JPH10126163A - Radio equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the radio equipment by which output of a noise sound is prevented, even when no mute function is in operation immediately after application of power. SOLUTION: On the premises of the radio equipment provided with a power amplifier 1 for sound signal amplification and a speaker 4 providing an output of the amplifier externally, a switching controller 3 that is turned off for a prescribed period after the application of power is provided in series between the amplifier 1 and the speaker 4. The switching controller 3 is provided with an FET 7, a control section 8 that controls conduction/nonconduction of the FET 7, and a latch section 9 that latches the on state when the FET 7 is conductive. The latch means 9 is provided with a capacitor C1 for DC component cut-off between the FET 7 and the speaker 4, and a voltage between the capacitor C1 and the speaker 4 is fed to a gate of the FET 7. Then the gate voltage is lower by a DC component voltage portion from the voltage applied to its source, so that the gate voltage is always kept low and the FET 7 maintains the conductive state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless device, and more particularly, to a wireless device to which a device for preventing noise generated at power-on or the like from being output as sound is added.

[0002]

2. Description of the Related Art In a radio, a battery or the like is used as a power supply. Various electric circuits inside the wireless device are driven by power supply from a single power supply composed of such a battery. And to drive the speaker, for example, directly connect the output of the power amplifier to the speaker,
Outputs audio. Furthermore, during use, various kinds of noises and the like may be generated, and if the noises are transmitted to the speakers as they are, annoying noise sounds may be output, which may cause discomfort to the user. In view of the above, a usual wireless device is provided with a mute function of turning off the speaker output when noise generation is detected on the CPU side mounted on the wireless device to improve the usability.

[0003]

In order to operate the above-mentioned mute function, it is necessary that the CPU and the like operate normally. In a transition period immediately after the power is turned on, a certain time lag occurs until a power supply voltage for operating the CPU is supplied. On the other hand, the speaker is ready for audio output immediately after the power is turned on (before the CPU starts normal operation).

As a result, when noise is generated from the power amplifier when the power is turned on, the mute function of the CPU does not work, and the noise (abnormal sound) is output via a speaker, giving a user discomfort. There is a risk that it will.

Conventionally, a power switch, such as a rotary switch or a toggle switch, which generates a click sound when the switch is switched and which can be reliably turned on at one time, has been used. Then, only one noise is generated when the power is turned on, and at the same time, a clicking sound is also generated.

However, recent switches use a feather-touch push type switch. Such a switch supplies power to a circuit while the switch is being depressed, the circuit itself holds power, and after the switch is released. The power supply is also turned on, so if the switch is repeatedly turned on and off due to unstable operation, the power-on noise is continuously generated and there is no click sound. In some cases, such noises are conspicuous, resulting in unpleasant sounds for the user, and a feeling of use may be reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and an object of the present invention is to solve the above-described problem and to reduce noise noise even when the mute function is not activated immediately after power-on. Output can be suppressed, the user does not hear unpleasant sounds, the usability and usability are improved, and the effect can be realized with a simple configuration. It is an object of the present invention to provide a wireless device capable of reliably transmitting the output of the amplifier to the audio output means side (when the mute function does not work) in a normal use situation.

[0008]

In order to achieve the above-mentioned object, a wireless device according to the present invention comprises a wireless amplifier comprising an amplifier for amplifying an audio signal and audio output means for outputting the output of the amplifier to the outside. As a premise, a switching control device was provided in series between the amplifier and the audio output means. The switching control device is opened for a predetermined period immediately after the power is turned on, and cuts off transmission from the output of the amplifier to the audio output means (claim 1).

Here, the predetermined period may be a fixed time measured by a timer, for example.
As described in the above, the variable time according to the operation state of the wireless device may be set such that the mute function becomes operable. The audio output means includes not only a device that directly outputs audio such as a speaker, but also a terminal that outputs a finally audible signal such as an earphone jack.

With this configuration, since the switching control device is in the open state for a certain period after the power is turned on, the signal line for audio output is physically cut off. Even if noise occurs, an unpleasant sound based on the noise is not output to the outside. Therefore, the user is less likely to hear harsh sounds as much as possible, resulting in an easy-to-use wireless device.

As an example of a specific configuration of the switching control device, for example, an FET interposed between the output of the amplifier and the audio output means, and a control means for controlling ON / OFF of the FET are provided. Holding means for holding the ON state when the FET is turned on by the control means. At this time, as the holding means,
A DC component cutting capacitor is provided between the FET and the audio output means, and a voltage at an arbitrary position between the capacitor and the audio output means is applied as a gate voltage of the FET. Item 2).

