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DESCRIPTION OF THE PREFERRED EMBODIMENT Mode Switching Circuit Between the first
channel path and the second channel path, an @ 1 and a second mode switching switch are
provided, and between the common connection path of the first and second mode switching
switches and the ground. And a resistor is inserted in the circuit to eliminate the adjustment to
the parasitic capacitance signal generated in the common connection path of the first and second
mode changeover switches.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mode switching
circuit suitable for use in switching between a plurality of operation modes such as stereo /
monaural switching. Various kinds of such mode switching circuits have been proposed
conventionally, but FIG. 1 shows an integrated circuit designed to process audio signals, which
incorporates, for example, a configuration for switching stereo and monaural as such mode
switching circuits. An example is shown roughly. That is, in FIG. 1, on the screen, for example, the
left side represents the R channel and the right side represents the R channel portion, and (IL),
(2L) and (3L) represent the phono input terminal for the R channel, and a line such as a tuner.
Input terminals and auxiliary input terminals, each input terminal (IL) + (2L) and (3L) being an L
channel via input signal selector switches (4L), (5L) and (6L) The phono input terminal (IR) for
the R channel that is connected to the output terminal (7L). The line input terminals (second
auxiliary and auxiliary input terminals (3R) are similarly connected to the R channel output
terminals (7R) K via input signal changeover switches (4R), (5R) and (6R), respectively. In
addition, mode switching switches (8) and (9) which are simultaneously turned on and off are
provided between the R channel path and the R channel path in order to make the signal system
symmetrical. Then, when listening as stereo, open these switches (8) and (9) to separate both
channel paths, and show the L channel signal and R channel signal taken out to the output
terminals (7L) and (7R) respectively. Not shown, let's release EndPage: 1 sound from the speaker
through the control circuit etc. The same applies to the mode of picking up or testing either L
channel or R channel. On the other hand, when listening as monaural, the switches (8) and (9)
are simultaneously closed to take out the mixed signal of the L channel signal and the L channel
signal to the output terminals (7L) and (7R), respectively. By the way, when the mode switching
circuit is incorporated in the integrated circuit as described above, the part between the switch
(8) and the switch (9), that is, the contact (8a) of the switch (8) and the contact (9a) of the switch
(9) (Hereinafter referred to as a common connection path) (1 (i is generally wired with an
aluminum material). Accordingly, in stereo mode, the common connection path II is completely
isolated by opening the switches (8) and (9), so that the function close to the common connection
path 'II is between the substrate αD at a predetermined negative potential. Charges are
accumulated in the parasitic capacitances oz and 03 shown typically by two.
It is also considered that charges jumping from peripheral conductive paths are also accumulated
in these parasitic capacitances tO3 and α3 regardless of the opening and closing of the switches
(8) and (9). The accumulated charge is discharged when the switches (8) and (9) are closed, that
is, at the time of switching from stereo to monaural, so this is superimposed as a noise current on
the signal system and output. That is, since so-called switching noise is generated by the
discharge of the parasitic capacitances tI2 and α3, it becomes extremely annoying to the
listener. The present invention has been made in view of the above-mentioned problems, and
provides a high-performance mode switching circuit in which the settling of the above-mentioned
switching noise and the like is eliminated. An embodiment of the present invention will be
described in detail based on FIG. 2 by taking the case where the mode switching circuit is
incorporated in an integrated circuit as in FIG. 1 as an example. In FIG. 2, parts corresponding to
FIG. 1 are given the same reference numerals, and the detailed description thereof will be
omitted. In this embodiment, both ends of the common connection path 0I are grounded
symmetrically using resistors I and Q5, respectively. The resistors (141 and (151 may be used
here as components of the integrated circuit and have a value such as several tens to 100 GΩ /
Sq that does not affect the signal system. Therefore, parasitic capacitance rI? (The charge stored
in '131 K will always be discharged through resistors H and a 51, respectively, so even if
switches (8) and (9) are closed, the switching as described in FIG. According to the present
invention, as described above, according to the present invention, the common connection path
of the switches symmetrically disposed between the plurality of channel paths is grounded via
the resistor, and the switch common To discharge the charge accumulated in the parasitic
capacitance between the connection path and the substrate constantly! III, no switching noise or
the like occurs even at the time of mode switching, that is, when the switches (8) and (91 are
closed), so that the mode switching circuit with excellent performance can be obtained. Although
the above embodiment has been described by taking the case of the mode switching circuit in
which the present invention is incorporated in an integrated circuit as an example, the present
invention is not limited to this and can be similarly applied to so-called conventional discrete
circuits. It's too late. In the above-described embodiment, although (5) the number of resistors
connected between the common connection path a1 and the ground (5) has been described in
connection with two cases, it is possible to maintain the symmetry of the signal system of the
corresponding channel. It may be good or two or more.
Furthermore, although the adverse effect of the parasitic capacitance on the signal has been
described as so-called switching noise in the above description, it goes without saying that other
adjustments due to such parasitic capacitance can be similarly eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing one example of a
conventional mode switching circuit, and FIG. 2 is a circuit diagram showing one embodiment of
the present invention. + 81, (91 is a mote switch, OI is a common connection path, OD is a
substrate, az, a: i is a parasitic capacitance, and at +, a is a resistor. EndPage: 2