JPH0383370A - Signal inputting/outputting circuit - Google Patents

Abstract

PURPOSE:To provide a signal inputting/outputting circuit capable of inputting and outputting by one pin by outputting a signal to the pin in the form of a current signal in a signal outputting circuit and inputting a signal to the pin in the form of a voltage signal in a signal inputting circuit. CONSTITUTION:Since an emitter current of a transistor 12 is varied by a signal of a signal source 11 of an IC circuit 1, a current signal corresponding to a signal to be inputted to a base from the collector of the transistor 12 is outputted to a pin 8. The signal output to the pin 8 is inputted to a pin 9 of an IC circuit 2 through a signal line 30, and further input to the emitter of a transistor 21 of the circuit 2. When the current signal is inputted to the emitter of the transistor 21, the collector voltage of the transistor 21 is, since a constant-current source 23 is connected to the emitter, varied corresponding to the current signal input to the emitter, and a voltage signal is outputted from an output terminal 25.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a signal input/output circuit of an integrated circuit, and relates to the number of input/output pins.

(Prior Art) Conventionally, an integrated circuit (hereinafter referred to as an IC circuit) requires two pins: an output pin for outputting a signal to an external circuit and an input pin for inputting a signal from the external circuit. Figure 3 shows the case where analog signals are input and output between two IC circuits 1 and 2 of this type.Output pin P□ of IC circuit 1 and input pin P of IC circuit 2
I and the input pin P1 of the IC circuit 1 and the output pin P of the IC circuit 2. are connected with separate signal lines.

However, in FIG. 4, the signal output from the output pin P□ of the IC circuit 1 is output to the filter and signal processing circuit 5 consisting of the resistor 3 and the capacitor 4, and the signal that has passed through the filter and the signal processing circuit 5 is transmitted to the resistor. 6.7 and is returned into the IC circuit 1 from the input pin P■. in this case,
Despite the configuration in which the output signal of IC circuit #11 is returned to the inside of the IC circuit, the output pin P on the IC circuit. Two pins were required: and input pin Pr.

(Problem H to be solved by the invention) As mentioned above, in conventional IC circuits, one IC circuit requires two pins for signal input and one for signal output, and only a limited number of pins can be used. This was a disadvantageous configuration in terms of increasing the number of functions in circuits.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks and provides a signal input/output circuit that can perform input and output using a single pin.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a circuit that inputs and outputs signals and performs various processing, which includes one pin for connecting an external signal line, and a signal for outputting the signal to the pin in the form of a current signal. It has a configuration that includes an output circuit and a signal input circuit that inputs a voltage signal applied to the pin.As another configuration, in a circuit that inputs and outputs signals and performs various processing, external signals are input and output. It has a configuration that includes one pin for connecting a line, a signal output circuit that outputs a signal in the form of a voltage to the pin, and a signal input circuit that inputs a current signal input to the pin.

(Function) In the signal input/output circuit of the present invention, the signal output circuit outputs a signal in the form of a current signal to a pin to which an external signal line is connected. The signal input circuit inputs the voltage signal applied to the pin. As a further feature, the signal output circuit outputs a signal in the form of a voltage to the pin. The signal input circuit receives a current signal input to the pin.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a circuit diagram showing an example of the signal input/output circuit of the present invention. IC circuit with input/output pins 8.9, 8 is signal input/output pin of IC circuit 1, 9
are signal input/output pins of IC circuit 2, 11 and 24 are signal sources that generate signals, 12, 16, and 21 are transistors, 1
3.17.23 is a constant current source, 14 is a transistor 12
, 15.25 is the signal output terminal, and 22 is the collector resistance of the transistor 21.

Next, the operation of this embodiment will be explained. Pin 8 of IC circuit 1 and pin 9 of IC circuit 2 are connected by one signal line 30. First, the case where the signal from the ICC circuit signal source 11 is sent to the IC circuit 2 will be described. A constant current source 13 is connected to the collector side of the transistor 12, and the emitter is grounded via a resistor 14. Further, the base of this transistor 12 is grounded via the signal source 11. Therefore, since the emitter current of the transistor 12 is changed by the signal from the signal source 11, a current signal corresponding to the signal input to the base of the transistor 12 is output from the collector to the pin 8. The current signal output to pin 8 is input to pin 9 of IC circuit 2 via signal line 30, and further input to the emitter of transistor 21 of IC circuit 2.

On the other hand, the collector of the transistor 21 of the IC circuit 2 is connected to the voltage VCC via the resistor 22, and the emitter is connected to the constant current source 23. Furthermore, the bases of these two transistors are grounded via a signal source 24, forming a so-called common base amplifier circuit. Therefore, when a current signal is input to the emitter of this transistor 21, since the constant current source 23 is connected to this emitter as described above, the collector voltage of the transistor 21 corresponds to the current signal input to the emitter. Therefore, a voltage signal is taken out from the output terminal 25.

