JPS622728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching signal detection circuit suitable for an integrated circuit in a circuit that requires system mode switching, such as a VTR that switches circuit operation in recording/playback mode. be.

Two modes by conventional integrated circuits e.g.
How to switch between recording and playback on a VTR:
Two power supply voltages corresponding to each mode are
A method is used in which integrated circuits are supplied from two lead-out terminals, or a method in which a power supply voltage is supplied through one lead-out terminal and a switching signal is inputted through another lead-out terminal. In integrated circuits, 1 is used for power supply.
Since two lead-out terminals are required, either method uses at least one dedicated terminal for inputting the switching signal.

An object of the present invention is to provide an integrated circuit using a switching method that does not require a dedicated extraction terminal for switching signals.

In order to achieve the above object, the present invention applies the mode switching signal to one of the signal output terminals from the integrated circuit, so that the input terminal for the mode switching signal and one of the signal output terminals are shared. The present invention is characterized in that a circuit that turns on and off according to the input mode switching signal is provided to reliably detect the mode switching signal, without providing a dedicated terminal for the mode switching signal.

The present invention will be explained below with reference to Examples.

FIG. 1 is a circuit diagram of a main part of an integrated circuit showing an embodiment of the present invention, in which a mode changeover switch SW is provided between a power supply voltage application terminal 3 and a signal output terminal 4 from the integrated circuit 1. As shown in FIG. When the contact of the changeover switch SW is set to the A side, the transistor Tr ₁ operates as an emitter follower, and the signal supplied to the base is output from the emitter through the transistor Tr ₂ to the terminal 4, and then sent to other circuits via the capacitor C. is supplied to The bases and emitters of the transistors Tr ₂ and Tr ₃ are commonly connected to form a current mirror circuit, and the collector of the transistor Tr ₃ is connected to the current I ₁ of the current source 2 flowing to the collector of the transistor Tr ₂ . A current I ₂ equal to the sum of the AC signal current flowing through the terminal 4 flows. This current I ₂ generates a diode forward voltage V in the two diodes D ₁ and D ₂ , so the terminal 7 has a voltage of 2V.
voltage appears.

When the contact of the changeover switch SW is connected to the B side and the power supply voltage Vcc is applied to the terminal 4, the bases of the transistors Tr ₂ and Tr ₃ are at the potential of the power supply voltage Vcc, so the two transistors Tr ₂ and Tr ₃ are Cut off both. At this time, the current flowing from current source 2
_I1 flows directly from the power supply connected to the power supply voltage application terminal 3 through the changeover switch SW.
Since the transistors Tr ₂ and Tr ₃ are cut off, no current flows through the diodes D ₁ and D ₂ , and the voltage at the terminal 7 becomes 0V. Therefore, 2V and 0V are applied to terminal 7 depending on the switching of the contacts of the changeover switch SW.
Two states are obtained, which can be applied to a circuit in the integrated circuit 1 that requires mode switching and used as a signal for mode switching.

In this case, if the contact of the changeover switch SW is on the A side, it is mode 1, and when it is on the B side, it is mode 2.
In mode 2, as mentioned earlier, the transistor
Since Tr ₂ and Tr ₃ are cut off, the signal from transistor Tr ₁ is also no longer output from terminal 4. Therefore, a changeover switch for mode switching is required.
This will not be a problem if the terminal to which the SW is connected is the output terminal of a circuit that does not have a signal output in one mode or does not require a signal output.

Note that if it is necessary to increase the voltage appearing at the terminal 7 in mode 1 to a higher value, the number of diodes may be increased. Moreover, it is needless to say that this is not limited to a diode, and any element that causes a voltage drop, such as a resistor or a transistor, can be freely selected as required.

In Figure 1, the current mirror circuit is a transistor Tr ₁
Although it is connected to the emitter side, the same operation will be performed even if it is inserted to the collector side as shown in FIG. In the figure, 8 is a voltage drop element.

Furthermore, the same operation can be achieved by replacing the NPN transistor and PNP transistor shown in FIGS. 1 and 2, respectively, and the configurations shown in FIGS. 3 and 4, respectively, can be obtained. Conceivable. In these examples the toggle switch
SW is connected between terminal 4 and ground, and when switched to the contact B side, the current side to transistors Tr ₄ , Tr ₅ , and Tr ₆ is grounded, so each transistor Tr ₄ ,
Tr ₅ and Tr ₆ are cut off. Further, the voltage drop element 8 is not the ground terminal 5 but the power supply voltage application terminal 8.
connected to. Therefore, the voltage at terminal 7 generated in response to mode switching is such that one side is equal to the power supply voltage.
Vcc, and the other is the voltage obtained by subtracting the voltage drop caused by the voltage drop element 8 from the power supply voltage.

As described above, in the signal detection circuit for an integrated circuit according to the present invention, by superimposing a switching signal on the output terminal of one mode, different voltages can be generated in the integrated circuit according to the switching signal. ,
Furthermore, there is no need to provide a dedicated lead-out terminal for mode switching of the integrated circuit. Therefore, the number of lead-out terminals of the integrated circuit can be reduced, resulting in a significant cost reduction effect. Moreover, it is clear that its application is not limited to VTRs, but can also be widely applied to integrated circuits of systems that require mode switching.

[Brief explanation of the drawing]

1 to 4 are circuit diagrams showing embodiments of the present invention. 1... Integrated circuit, 2... Current source, 3... Power supply voltage application terminal, 4... Output terminal, 5... Ground terminal,
7... Terminal within the integrated circuit, 8... Voltage drop element,
SW...Mode changeover switch.

Claims (1)

[Claims] 1. A circuit that is selectively switched between at least two operation modes and operates differently depending on the mode; and a circuit that outputs a signal in one of the two operation modes and outputs a signal in the other mode. In an integrated circuit including an emitter follower and an output terminal constituting a circuit that does not require an emitter follower, a means for coupling the emitter of the emitter follower and the output terminal, a constant current circuit inserted in an emitter current path of the emitter follower, a switching means for applying a different DC voltage to the output terminal from outside the integrated circuit according to the operation mode to change the DC current flowing into or out of the output terminal; and a switching means inserted in series in the current path of the emitter follower; a signal detection circuit that detects a difference between a current value of the constant current circuit and a current value flowing into or out of the output terminal, and converts a change in this difference current, which changes according to switching of the switching means, into a voltage change; A signal detection circuit for an integrated circuit, characterized by comprising: 2. In the signal detection circuit for an integrated circuit according to claim 1, the signal detection circuit is connected to a current mirror circuit connected to the emitter circuit or collector circuit of the emitter follower, and to one current path of the current mirror circuit. 1. A signal detection circuit for an integrated circuit, comprising an inserted voltage drop element.