JPS63157520A - Signal switching circuit - Google Patents

Abstract

PURPOSE:To miniaturize the titled circuit by applying different DC signals to bases of transistors in which each emitter is connected to a common external connecting terminal, and selecting the signal in accordance with the presence of a bias to be applied to the external connecting terminal from the outside. CONSTITUTION:To bases of transistors TR Q11, Q12 in which each emitter is connected to a common external connecting terminal 18, signals of different DC levels are supplied from input terminals 19, 20. The TRs Q11, Q12 are brought to a complementary connection and form an integrated circuit 17. A collector of the TR Q12 is connected to a DC power source Vcc, and a collector of the TR Q11 is grounded. Also, emitter common connecting points of the TRs Q11, Q12 are grounded through a resistance R11. The external connecting terminal 18 is connected to the power source Vcc through a switch 22 and a resistance R12. In such a state, when the switch 22 is turned off, the TR Q12 is turned on, the TR Q11 is turned off, the signal from the terminal 20 is outputted, and when the switch 22 is turned on, the TR Q12 is turned off, the TR Q11 is turned on, and the signal from the terminal 19 is outputted. In such a way, a simple and miniature switching circuit is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement in a signal switching circuit suitable for use in an integrated circuit such as a television receiver.

(Prior Art) As is well known, when a signal switching circuit used in a television receiver or the like is formed in an integrated circuit,
It is configured as shown in the fifth factor.

That is, by turning off the switch 13 connected to the external connection terminal 12 of the integrated circuit 11, the transistors Q2, Q5, and QB become inactive.

At this time, transistor Q1 operates as a constant current source, so transistor Q3. Q4 becomes active.

Therefore, the first signal supplied to the input terminal 14 is taken out from the external connection terminal 15 of the integrated circuit 11 via the transistor Q7.

On the other hand, when the switch 13 is turned on, the transistors Q5 and Q6 become active, and the second signal supplied to the input terminal 16 is transferred to the external connection terminal 15.
taken from.

That is, depending on the off/on state of the switch 13, the first and second signals supplied to the input terminal 14.16 are
It can be selectively taken out from the external connection terminal 15.

(Problems to be Solved by the Invention) However, in the conventional integrated circuit signal switching circuit as described above, two external connection terminals 12 and 15 are required, and the structure is complicated due to the large number of elements used. The problem is that

Further, in recent years, integrated circuits for television receivers have become highly functional and highly integrated, and there is a need to reduce the number of elements used and the number of external connection terminals (bins). And because it is highly integrated and the number of external connection terminals is reduced,
Another problem has arisen in that it has become difficult to test the quality of integrated circuits.

Therefore, this invention was made in consideration of the above circumstances, and can reduce the number of elements used and the number of external connection terminals to achieve miniaturization, and can also contribute to facilitating pass/fail tests within integrated circuits. The purpose is to provide an extremely good signal switching circuit.

[Structure of the Invention] (Means for Solving the Problems) That is, in the signal switching circuit according to the present invention, each emitter is commonly connected to an external connection terminal, and each base has a first A pair of complementary connected transistors each supplied with a second signal are integrated into an integrated circuit.
and the second signal are selectively obtained.

(Function) According to the above configuration, the elements used in the integrated circuit are only a pair of transistors, and only one external connection terminal is required, so the number of elements used and the number of external connection terminals can be reduced. can be reduced and downsized. In addition, by using the first and second signals supplied to the bases of the pair of transistors as signals to be measured that are processed and generated by a circuit formed within the integrated circuit, necessary signals can be selectively transmitted. It can be taken out and measured, making it easy to perform quality tests within integrated circuits.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, an integrated circuit 11 includes a pair of complementary transistors Q11. Q12 is formed. These transistors Q11. A common emitter connection point of Q12 is connected to an external connection terminal 18 of the integrated circuit 17.

The bases of the transistors Qll and Q12 are connected to input terminals 19°20 to which the first and second signals are supplied.
are connected to each. Further, the collector of the transistor Q12 is connected to a power supply terminal 21 to which a DC voltage CC is applied. In addition, the above transistor Q
The collector of No. 11 is grounded.

Furthermore, the transistor Q11. A common emitter connection point of Q12 is grounded via a resistor R11.

On the other hand, outside the integrated circuit 17, the external connection terminal 17 is connected to the DC voltage VC via the resistor R12 and the switch 22.
It is connected to the N8 terminal 23 to which C is applied, and is also connected to a signal input circuit (not shown).

