JPS6012832B2 - scanning circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of configuring a simple and inexpensive scanning circuit for sequentially scanning a large number of loads connected in an XY matrix and detecting the current of each load.

As is well known, scanning methods for sequentially scanning a large number of loads connected in a matrix can be roughly divided into a load power supply type scanning method and a load current detection scanning method.

Examples of the former are the voltage-generating scanning method for scanning printed multi-needle electrode plates used in facsimile reception and recording systems, and the energizing type for scanning thermal recording heads that are also used in reception and recording systems. There are scanning methods. An example of the latter is a method of scanning a two-dimensional solid-state image sensor used in a photoelectric conversion system such as a television camera.
Although this method is the same as the energized scanning method for loads within the matrix, it necessarily requires one or more external loads for current detection. FIG. 1 shows the switch portion of the subordinate scanning circuit of each of the above systems.

In the figure, numerals a to e are power supply type scanning circuits, particularly modified examples to the load current detection type, and 1 is a load current detection type scanning circuit. By the way, a has disadvantages such as the need to configure the Y-side switching transistors TR, TR2 with push-pull, etc., the large number of transistors used, the large circuit scale, and the lack of economic efficiency. are doing. In b and c, the XY control signals are inverted, so it is necessary to invert the X side or the Y side of the outputs of the two sets of decoders that respectively decode the contents of the xY scanning power counter. Since d becomes active when the XY side control signal is at /.i level, when a TTL decoder is used as a decoder, its output must be inverted. e is active when the XY control signal is low level and can be directly connected to the TTL decoder, but it is necessary to set the power supply voltage Eo when the Y side control signal is not selected (high level), so
This is especially disadvantageous when the load resistance value is large. The same can be said for case b. Furthermore, all of b to e require a large number of transistors and resistors, and have the disadvantage that they are easily affected by variations in hfe of the transistors. On the other hand, since a switching transistor is required for each load f', it is only possible to implement it by making it into an LSI, but it is still expensive at present. The present invention belongs to the load current detection type scanning method, and by using a switch element such as a TTL open collector integrated on both the X side and Y side and an external blocking diode on the X or Y side, the matrix when not selected is The object of the present invention is to implement a simple and inexpensive scanning circuit by bypassing the internal bias current and the same load current to an external load.

Hereinafter, the present invention will be explained in detail with reference to the drawings. Figure 2a
1 is a diagram illustrating the principle of the present invention, and shows only a switch portion for an arbitrary load Rij among a large number of loads connected in a matrix.

In the figure, 1 is a DC power supply, 2 is a protective resistor, 3 is a load Rij in the matrix, 4 is an external load resistor RL for current detection, 5 and 6 are X and Y side switches, respectively, and 7 is an external blocking diode. . Figure b shows an example in which the switches 5 and 6 in figure a are implemented with transistors, and 8 and 9 are resistors of approximately several KQ connected in series to the bases of the transistors, which are directly connected to the TTL decoder. It is something. In addition, the same figure c shows the switch 5 in figure a,
6 is realized by a TTL open collector/inverter, and the input side of the TTL inverter is directly connected to a TTL decoder. Next, Figure 2 b or c
To operate the floating diode, control signals xi and yj are both set to low level only when load Rij is selected, and switches 5 and 6, which are transistors or TTL open collector inverters, are turned off. 7 to allow the load current to flow to the external load RL.

When not selected, the current to the external load RL is bypassed by setting at least one of the control signals xi and yj to a high level. Here, the external blocking diode 7 functions to prevent the load current from being bypassed by the X-side switch Xsi when the load Rij'(i') is selected. FIG. 3 shows an overall configuration diagram of the scanning circuit of the present invention.

That is, FIG. 3 shows the X-side selection lines X, ~Xm and the Y-side selection lines Y, which have m×n loads wired in a matrix.
~ Yn are connected through diodes to each intersection, and one end of each of the X and Y side selection lines is connected to a switching element such as the TTL open collector described in FIG. 2 (for convenience, only ×S, , YS. ) are connected, and each other end of the X side selection line is connected to a protective resistor R,, R2,...
...Connected to the DC power supply +Eo through Rm, and each other end of the Y side selection line is connected to an external blocking diode D,...
It has a configuration in which it is connected to an external load resistor RL for current detection through D2, . . . Dn. In addition, A.M.
The circle is an obeamp. When not selected, × side selection line X, ~×
All switch elements connected to m and Y side selection lines Y, -Yn are in a conductive state.

