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科目：電気氏名：目代知子＜知的財産翻訳検定＞答案用紙★★★

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問 1.
Title of the Invention
Sound Volume Control Circuit and Method for Use in Portable
Car Phone and Like

Background of the Invention
Technical Field
The present invention relates to a sound volume control
circuit, and particularly relates to a sound volume control
circuit for use in a portable apparatus such as a car phone, etc.
Description of the Related Art
A portable car phone is used while it is installed in acar, and also while it is carried around.

An ordinary car phoneincludes a sound volume control circuit so that the user can makecalls at an optimum sound volume depending on the environmentof use when installed in the car or when carried around.

To bemore specific, when installed in the car, the car phone is usedwith its volume increased because of big environmental noise in1

the car, while when carried around it is used with the volume
reduced because there is no such big noise therearound.

However,conventional sound volum control circuits require volume
adjustment each time the use environment is changed.

Thisbothers users a lot when making phone calls, making them feelinconvenience in using the car phone.
In view of this situation, an object of the present
invention is to provide a sound volume control circuit which iseasy to use.
Another object of the present invention is to provide asound volume control circuit which does not require sound volume
adjustment each time the use environment of an apparatus ischanged

What is claimed is:1.

A sound volume control circuit comprising:means for amplifying an audio signal;
first and second holding means for holding a gain of said

amplifying means at first and second predetermined values
respectively;
status detecting means for detecting a usage status of anapparatus incorporating said sound volume control circuit andoutputting a status detection signal;
andswitch means for enabling either said first holding means2

or said second holding means in response to the status detection
signal.
2.

The sound volume control circuit according to claim 1,

further comprisingsetting means for selectively changing the first andsecond predetermined values of said firt and second holding meansin response to the status detection sigal.
3.

A sound volume control method comprising the steps of:holding a plurality of gaings corresponding to a pluralityof usage statuses of an apparatus;
detecting any of the plurality of usage statuses andoutputting a status detection signal; andselecting a corresponding one of the gains in response to
the status detection signal and amplifying an audio signal withthe selected gain.
4.

The sound volume control method according to claim 4,

further comprising the step ofchanging the plurality of gains manually.

問２．
The operation of the pulse detection circuit will now bedescribed.

When the clock pulse input to the input terminal CLK

is at the Vdd level, the P-channel FETT3 and T5 become
electrically discontinuous whereas the N-channel FETT4 and T6
become electrically continuous, so a voltage at the Vss level3

is therefore supplied to the both ends of the capacitor C2.

Whenthe clock pulse changes to the Vss level, the P-channel FETT3
becomes electrically continuous and a voltage at the Vdd levelis supplied to the one end of the capacitor C3.

At this time,

if the node D is at the Vss level, the substrate of the P-channel
FETT5 is at the level Vss.

The P-channel FETT5 cannot therefore

be turned on to function as a transistor.

However, since thepotential of the other end of the capacitor C3 increases as theone end thereof increases to the Vdd level, the PN junction formedby the substrate of the P-channel FETT5 and the region of theP-channel FETT5 connected to the capacitor C3 is biased in thenormal direction.

As a result, a current flows through the PN

junction and the capacitor C4 is charged with the current.
Increase in the potential of the node D due to the capacitor C4
being charged causes the P-channel FETT5 to function as atransistor and thereby to be turned on, making a current thatpasses through the capacitor C3 flow through the source-drain
pasage of the P-channel FETT5.

Further, at this time, theelectrode of the P-channel FETT5 that connects to the capacitor
C3 works as the source.

When the clock pulse is at the Vss level,

the P-channel FETT3 and T5 become electrically discontinuous andthe node D is therefore charged to a lower level than the Vddlevel.

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