That is, the FET is on (the switch is closed)
To maintain the state, the gate voltage needs to be lower than the voltage applied to the source of the FET.
And since the voltage applied to it is an audio signal,
Since the voltage swings from the power supply voltage to the ground (0V) level, the instantaneous value may be around 0V. In this case, it is necessary to apply a negative bias to the gate voltage in order to keep the FET on. On the other hand, in the case of a portable wireless device, it is necessary to reduce the size and weight, and the power supply battery is a factor that hinders the reduction in size and weight. It cannot be put to practical use. In addition, it is necessary to reduce the size and weight of the installation-type wireless device, and separately providing a power supply for maintaining the ON state of the FET results in an increase in the number of components, which negates miniaturization.

Therefore, in the present invention, since a capacitor for cutting a DC component is provided on the drain side of the FET, an AC signal (same as a signal given to the source side) appearing on the drain side needs to be swung on the plus side. , And a certain DC component is superimposed, and the DC component is removed by passing through a capacitor. Then, the obtained signal is a signal that oscillates with respect to the ground, with the superposed DC component removed from the AC signal on the source side. Moreover, the two signals (the signals before and after the removal of the DC component) are synchronized, and there is a potential difference between the DC components. As a result, the gate voltage of the FET is always lower than the voltage applied to the source by the potential difference of the DC component (if the signal applied to the source is close to 0 V, the gate voltage will be negative). The FET keeps on regardless of the level of the instantaneous value of the signal applied to the source.

Moreover, since the voltage applied to the gate of the FET is generated based on the signal output from the drain, there is no need to provide a separate negative bias power supply, and it is necessary to drive a normal electric circuit. A single power supply. Therefore, the device does not increase in size and does not increase much in weight.

Note that the DC component cutting capacitor is:
Although it may be provided for the device of the present invention, the capacitor for cutting the DC component is usually mounted immediately before the speaker, so that the capacitor for the speaker and the gate bias for generating the gate bias of the FET of the present invention are provided. Of course, a capacitor may be used.

As the control means, various structures can be used as long as the FET is turned off (the switch is opened) when the power is turned on and turned on after a lapse of a predetermined time. As shown, it can be composed of transistors connected in two stages. That is, it includes a first transistor (Q1) connected to a gate and controlling conduction / opening of a power supply voltage, and a second transistor (Q2) controlling a gate voltage of the first transistor. When the power is turned on, the second transistor is turned on by applying a voltage based on the power supply voltage to the base, and is turned off by the base falling to the ground based on a control signal issued under certain conditions after the power is turned on. (Claim 3). As a result of the experiment, it was confirmed that such a configuration operates most stably. This configuration is described in detail in the embodiment.

Further, the control signal defined in claim 3 is generated by detecting that the mute function mounted on the wireless device has become operable (in the embodiment, generated by the CPU). (Claim 4). With this configuration, before the mute function operates normally, the opening / closing control device is open and reliably shuts off audio output from the amplifier side. The control device closes to enable audio output. If noise or the like subsequently occurs, the original mute function is exerted and the mute is applied, so that noise is not output as sound. By doing so, after the mute function operates normally, audio output can be performed without delay, and the dead time during which audio output cannot be performed can be shortened as much as possible.

In the above-described various configurations, the above-described F
Connect a bypass resistor between the source and drain of ET,
When the FET is off, a minute current may flow through the bypass resistor. This allows the capacitor to be charged via the bypass resistor even when the FET is turned off immediately after the power is turned on, so that when the FET is turned on, inrush current flows through the capacitor and noise can be generated. As much as possible. And
After the FET is turned on, it flows on the side of the FET having a small resistance, so that there is almost no loss due to the provision of the bypass resistor.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an audio output signal (AF) is input to a power amplifier 1 and a signal amplified there is passed through an opening / closing control device 3 which is an essential part of the present invention. To the speaker 4 for audio output. In addition, a jack 5 for an earphone is provided in parallel with the speaker 4. The power amplifier 1 is supplied with a power supply voltage VDD. The power supply voltage VDD is supplied from a battery (not shown) since this embodiment shows an example applied to a portable wireless device. In this example, it is set so that 4.8 V is applied.

