BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram illustrating a signal switching circuit according to an embodiment of the present invention;
FIG. 2 is a circuit diagram illustrating a situation where a connection state of the signal switching circuit of FIG. 1 is switched; and
FIG. 3 is a circuit diagram illustrating an example of a conventional signal switching circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, a signal switching circuit according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIGS. 1 and 2 illustrate the signal switching circuit according to the embodiment, showing a situation where a connection state is switched.
As illustrated in FIGS. 1 and 2, the signal switching circuit according to the embodiment includes an input terminal 1 to which a signal is input, an output terminal from which a signal is output. A first electronic circuit 3 and a second electronic circuit 4 are provided to be alternately connected between the input and output terminals 1 and 2. In addition, the switching elements 5a and 5b for alternately connecting one of the electronic circuits 3 and 4 between the input and output terminals 1 and 2 through a selection. For the switching elements 5a and 5b, a relay, an FET switch, a diode switch, and the like may be used. The switching elements 5a and 5b are configured to be switched in response to an external control voltage. Furthermore, a signal alternative path 6 for connecting the input and output terminals 1 and 2 therebetween at all times is provided between those terminals. Also, the electronic circuit 3 as one of the electronic circuits 3 and 4 is a through circuit formed in such a manner that no change is imparted on the signal input to the input terminal 1 and the signal is propagated as it is to the output terminal 2. The electronic circuit 4 as the other electronic circuit is provided with two resistors 7a and 7b which are respectively connected to the input and output terminals 1 and 2 when the switching elements 5a and 5b are connected thereto. The signal alternative path 6 has a resistor 6a that is connected in parallel to a signal path connecting between the input and output terminals 1 and 2. Then, the resistors 7a and 7b of the electronic circuit 4 and the resistor 6a of the signal alternative path 6 constitute a part of a circuit for completing a p-type resistance attenuation circuit which is an embodiment of a resistance attenuation circuit, when both the switching elements 5a and 5b are connected to the electronic circuit 4 side.
Next, operations of this embodiment will be described with reference to FIGS. 1 and 2.
FIG. 1 illustrates a state where both the switching elements 5a and 5b are connected to the through circuit of the first electronic circuit 3. In this connection state, no change is imparted on the signal that is input to the input terminal 1. The signal passes the through circuit as it is and is propagated to the output terminal 2. Then, the signal is output to an electronic circuit or the like (not illustrated in the drawing) in a later state.
From this connection state of FIG. 1, an external control voltage is used to switch the connection of the switching elements 5a and 5b from the first electronic circuit 3 to the second electronic circuit 4. This switching time is as short as only approximately several nano seconds to several micro second.
According to the signal switching circuit of this embodiment, the signal alternative path 6 is connected between the input and output terminals 1 and 2 at all times. Thus, even at the switching time when both the switching elements 5a and 5b are put into the open state for about several nano seconds to several micro second, the signal that is input to the input terminal 1 is output to the output terminal 2 via the signal alternative path 6. Therefore, the signal is not discontinued even at the moment of the connection switching, whereby it is possible to propagate the signal with certainty at all times. Also, according to the signal switching circuit of this embodiment, even in the case of a digital signal which imparts a large influence on a signal process in a later stage if the propagation of a signal that should be propagated is discontinued, even at the moment when the connection of the first and second electronic circuits 3 and 4 is switched by the switching elements 5a and 5b, the signal is not discontinued at all and the signal can be propagated with certainty at all times.
Furthermore, when the second electronic circuit 4 is connected through the selection by the switching elements 5a and 5b, the resistor 6a of the signal alternative path 6 connected in parallel to the signal path and the resistors 7a and 7b of the second electronic circuit 4 constitute the p-type resistance attenuation circuit as the resistance attenuation circuit. As a result, the signal can be propagated and output to the output terminal 2 while being subjected to a reliable attenuation effect.
Furthermore, according to the signal switching circuit of this embodiment, with the provision of the resistor 6a in the signal alternative path 6, the resistance attenuation circuit can be completed through the use of combination options of the resistors 7a and 7b of the first and second electronic circuits 3 and 4, whereby it is possible to achieve a simplification and a miniaturization of the configuration of the signal switching circuit itself.
It should be noted that the present invention is not limited to the above-described embodiment and can be modified in various modes as necessary.
Patent Application
20070252634