For example, loads R, . When selecting , only the switch elements xs, ,Ys, are made non-conductive. At this time, the load current is DC power supply + Eo - protection resistor R, one load R, . - flocking diode D, - external load resistance R. That is, the load current is connected to the Y side selection lines Y2 and Y3.
, . . . Yn is prevented by the floating diodes D2, D3, . . . Dn. The current flowing through the external load resistor RL is detected by the oven amplifier AMP and appears at the output terminal OUT. In FIG. 3, if the load Rij is made of a photoconductor such as CdS, the load assembly can function as a solid-state photoelectric conversion device.

In this case, a decrease in load resistance Rij due to light intensity is detected by converting the current. In addition, since it is quite large, about the bright resistance MQ with a small area CdS, the x-side protection resistances R, ~Rm can be made sufficiently large, and the power consumption of the non-selected portions can also be made sufficiently small. Further, the photocurrent amplification section in this case is constituted by an operational amplifier, and receives the voltage from the external load RL through a high-impedance positive input, resulting in an extremely simple amplification circuit configuration. Also, if the power supply voltage 1Eo is 5V, the × side switch is a standard TTL (totem pole output type)
is also available. FIG. 4 shows an example of a scan control circuit when m=n=16.

In the figure, 11 is an X-side scanning/binary counter that is incremented by a clock pulse Cp, and 12 and 13 are Y-side scanning binary counters whose advancement is controlled by the carry signal of the x-side scanning counter 11. It is. 14 and 1
5 is an X-side decoder that decodes the output of the X-side scanning counter 11; 16 and 17 are Y-side scanning counters 12 and 13;
This is a Y-side decoder that decodes the output of.

18 is a TTL open collector inverter group on the X side which is controlled to be conductive or non-conductive by the outputs of the decoders 14 and 15; 19 is similarly conductive by the outputs of the decoders 16 and 17;
This is a Y-side TTL open collector inverter group that is controlled to be non-conductive.

Reference numeral 20 represents a group of protective resistors, and 21 and 22 represent groups of external blocking diodes.

All the parts shown in FIG. 4 can use standard general-purpose package parts, which is highly economical. Furthermore, in the embodiment, the inverter groups 18 and 19 have six circuits/package, and the circuit area of this portion is significantly reduced compared to the case where individual transistors are used. Note that if the voltage of the power supply Eo needs to be increased or if the load resistance is 4.
- If it is necessary to reduce the protection resistance and the external load resistance, a high breakdown voltage, large sink current open collector TTL may be used as the inverter group 18, 19. In this case, the cost of the inverter portion will be approximately double, but since the inverter is originally extremely inexpensive, the economic efficiency of the scanning circuit will not be affected. As described above, according to the present invention, when scanning a collection of loads connected in a matrix in a wide range of applications, it is possible to realize a scanning circuit with an extremely simple configuration and excellent economic efficiency.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a switch portion of a conventional scanning circuit, FIG. 2 is a diagram showing the principle configuration of the present invention, FIG. 3 is a diagram showing an embodiment of the scanning circuit of the present invention, and FIG. FIG. 3 is a diagram showing an embodiment of the same scanning control circuit. 1...Power supply, 2...Protection resistor, 3...
...Load, 4...External load resistance for current detection, 5
, 6... Switch element, 7... External blocking diode. False Mu9 Figure 1 Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. A first selection line group and a second selection line group are connected through loads, and a first scanning switch is connected to one end of each selection line of the first selection line group. and the other end is commonly connected to a DC power supply through a protective resistor, and the second
A second scanning switch is connected to one end of each selection line of the selection line group, and the other end is commonly connected to a load current detection resistor through an external blocking diode, and the first and second scanning switches are connected to each other. A scanning circuit characterized in that it is in a conductive state when not selected and in a non-conductive state when selected. 2. The scanning circuit of claim 1, wherein the first and second scanning switches are integrated TTL open collector inverters.