Here, in the present invention, the output of the power amplifier 1 was directly connected to the speaker 4 (there was a capacitor C1 for removing a DC component), but the signal line as described above One of the features is that the opening / closing control device 3 is inserted and arranged in series. Then, by a control mechanism described later, the opening / closing control device 3 is in an open state for a certain period from the time of turning on the power (immediately after), and the transmission of the output of the power amplifier 1 to the speaker 4 is stopped. The power amplifier 1 is closed so that the output of the power amplifier 1 is output via the speaker 4.

Next, a specific configuration of the switching control device 3 will be described. First, the source S of the FET 7 is connected to the output (signal line) of the power amplifier 1, and the drain D of the FET 7 is connected to the capacitor C1 for removing a DC component. This FET 7 is a voltage control and functions as an open / close switch. That is, as is well known, when a predetermined voltage is applied to the gate G of the FET 7 to turn on the FET 7, a short circuit occurs between the source and the drain, and the switch functions to close. Then, the switching control device 3 includes the FET 7,
A control unit 8 for controlling on / off of the FET 7;
After the switch is turned on (the switch is closed), the holding unit 9 holds the state.

The control unit 8 includes two-stage transistors Q1, Q
2 is provided. That is, the first transistor Q1 is
The first transistor Q1 is connected to the gate of T7 to control on / off of the first transistor Q1, thereby giving a direct on / off command to the FET7. The on / off of the first transistor Q1 is controlled by the second transistor Q2.

That is, the power supply voltage VDD is applied to the resistors R1 and R2 connected in series, and
The base of the second transistor Q2 is connected to the connection between 1 and R2. Thus, a voltage divided based on the two resistors R1 and R2 is applied to the base of the second transistor Q2. Further, a control signal from a CPU (not shown) is also supplied to the base of the second transistor Q2. More specifically, the terminal 10 is set to be High (open state) until a certain time has elapsed since the power-on, and the terminal 10 is set to be Low (fall to ground) after the certain time has elapsed. Also, the second
When the transistor Q2 is on, the first transistor Q1
The resistor R3 connected in series with the voltage voltage VDD
The voltage divided by R4 is applied to turn on.

On the other hand, the holding section 9 includes a capacitor C1 and a resistor R5 having one end connected to the branch point of the capacitor C1 and the speaker 3. The other end of the resistor R5 has
It is connected to the gate of FET7. As a result, the voltage from which the DC component has been removed by the capacitor C1 is applied to the FET.
7 is applied to the gate.

Further, in this embodiment, a bypass resistor R6 is connected between the source and the drain of the FET 7. The bypass resistor R6 has a high resistance, so that a small current flows through the bypass resistor R6 when the FET 7 is off.

Next, the operation principle of the above example will be described. First, when the power is off, each transistor Q
1, Q2 and the FET 7 are turned off, and the terminal 10 connected to the base of the second transistor Q2 is also open. When the power is turned on in this state, the power supply voltage VDD gradually increases, but initially does not reach a voltage sufficient to drive the CPU. At this time, first, the voltage divided by the resistors R1 and R2 is applied to the base of the second transistor Q2 to turn on. Then, since the resistor R3 is connected to the ground, a voltage divided by the resistance ratio also appears at the connection point of the resistors R3 and R4 connected in series to the power supply voltage VDD, and the voltage causes the first transistor to be turned on. Q1 is also turned on. Then, FE is input via the first transistor Q1.
The gate of T7 will be directly connected to the power supply voltage,
The gate voltage of 7 becomes the power supply voltage. Therefore, since the voltage becomes higher than the voltage on the source side, when the FET is turned off, the switch is opened. Then, both transistors Q1,
Since Q2 is turned on immediately after the power is turned on, the FET 7 is also turned off immediately after the power is turned on, and the signal output from the power amplifier 1 is cut off.

When a certain period of time elapses and the CPU becomes operable (the mute function is exhibited), a control signal is issued from the CPU, and the terminal 10 is short-circuited (falls to ground). Then, the base of the second transistor Q2 falls to ground, so that the base voltage becomes 0 and the second transistor Q2 is turned off. Then, the resistor R3 enters an oven state, so that the base voltage of the first transistor Q1 becomes the power supply voltage and turns off. As a result, the gate of the FET 7 is disconnected from the power supply voltage VDD, and the terminal voltage (after removing the DC component) of the capacitor C1 is applied.

Then, the source of the FET becomes higher in potential than the gate, and the FET 7 is turned on. As a result, the output of the power amplifier 1 is transmitted to the speaker 4 and the jack 5, and the audio output becomes possible.