In the end, the signal current output from pin 8 of IC circuit 1 is I
This means that the signal is transmitted from pin 9 of C circuit 2 into this IC circuit 2.

Next, a case will be described in which a signal from the signal source 24 of the IC circuit 2 is sent to the IC circuit 1. Since the signal output from the signal source 24 is applied to the base of the transistor 21, the emitter current of the transistor 21 tends to change in response to this signal. However, since the constant current source 23 is connected to the emitter, a voltage change corresponding to the signal is generated at the emitter, and this is output to pin 9. The voltage signal output to pin 9 is input to pin 8 via signal line 30, and further input to the base of transistor 16 of IC circuit 1. The collector voltage of transistor 16 is voltage VC
C, and its emitter is grounded via a current source 17, forming a so-called emitter follower. Therefore,
A voltage signal corresponding to the voltage signal input to the base is generated at the emitter of the transistor 16, and this voltage signal is taken out from the output terminal 15. In the end, IC circuit 2
The voltage signal output from pin 9 of IC circuit 1 is output from pin 8 of IC circuit 1.
This means that the signal is transmitted from the IC circuit 1 to the IC circuit 1.

According to this embodiment, the IC circuit fY81 outputs a signal in current mode via pin 8, and inputs a signal in voltage mode via signal pin 8, and the IC circuit 2 outputs a signal in current mode via pin 8. By inputting a signal in current mode through pin 9 and outputting a voltage mode signal through pin 9,
The signal input/output pins for both IC circuits 1 and 2 are pins 8 and 8, respectively.
It can be one piece of pin 9. Therefore, IC circuit 1
Alternatively, one of the pins provided in the second pin can be used for another function, thereby facilitating the design of an IC circuit.

FIG. 2 is a circuit diagram showing another embodiment of the present invention. In this example, IC times Fl! Pin 8 of IC circuit 2 and pin 9 of IC circuit 2 are connected through a filter consisting of a resistor 31 and a capacitor 32, and the base of transistor 21 of IC circuit 2 is connected to the collector through signal processing circuit 26. This embodiment differs from the above embodiment in that the present embodiment is different from the above embodiment, but the other configurations are the same as the above embodiment.

Therefore, the signal from the signal source 11 in the IC circuit 1 becomes a current signal from the pin 8 and is output to the pin 9 side of the IC circuit 2.

In this case, the current signal is input to pin 9 via resistor 31, but is not affected by the filter function consisting of resistor 31 and capacitor 32. Therefore, the current signal input from pin 9 becomes a voltage signal from the collector of transistor 21 and is input to signal processing circuit 26 .

After processing the input signal, the signal processing circuit 26 applies the input signal to the base of the transistor 21 . Therefore, the transistor 21 outputs a voltage signal corresponding to the signal applied to the base from the emitter to the pin 9. In this case, the sum of the emitter voltage of the transistor 21 and the voltage generated by the current flowing through the resistor 31 and capacitor 32 is the IC
It will be applied to the base of transistor 16 via pin 8 of circuit 1. Here, the current flowing through the resistor 31 and capacitor 32 is the output current from the aforementioned pin 8 of the IC circuit 1. Therefore, at pin 8 of IC circuit 1,
This is the sum of the output current from pin 8 of IC circuit 1 filtered by resistor 31 and capacitor 32 and the signal processed by signal processing circuit 26, and this sum is the base of transistor 16 of IC circuit 1. will be applied to this IC circuit 1, and the fourth
The same operation as in the conventional example shown in the figure can be performed using pins 8.9 which serve both as input and output.

〔Effect of the invention〕

As described above, according to the signal input/output circuit of the present invention, input and output can be performed using one pin.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the signal input/output circuit of the present invention, Fig. 2 is a circuit diagram showing another embodiment of the invention, and Fig. 3 is a circuit diagram showing a conventional signal input/output circuit. Figure 4 shows an example of the connection between a pair of IC circuits having two pins for signal input and signal output, and an external circuit. This is a diagram. 1.2...IC circuit 8.9...Pin 11.24...Signal source 12.16.21...Transistor 13, ■7.23...Constant current source

Claims (2)

[Claims] (1) In a circuit that inputs and outputs signals and performs various processing,
It is characterized by comprising one pin for connecting an external signal line, a signal output circuit for outputting a signal to the pin in the form of a current signal, and a signal input circuit for inputting a voltage signal applied to the pin. signal input/output circuit. (2) In a circuit that inputs and outputs signals and performs various processing,
It is characterized by comprising one pin for connecting an external signal line, a signal output circuit for outputting a signal to the pin in the form of voltage, and a signal input circuit for inputting a current signal input to the pin. signal input/output circuit.