JPS59224982A - Signal automatic switching circuit - Google Patents

Abstract

PURPOSE:To form a signal automatic switching circuit on the same IC of a liquid crystal display device by forming the signal automatic switching circuit by means of an MOSFET. CONSTITUTION:When a signal to an input terminal 1 is active and a signal to an input terminal 6 is at a low level, the peak value of the signal applied to the input terminal 1 is held in a capacitor 22. Then an FET24 is turned on, an FET28 is turned off, a gate of an FET32 goes to high and a gate of an FET33 goes to low and the signal from the input terminal 1 is extracted from an output terminal 18. When the signal to the input terminal is at a low level and the signal to the input terminal 6 is active next, the peak value of the signal applied to the input terminal 6 is held in a capacitor 26. Then the FET24 is turned off, the FET28 is turned on, the gate of the FET23 goes to low and the gate of the FET33 goes to high level and the signal from the input terminal 6 is extracted from the output terminal 6. The signal automatic switching circuit is formed on the same IC as that of the liquid crystal display device.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic signal switching circuit used in liquid crystal display devices and the like.

BACKGROUND ART AND PROBLEMS THEREOF For example, a video camera is provided with a signal switching circuit that selects whether a viewfinder display is a video signal from the camera or a video signal from a VTR. In this case, conventionally, for example, a circuit using bipolar transistors as shown in FIG. 1 has been used.

In the figure, an input terminal (1) to which a video signal from a camera (not shown) is supplied is connected to the base of a transistor (2). The collector of this transistor (2) is connected to the power supply terminal Vcc, and the emitter is connected to the resistor (
3) and is grounded through the constant current source (4), and this resistor (
3) and the constant current source (4) is connected to the base of one differentially connected transistor (5).

An input terminal (6) to which a video signal from a VTR (not shown) is supplied is connected to the base of a transistor (7). The collector of this transistor (7) is the power supply terminal V
cc, and the emitter is grounded through a resistor (8) and a constant current source (9), and the connection point between the resistor (8) and the constant current source (9) is differentially connected to the other side. is connected to the base of the transistor α0).

Furthermore, the input terminal (6) is grounded through a resistor (11), a diode (12), and a capacitor (13), and the midpoint between the diode (12) and the capacitor (13) is connected to the resistor (14), (15). ) in Schif ground sale,
A midpoint between the resistors (14) and (15) is connected to the base of the transistor (16). This transistor (
Between the collector and emitter of 16) is a 1-transistor (5)
connected between the base and ground.

Further, a connection point between the emitters of the transistors (5), 00) and a constant current source (17) is connected to an output terminal (1B) connected to a viewfinder (not shown).

In this circuit, when the transistor (16) is off, the video signal from the terminal +11 is supplied to the transistor (5), and if there is a signal at the terminal (6), it is supplied to the transistor (5). A signal is taken out to terminal (1B). On the other hand, when a video signal is supplied to the terminal (6), this signal is supplied to the transistor 00) and peak-held by the diode (12), capacitor (13), etc., and this hold signal causes the transistor ( 16) is turned on. A transistor for this purpose (5
) is cut off, and the signal supplied to the transistor (10) is taken out to the terminal (18).

In this way, the video signals from the ζ camera and VTR are switched and supplied to the viewfinder.

By the way, the use of a liquid crystal display device in a view finder is about to be put into practical use.

In that case, the driving circuit 71 of the liquid crystal display device is generally composed of MO3I transistors;
As mentioned above, it is difficult to simultaneously form circuits using bipolar transistors on a single IC chip.

Therefore, only the switching circuit is a separate IC, which is disadvantageous in terms of the number of terminals and space.

OBJECTS OF THE INVENTION In view of these points, the present invention enables an automatic signal switching circuit to be formed on the same IC-1 as a liquid crystal display device.

Summary of the Invention The present invention provides a plurality of input terminals, means for peak-holding signals supplied to these input terminals, and comparing these peak-held signals using a differential circuit to detect active inputs. means for detecting the above, l/transmission gates respectively provided at the plurality of input terminals, and these transmission gates are controlled by the detection signal from the detection means to selectively control the active human power. According to this automatic signal switching circuit, the automatic signal switching circuit can be formed on the same IC as a liquid crystal display device.

In the embodiment of FIG. 2, the input terminal (1) is connected to the gate of the MO3I-transistor (21). This transistor (
The drain of 21) is connected to the power supply terminal VDD, the source is grounded through a parallel circuit of a capacitor (22) and a minute constant current source (23), and this source is differentially connected to one MO3L run transistor) connected to the gate.

Further, the input terminal (6) is connected to the gate of the MOS transistor (25). The drain of this transistor (25) is connected to the power supply terminal M DI), the source is grounded through a parallel circuit of a capacitor (26) and a minute constant current source (27), and the source is connected to the other side which is differentially connected. is connected to the gate of MO3I-transistor (2B).

