provide an emitter-follower type output circuit capable of preventing adverse effects on other tests.

[0006]

Means for Solving the Problems The emitter according to the present invention
The follower type output circuit is an emitter-follower type output circuit using a constant current source, an emitter follower transistor, an output constant current source transistor, and a mode switching transistor emitter-coupled to the output constant current source transistor. It has a mode switching input terminal to which a signal for switching on / off of the mode switching transistor is input.

[0007]

In the present invention, during the test, a signal is input to the mode switching input terminal to turn on the mode switching transistor. As a result, the output constant current source transistor is cut off, the output current becomes 0, and the operation of the emitter-follower type output circuit is stopped.

[0008]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an emitter-follower output circuit according to an embodiment of the present invention. In FIG. 1, FIG.
The same parts as those in FIG. However, reference numeral 5 is an input terminal, 6 is an output terminal, 10, 1
Reference numerals 1 and 12 are power supplies and reference numerals 7, 8 and 9 are constant voltage sources. In this embodiment, the emitter / follower transistor 1, the output constant current source transistor, and the resistor are the power source 11 and the power source 1.
2 and 2 are connected in series.

A mode switching transistor 3 is connected in parallel to the transistors 1 and 2, and a transistor 60 is provided between the base of the transistor 3 and the power supply 10.
And the diode 61 are connected in series. The mode switching input terminal 4 is connected to the base of the transistor 60.

In the emitter-follower type output circuit configured as described above, when a low level is input to the mode switching input terminal 4, the mode switching transistor 3 is cut off, and the conventional emitter shown in FIG. -Operates as the same output circuit as the follower output circuit. on the other hand,
When a high level is applied to the mode switching input terminal 4,
The mode switching transistor 3 is turned on, the output constant current source transistor 2 is cut off, and the output circuit does not operate.

FIG. 2 shows an example in which a semiconductor integrated circuit is actually tested using the circuit of FIG. The semiconductor integrated circuit chip 13 is equipped with an internal termination type output circuit 15 and a normal open emitter output circuit 16 shown in FIG. The input terminal 17 of each output circuit 15 corresponds to the input terminal 5, and the mode switching input terminal 18 corresponds to the mode switching input terminal 4. Further, the chip 13 is provided with the output terminal 19 of the internal termination type output circuit 15 and the output terminal 20 of the normal open emitter output circuit 16. On the other hand, 1
4 is an LSI tester, 21 is an LSI tester pin, 22
Indicates a terminating resistance.

Therefore, the mode switching input terminal 4 of the circuit of FIG. 1 is grouped into one signal line and controlled by one mode switching terminal 18. The normal operation of the open emitter output circuit 16 can be stopped by disconnecting the LSI tester pin 21 from the output terminal 20.

On the other hand, regarding the internal termination output circuit 15 corresponding to the circuit of FIG. 1, when a high level signal is applied to the mode switching input terminal 18, the output circuit 15 stops its operation and eliminates adverse effects on other tests. It is possible.

That is, in the circuit of FIG. 1, when a low level is applied to the mode switching input terminal 4 (mode switching input terminal 18 of FIG. 2), the mode switching transistor 3 is cut off, and this circuit is conventional. It operates as the same output circuit as in FIG. 4 of the example. When the semiconductor integrated circuit is tested in this state, the output circuit operates regardless of the connection state of the tester pin 21 of the LSI tester 14 to the output terminal 6. However, when a high level is applied to the mode switching input terminal 4, the mode switching transistor 3 is turned on, the output constant current source transistor 2 is cut off, and the output circuit does not operate. Therefore, when a semiconductor integrated circuit is tested, that is, when this output circuit is unnecessary, a high level is applied to the input terminal 4 (input terminal 18) to make the output circuit inoperative, and other tests and surroundings are performed. Can be eliminated. FIG. 3 shows the second aspect of the present invention.
Is an example of. Reference numeral 23 is an emitter follower transistor, 24 is an output constant current source transistor, 25 is a mode switching transistor, 26 is a mode switching input terminal,
27 is an input terminal of the output circuit, 28 is an input / output bidirectional terminal,
29 to 31, 37 to 38 are constant voltage sources, 32 to 34 are power sources, 35 is an input transistor of the input circuit, and 36 is an output terminal of the input circuit.

In this embodiment, the connection of the collector of the mode switching transistor 3 shown in FIG. 1 is changed from the power supply 11 to the base of the emitter follower transistor 1. That is, in FIG. 3, the collector of the mode switching transistor 25 is connected to the base of the emitter follower transistor 23.

As described above, by combining with the input circuit, it is possible to form an input / output bidirectional circuit.
Further, the mode switching input terminal 26 has an advantage that it can perform both the switching of the input / output circuit and the mode switching during the test of the first embodiment.

[0018]

As described above, the present invention can be applied to an emitter follower type output circuit terminated inside the chip.
The output current can be set to 0, and during the test, there is an effect that it is possible to prevent adverse effects on other tests due to malfunction and oscillation due to a change in the output current.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an emitter follower output circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a method of testing a semiconductor integrated circuit using the circuit of FIG.

FIG. 3 is a circuit diagram showing an input / output circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional emitter-follower output circuit.

[Explanation of symbols]

 1; Transistor for emitter / follower 2; Transistor for output constant current source 3; Mode switching transistor 4; Mode switching input terminal 5; Input terminal 6; Output terminal 7-9; Constant voltage source 10-12; Power supply 13; Semiconductor integrated Circuit chip 14; LSI tester 15; Internal termination type output circuit 16; Normal open emitter output circuit 17; Output circuit input terminal 18; Mode switching input terminal 19; Internal termination type output circuit output terminal 20; Normal open emitter Output circuit output terminal 21; LSI tester pin 22; terminating resistor 23; emitter follower transistor 24; output constant current source transistor 25; mode switching transistor 26; mode switching input terminal 27; output circuit input terminal 28; both input and output Terminals 29 to 31, 37 to 38; constant voltage source 32 -34; power supply 35; input transistor of input circuit 36; output terminal 39 of input circuit; transistor for emitter follower 40; output constant current source transistor 41; input terminal 42; output terminal 43 to 45; constant voltage source 46 to 48; Power supply

Claims (1)

Claim: What is claimed is: 1. An emitter follower type output circuit using a constant current source, an emitter follower transistor, an output constant current source transistor, and a mode in which an emitter is coupled to the output constant current source transistor. An emitter-follower type output circuit comprising a switching transistor and a mode switching input terminal to which a signal for switching on / off of the mode switching transistor is input.