JPS602809B2 - multiplexer circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multiplexer circuit intended for analog inputs.

Such multiplexer circuits can be used to connect sensor heads of mark sheet readers using phototransistors, sensor heads of card readers, sensors of various parts of terminal equipment, measuring instruments and telemeters that handle multi-channel analog input, and base units and multiple slave units. It is widely used for interfon etc.

However, as shown in FIG. 1, the conventional analog input multiplexer circuit 100 decodes the select signal input from the select signal line 4, selects and takes in one of the multi-channel analog inputs 2, and is normally configured to be output on an output signal line 3 separate from the select signal line 4. Therefore, the number of signal lines between the device and the external device is large, causing high costs. In order to reduce the number of signal lines, this analog input multiplexer circuit uses an analog/digital converter to convert analog output signals and select signals into digital signals, and inputs and outputs both signals through a common signal line. An analog input multiplexer circuit has also been proposed in which both signals are placed on a common signal line by frequency division using a carrier wave. However, in such a configuration, the multiplexer circuit and its peripheral devices are extremely complex.
It is expensive and unsuitable for applications that handle the output of simple sensors. Therefore, an object of the present invention is to provide an analog input multiplexer which allows a digital signal that is selection control information and a selected analog signal to be placed on a common signal line, thereby reducing the number of signal lines between external devices. The purpose is to provide circuits.

However, the feature of the multiplexer circuit according to the present invention is that the multiplexer circuit selects either the analog signal on the first channel or the second channel in response to positive and negative select signals intermittently outputted to the signal line by an external device. a memory means, a decoder means for storing the polarity of the select signal appearing on the signal line in the closing memory means, and a decoder means for storing the polarity of the select signal appearing on the signal line in the closing memory means; It comprises an input selection circuit for selecting an input, and an input/output switching circuit interposed between the input selection circuit and the signal line, and the selection signal and the corresponding analog input signal are connected to the common signal line. The main point is that the input/output is made to the external device via the external device.

FIG. 2 shows a block diagram of a multiplexer circuit for analog inputs according to the invention. External signal line 5 from external device 27
A digital signal, which is a control signal, is intermittently sent out above. This digital signal is not transmitted to the input side 3 of the input/output switching circuit 8 but is bypassed to the input line 6 of the decoder 9. A decoder 9 creates a selection information signal 7 from the digital signal and temporarily stores it in a memory. In other words, memory 0 stores the previous select information signal 7 until the next select information signal 7 is input.The input selection circuit 2 channels analog input according to the select information signal 4 output from memory IQ. 2 and outputs it to the input line 3 of the input/output switching circuit 8. The input/output switching circuit 8 sends the analog input on the input line 3 to the external device 27 through the external signal line 5. A general serial interface can also be used for the content of the digital signal sent as a signal.
Alternatively, a simple positive/negative pulse may be used.

3. Next, an example of a specific configuration of the multiplexer circuit of the present invention shown in FIG. 2 and the input section of the external device 27 that controls the multiplexer circuit is shown and explained in FIGS. 3 and 4.
FIG. 3 shows three simplest examples of the multiplexer circuit.

The operational amplifier 19 to which negative feedback is applied by the resistor 17 and the tortoise 81 constitutes the input/output switching circuit 8 together with the resistor 28, and the pair of Zener diodes 16 constitutes the decoder 9. There is. The capacitor 15 acts as the memory 10, and the diodes 13 and 14, the phototransistor 11 receiving the analog input (light) of each channel, and the wire 2 constitute the input selection circuit 1. FIG. 4 shows an example of an input section of the external device 27.

The input line of the negative feedback amplifier circuit consisting of the operational amplifier 22 and resistors 25 and 26 is common to the signal line 5 of the multiplexer circuit. This signal line 5 is connected to transistors 23 and 24.
Connected to the positive and negative power supplies via. Next, the operation of the circuits shown in FIGS. 3 and 4 will be explained with reference to the time chart shown in FIG.

When the transistor 23 of the external device is turned on and a positive pulse voltage (control signal) is applied to the signal line 5, this positive pulse voltage becomes a positive pulse with an amplitude subtracted by the voltage drop of the Jenner diode 36. A voltage is applied to capacitor 5, thereby charging it in the positive direction (Vc in FIG. 5). Thus, the diode 13 and the phototransistor 11 become conductive, and the analog input (light) of the first channel enters the phototransistor single layer.
An analog signal corresponding to 1 is input to the input line 3, and thus the analog signal of the first channel is output to the signal line 5, as shown in FIG. Next, when the transistor 24 of the external device 27 is turned on and a negative pulse voltage (control signal) is applied to the signal line 5, the capacitor 15 is charged in the negative direction in the same manner as described above. In this way, the diode 4 and the phototransistor 12 become conductive, and an analog signal corresponding to the analog input (light) of the second channel is input to the input line 35, and is inverted and output to the signal line 5. The signal on the signal line 5 is inverted and outputted to the power receiving output terminal 21 of the external device 27. That is, after the transistors 23 and 24 are conductive, the analog signal on the signal line 5 is output to the output terminal 21 in the tri-state open state. Note that the two resistors shown in FIG. It has the effect of lowering the reverse gain of the direction circuit 8.The voltage value of the Jenner diode 6 is selected so that the analog signal output on the signal line 5 is not transmitted to the capacitor 5 side. As described above, the analog input multiplexer circuit according to the present invention can send and receive control signals (digital signals) and analog signals to and from external devices through a common signal line, and can significantly reduce the number of signal lines. It also has many advantages, such as being able to simplify the overall configuration as is clear from the embodiments described above.

[Brief Description of the Drawings] Fig. 1 is an explanatory diagram of the prior art, Fig. 2 is a block diagram showing the configuration of a multiplexer circuit according to the present invention, and Figs. 3 and 4 are specific examples of the multiplexer circuit according to the present invention, respectively. FIG. 5 is a circuit diagram showing a specific example of an input section of an external device connected to the multiplexer circuit, and FIG. 5 is a time chart for explaining the operation of the multiplexer circuit. 1...Input selection circuit, 2...-Analog input, 8...One-way circuit, 9...Decoder, 10...Memory. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 Connected to the external device 27 via the signal line 5, and outputs an analog signal on either the first or second channel according to the positive and negative select signals that the external device intermittently outputs to the signal line. a multiplexer circuit that selects a select signal, comprising memory means 10, 15, decoder means 9, 16 for storing in the memory means the polarity of the select signal appearing on the signal line, and a Input selection circuits 1, 11, 12, 13, 14 that select the input of either the first or second channel, and input/output switching circuits 8, 17 interposed between the input selection circuit and the signal line
20, wherein a select signal and a correspondingly selected analog input signal are input/output to an external device via the common signal line.