Here, it is assumed that the DC level of the first signal is set higher than the DC level of the second signal.

First, when the switch 22 is off, the transistor Q
12 becomes active as an emitter follower, and transistor Q11 becomes inactive, so external connection terminal 1
A second signal is output from 8.

Next, when the switch 22 is in the on state, the DC bias current ■1 supplied to the external connection terminal 18 is applied to the integrated circuit 1.
If set to be sufficiently larger than the DC bias current 2 in 7, the transistor Q12 becomes inactive and the transistor Q11 becomes active as an emitter follower, so the first signal is output from the external connection terminal 18. Output.

FIG. 2 shows a modification of the above embodiment, in which transistors Q11. Connect the common emitter connection point of Q12 with a resistor R.
11 to the II source terminal 21, and the external connection terminal 18 is grounded via a resistor R12 and a switch 22. In this case, if the DC level of the first signal is set higher than the DC level of the second signal, the same operation as in the above embodiment can be performed.

Moreover, FIG. 3 shows a modification of FIG. 2, in which the external connection terminal 18 is connected to the power supply terminal 23 via a resistor R12a and a switch 22a, and is grounded via a resistor R12b and a switch 22b. are doing. .

In this case, the DC bias current supplied to the external connection terminal 18 is switched in a complementary manner, that is, the switch 22a,
By switching on and off 22b in reverse, the first and second signals can be selectively output from the external connection terminal 18 in the same manner as described above.

Here, FIG. 5 shows an example of implementation in which the present invention is applied to an integrated circuit 24 of a color television receiver. That is, in this integrated circuit 24, in addition to various circuits such as an ACC (automatic high gain m> circuit 25, a chroma amplification circuit 26, a color density adjustment circuit 27, and a color demodulation circuit 28), for example, the signal switching circuit shown in FIG. A circuit 29 is formed.

In this case, the output of the color demodulation circuit 28 and the output of the chroma amplification circuit 26 are supplied to the signal switching circuit 29 as first and second signals, respectively.

Further, the output of the signal switching circuit 29 is connected to an external connection terminal 30.
The signal is led out to the outside of the integrated circuit 24 via. At this time, the signal switching circuit 29 corresponds to turning off the switch 22 in FIG. 1, so the second signal, that is, the output of the chroma amplifier circuit 26, is taken out from the external connection terminal 30. .

When testing the quality of the integrated circuit 24, a DC voltage Vcc is applied to the external connection terminal 30 via the resistor R12. This corresponds to turning on the switch 22 in FIG.
The signal, that is, the output of the color demodulation circuit 28, can be taken out and measured.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] Therefore, as described in detail above, according to the present invention, it is possible to reduce the number of used elements and the number of external connection terminals, thereby reducing the size of the integrated circuit. It is possible to provide an extremely good signal switching circuit that can contribute.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the signal switching circuit according to the present invention, FIG. 2 is a circuit diagram showing a modification of the same embodiment, and FIG. 3 is a modification of the circuit shown in FIG. 2. FIG. 4 is a block diagram showing an implementation example in which the present invention is applied to an integrated circuit of a color television receiver, and FIG. 5 is a circuit diagram showing a conventional signal switching circuit. 11... Integrated circuit, 12... External connection terminal, 13
...Switch, 14...Input terminal, 15...Terminal for external connection, 16...Input terminal, 17...Integrated circuit, 18...Terminal for external connection, 19, 20... Input terminal, 21...Power terminal, 22...Switch, 23.
...Power terminal, 24...Integrated circuit, 25...ACC
Circuit, 26... Chroma amplification circuit, 27... Color density adjustment circuit, 28... Color demodulation circuit, 29... Signal switching circuit, 30... Terminal for external connection. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) Each emitter is commonly connected to an external connection terminal,
A pair of complementary-connected transistors whose bases are supplied with first and second signals having different DC levels are integrated into an integrated circuit, and whether or not a DC bias current is externally applied to the external connection terminal. A signal switching circuit configured to selectively obtain the first and second signals from the external connection terminal in accordance with the above. (2) the first and second signals are signals to be measured that are processed and generated by a circuit formed within the integrated circuit;
2. The signal switching circuit according to claim 1, wherein the signal switching circuit is selectively taken out from the external connection terminal for measurement.