JP3954989B2 - Speaker built-in telephone, PLL loop gain adjusting method, and program - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a howling countermeasure technique in a telephone with a speaker for providing a hands-free call function.
[0002]
[Prior art]
Conventionally, a telephone (hereinafter abbreviated as a speakerphone) that can make a call in a state where it is placed away from a user by acquiring transmitted voice from a microphone and emitting received voice from a built-in speaker at a suitable volume. Have been put to practical use.
Speakerphones are widely used because they accept the convenience of being able to talk without being held by the user's hand, that is, hands-free.
[0003]
The speaker of the speakerphone is generally provided separately from a receiver that is used in contact with the user's ear. This speaker emits a received voice with a volume much larger than that of the receiver, thereby giving mechanical vibration to the speakerphone housing.
The mechanical vibration caused by the received voice emitted from the speaker causes howling particularly in a speakerphone that wirelessly transmits and receives an audio signal using an analog modulation method.
[0004]
In such a speakerphone, (1) frequency modulation by the received voice is applied to the local signal of the radio unit by mechanical vibration, (2) the received voice component is mixed in the received signal via the local signal, and (3 ) Howling occurs by forming a positive feedback loop that is amplified and sounded again from the speaker.
The local signal is inherently generated stably by a PLL (Phase Locked Loop) controlled VCO (Voltage Controlled Oscillator) circuit, but under the influence of mechanical vibration, mechanical deformation that occurs in the capacitor of the VCO circuit ( Frequency modulation is applied due to (capacitance change).
[0005]
In order to reduce frequency modulation components and thereby increase howling resistance, measures may be taken to increase the PLL loop gain. By increasing the PLL loop gain, even when the frequency of the local signal fluctuates due to the influence of mechanical vibration, it is drawn to the original frequency at high speed and the frequency modulation component is reduced.
However, while this measure reduces the frequency modulation component, it causes a C / N (Carrier / Noise) ratio deterioration of the local signal. This is because speeding up the frequency change is synonymous with spreading the frequency spectrum of the local signal.
[0006]
This means that a technique for finding a suitable harmony point between the howling resistance and the C / N ratio (so-called trade-off) is required.
In general, there are other circuit characteristics that are incompatible with the PLL loop gain. For example, the relationship between the amount of output jitter caused by external noise input to the PLL loop and the followability of the PLL loop is one of them. Patent Document 1 discloses a technique for making a trade-off between them.
[0007]
In this document, (1) when the external noise is large, the output jitter amount is reduced by sacrificing the followability by lowering the PLL loop gain, and (2) when the external noise is small, the PLL loop A technique has been shown in which followability is improved in the range of an appropriate output jitter amount by increasing the gain.
[0008]
[Patent Document 1]
JP 2002-414406 A
[Problems to be solved by the invention]
However, the above prior art device adjusts the PLL loop gain according to the amount of external noise, so that it is possible to make a trade-off between the output jitter amount and the followability, but this is applied to the speakerphone. However, there is a problem that a trade-off between howling resistance and C / N ratio characteristics cannot be achieved.
[0010]
In view of the above problems, an object of the present invention is to provide a PLL loop gain adjustment method suitable as a countermeasure against howling of a speakerphone, and a speakerphone employing such an adjustment method.
[0011]
[Means for Solving the Problems]
(1) In order to solve the above problem, the telephone of the present invention is a telephone that has a built-in speaker for providing a hands-free call function and transmits and receives an audio signal using an analog modulation method, and generates a local signal. A PLL oscillating means capable of adjusting a loop gain, an accepting means for accepting an instruction to emit a received voice from the built-in speaker, and a loop gain of the PLL oscillating means when the instruction is accepted, And adjusting means for lowering the loop gain of the PLL oscillating means.
(2) The telephone further includes a determination unit that determines whether or not the volume of the received voice emitted from the built-in speaker is larger than a predetermined threshold value. The adjustment may be performed only when the determination is made, and in other cases, the loop gain of the PLL oscillation means may be lowered.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The telephone with a speaker according to an embodiment of the present invention is a dual mode that can be wirelessly connected to both a communication system that transmits and receives signals using an analog modulation method and a communication system that transmits and receives signals using a digital modulation method. Mobile phone.
[0013]
Then, the mobile phone includes a receiver that is used by placing it on the ear when holding a phone call, and a speaker that is used when calling in a hands-free manner. Talking in a hands-free manner is possible by emitting the received voice from the speaker.
Hereinafter, the mobile phone will be described in detail with reference to the drawings.
(appearance)
1A is a front view, FIG. 1B is a side view, and FIG. 1C is a rear view showing the appearance of a mobile phone 100 according to the present embodiment. In FIG. 1, characteristic components that are visible in appearance and that are related to the subject matter of the present invention are indicated by reference numerals.