A connection point between the sources of these transistors (24) and (2B) is grounded through a constant current source (29). In addition, the drains are Mos+ transistors (30) and (31), respectively.
) is connected to the power supply terminal V l1l ) through a load consisting of V l1l ).

In addition, the input terminals (11, (6) are connected to a transmission gate consisting of MO3I-ranjisku (32), (33), respectively. Also, the transistors (24), (2
8), (30) and (31) are connected to the gates of transistors (32) and (33), respectively. The output sides of these transistors (32) and (33) are connected to lr, and the midpoint of this connection is connected to the output terminal (18).

In this circuit, a transistor (21), a capacitor (22), a current source (23) and a transistor (25)
), the capacitor (26), and the current selection (27) each constitute a peak hold circuit.

For example, if the signal at the input terminal Ifi+ is active and the input terminal (6)'s input signal 1F3 is low, the capacitor (22) will have the signal input to the input terminal (1) in bold. , and the second capacitor (26) are at ground potential. Therefore, the transistor (24) is turned on,
(2B) is turned off, and the gate I of transistor (32) is turned off.
・is high, the gate of (33) is low, and the input terminal (
The signal from 1) is taken out to the output terminal (1B).

Next, when the signal at input terminal +11 becomes low and the signal at input terminal (6) becomes active, the peak held in the capacitor (22) is discharged through the current source (23), and the capacitor (26) receives the input signal. The peak value of the signal supplied to the terminal (6) is held. Therefore, the transistor (24) is turned off, the transistor (28) is turned on, the gate of the transistor (32) is low, and the gate of (33) is low. When the signal becomes high, the signal from the input terminal (6) goes to the output terminal (18).
It is taken out.

In this manner, in this circuit, only the activated signal among the signals supplied to the input terminals (1) and (6) can be selectively taken out to the output terminal (18).

In this case, since each transistor is composed entirely of ζ MO3, these can be formed in the same rc- and t- as the liquid crystal display device. Furthermore, since the capacitors (22) and (26) only need a small capacity, all the circuits including these can be formed simultaneously on a single IC chip.

Furthermore, FIG. 3 shows other examples. In the figure, transistors (30) and (31) are active negative transistors using depletion type MOS transistors.

This increases the gain of the differential amplifiers such as the ζ transistors (24) and (28), and this circuit operates as a comparator. Furthermore, the transmission gates of the transistors (32) and (33) are each configured to have a CMO5 configuration. The signal from the comparator is then supplied to each gate in reverse phase.

In this circuit, the transmission gate is CMO
5 configuration, the signal transmission region is between the voltage #i and the ground potential, so that the transmission characteristics are improved.

Further, in the above example, both transistors (21) and (25) have a source follower configuration, but they may also be diode-connected as shown in FIG.

Further, in the above example, a case was described in which only one of the input signals is active, but in a case where both are active at the same time and priority is given to one of the input signals, for example, as shown in FIG. 5 below.

That is, in the figure, the input terminal +11 is connected to the gate of the MOS transistor (41), and the input terminal +11 is connected to the gate of the MOS transistor (41).
The drain of 1) is connected to the power supply terminal VDD, the source is grounded through a resistor (42) and a constant current source (43), and the connection between this resistor (42) and constant current source (43) is a transistor. It is connected to the gate of (21).

As a result, the signal from the input terminal Tll is lowered in potential by a predetermined value and is supplied to the transistor (21), and when both signals become active, the signal from the input terminal (6) is prioritized.

Another way to prioritize is to use transistors (
21) may be formed as an enhancement type element, and (25) may be formed as a depression type element. In this case, the input terminal (6) is given priority. Or a transistor (24),
The threshold voltage of (28) may be changed.

Furthermore, in the above-mentioned circuit, even when three or more human forces are required, switching can be performed by providing a subordinate differential circuit.

Further, the above-described circuit can be applied not only to crystalline silicon but also to TPTJi circuits using amorphous silicon, Te, etc.

Effects of the Invention According to the present invention, an automatic signal switching circuit can be formed on the same IC as a liquid crystal display device.

[Brief explanation of drawings]

FIG. 1 is a connection diagram of a conventional circuit, FIG. 2 is a connection diagram of one example of the present invention, and FIGS. 3 to 5 are connection diagrams of other examples. Ill, (6) is the input terminal, (18) is the output terminal, (2
1), 0 (24), (25), (2 days), (30) ~ (33)
are MOS transistors, (22) and (26) are capacitors, and (23) and (27) are minute constant current sources. Book Figure 3 Figure 9 Figure 5

Claims (1)

[Claims] a plurality of input terminals, means for peak-holding signals supplied to these input terminals, and means for comparing these peak-held signals using a differential circuit to detect an active input; A signal for selectively extracting the active input by controlling the transmission gates provided at each of the plurality of input terminals and the transmission gate 1 by the detection signal from the detection means. Automatic switching lid.