On the other hand, the input (point A) and the output (B) of the opening / closing control device 3 when the FET 7 becomes conductive as described above.
The correlation between the signal waveforms (point) is as shown in FIG. That is, the input (point A) of the switching control device 3 is offset by superimposing a DC component by a predetermined voltage (for example, 2 V) as shown in FIG. The output (point B) at this time has a waveform oscillating around 0 V because the DC component is removed by the capacitor C1, as shown in FIG. As is clear from the comparison between the two, since the reference position is merely converted from 2 V to 0 V, the two are synchronized, and at any time (t1, t2, t3, t4,...) The potential difference between the instantaneous values of the parents is 2V.

Therefore, the voltage based on FIG. 7B is applied to the gate of the FET 7 (slight loss due to the resistor R5), so that the potential difference from the source of the FET 7 is always about 2
Since the value is lower by V, the on state is maintained.

Further, in this embodiment, since the bypass resistor R6 is provided, even when the FET 7 is turned off when the power is turned on, a very small current flows through the bypass resistor R6, so that the capacitor C1 is charged. Therefore, when the FET 7 is turned on, the capacitor C1 has been charged or has been charged to some extent, so that an inrush current does not occur and no noise is generated due to the inrush current.

In the above-described embodiment, the control section 8 is composed of two-stage transistors. However, the present invention is not limited to this.
A control signal from the PU may be applied to the base of the transistor Q1. Further, in the present invention, the transistor is turned off based on the control signal from the CPU, and thereby the FET is turned on. However, the present invention is not limited to this. The transistor may be turned off after the lapse of time, and various modifications are possible. Further, it goes without saying that the bypass resistor R6 is not necessarily provided. Further, in the above-described embodiment, the portable wireless device has been described. However, the present embodiment is not limited to this and can be applied to an installation type wireless device.

[0033]

As described above, in the radio according to the present invention,
At the beginning of power-on, the open / close control device is in the open state, and the path for physically sending the amplifier output to the audio output means is shut off, so noise is output even immediately after power-on, even when the mute function is not operating. Can be suppressed, and the user does not hear harsh sounds, so that usability and feeling of use are improved. In addition, since the opening / closing control device is closed after a certain period of time, the output of the amplifier can be reliably transmitted to the audio output means side (when the mute function does not work) under normal use conditions.

In addition, by using an FET as a switch for opening and closing as described in claim 2, the gate voltage during normal use is determined based on the terminal voltage of the DC cut capacitor, so that no special power supply is required. The FET can be kept on. Therefore, it can be realized with a simple configuration and does not hinder downsizing and weight reduction.

Further, according to the fifth aspect, when the switching control device is switched to the closed state, it is possible to suppress the generation of noise based on the rush current to the capacitor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a main part of the present invention.

FIG. 2 is a diagram illustrating the operation of a holding unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power amplifier 3 Opening / closing control device 4 Speaker (sound output means) 5 Jack (sound output means) 7 FET 8 Control part 9 Holding part 10 Terminal (a control signal is given) C1 Capacitor Q1 First transistor Q2 Second transistor R6 Bypass resistance

Claims (5)

[Claims] 1. A radio device comprising an amplifier for amplifying an audio signal and audio output means for outputting the output of the amplifier to the outside, wherein a switching control device is provided in series between the amplifier and the audio output means. A radio device, wherein the opening / closing control device is opened for a predetermined period immediately after power-on to interrupt transmission from the output of the amplifier to the audio output means. 2. The control device according to claim 1, wherein the switching control device includes an FET interposed between the output of the amplifier and the audio output unit, a control device for controlling on / off of the FET, and an FET turned on by the control device. And a holding means for holding the ON state when the power supply is turned on, the holding means providing a DC component cutting capacitor between the FET and the audio output means, and the capacitor and the audio output means. 2. The wireless device according to claim 1, wherein a voltage at an arbitrary position between the two is applied as a gate voltage of the FET. 3. A first transistor (Q1) connected to a gate of the FET and controlling conduction / opening of a power supply voltage, and a second transistor (Q1) controlling a gate voltage of the first transistor. When the power is turned on, the second transistor is turned on by applying a voltage based on the power supply voltage to the base, and the base is grounded based on a control signal issued under certain conditions after the power is turned on. The wireless device according to claim 1, wherein the wireless device is turned off when dropped. 4. The wireless device according to claim 3, wherein the control signal is generated by detecting that a mute function mounted on the wireless device has become operable. 5. The device according to claim 2, wherein a bypass resistor is connected between the source and the drain of the FET, and a small current flows through the bypass resistor when the FET is off. The wireless device according to any one of the preceding claims.