[0014]
51 is a plurality of openings for emitting received voices emitted from the speakers, 52 is an opening for emitting received voices emitted from the receiver, 53 is an opening for receiving transmission voices to be acquired by the microphone, 60 is a display, 70 Is a plurality of operation keys including dial keys, off-hook keys, on-hook keys, etc., 71 is a speaker mode instruction key, and 72 is a volume key.
[0015]
The user can instruct the speaker mode to the cellular phone 100 by pressing the speaker mode instruction key 71 before or during the call.
When the speaker mode is instructed by the user, the cellular phone 100 causes the received voice to be emitted from the speaker at a suitable volume. For example, (1) Place the mobile phone on a desk and talk while operating a personal computer, and (2) Make a call while cooking with the mobile phone on the neck. The sound volume is such that the user can hear the received voice.
[0016]
In addition, the mobile phone 100 adjusts the volume of the received voice emitted by the speaker in accordance with the operation of the volume key 72 performed by the user according to the usage scene.
(overall structure)
FIG. 2 is a functional block diagram showing the overall configuration of the mobile phone 100. In FIG. 2, the same reference numerals are assigned to the components related to the components shown in FIG.
[0017]
As shown in the figure, the mobile phone 100 includes an antenna 10, a radio unit 20, a modem unit 30, a baseband unit 40, a speaker 51, a receiver 52, a microphone 53, a display unit 60, an operation unit 70, and a control unit 80. Composed.
Here, the baseband unit 40 is configured using a DSP (Digital Signal Processor) and a memory, and the DSP realizes its function by executing a program stored in the memory. Is configured using a CPU (Central Processing Unit) and a memory, and the function may be realized by the CPU executing a program stored in the memory.
[0018]
The display unit 60 is realized using a liquid crystal panel, an EL (Electro Luminescence) panel, a DMD (Digital Mirror Device), and the like, and the operation unit 70 is realized using a tact switch, a rotary switch, a membrane switch, or the like. Also good.
Hereinafter, the operation of each unit will be described for reception and transmission.
(Operation of each part during reception)
The radio unit 20 is provided in common for the digital system and the analog system.
[0019]
The RF reception signal received by the antenna 10 is guided to the low noise amplifier 12 via the duplexer 11 and amplified, and then frequency-converted by the mixer 13 into an IF reception signal in the IF band. The IF reception signal is output to the modem unit 30.
The RF local oscillator 16 generates an RF local signal by a PLL loop including a PLL control circuit 19 having a loop gain adjustment function, a low-pass filter 18 and a voltage controlled oscillation circuit 17. The generated RF local signal is supplied to the mixer 13 and the mixer 15 and used for frequency conversion performed by each.
[0020]
In response to the loop gain switching signal, the PLL control circuit 19 gives at least one of two types of loop gains, High and Low, to the PLL loop. As such a PLL control circuit, for example, a one-chip IC “MB15U30SP” manufactured by Fujitsu Limited can be used. The product has a function of adjusting the PLL loop gain by switching the charge pump current according to information given from the outside and held in the built-in register.
[0021]
How the controller 80 suitably issues the loop gain switching signal as a countermeasure against howling will be described in detail later.
The switch 21 supplies the IF reception signal input to the modulation / demodulation unit 30 to one of the digital demodulation unit 22 and the analog demodulation unit 23 indicated by the method switching signal.
[0022]
Here, the method switching signal is issued so as to indicate one of the analog modulation method and the digital modulation method, which is determined by the control unit 80 according to the wireless communication system. For this purpose, the control unit 80 holds in advance information (not shown) that associates each communication system that can be wirelessly connected with the modulation method to be used, and makes this determination with reference to the information. Issue a system switching signal.
[0023]
The communication system to be wirelessly connected may be selected according to the user's operation, or the communication system with the best radio wave condition may be automatically selected.
The IF reception signal digitally demodulated by the digital demodulation unit 22 and the IF reception signal analog-demodulated by the analog demodulation unit 23 are supplied to the down converter 26 via the low-pass filter 24 and the low-pass filter 25, respectively.
[0024]
In the down converter 26, the mixer 27 and the mixer 28 use the reception IF local signal supplied from the reception IF local oscillator 29 to convert the digitally demodulated IF reception signal and the analog demodulated IF reception signal, Each frequency is converted to a baseband and supplied to the baseband unit 40.
The baseband unit 40 D / A converts the digitally demodulated received signal into an analog signal and amplifies the received signal demodulated to the magnitude corresponding to the volume instruction signal, or directly accepts the analog demodulated received signal according to the volume instruction signal. Amplify to a certain size.
[0025]
If the speaker mode instruction signal is given, the baseband unit 40 causes the speaker 51 to sound the amplified reception signal, and also controls the speaker volume level signal indicating the actually received sound volume level. Output to 80. The received sound volume level is calculated, for example, by multiplying the maximum level of the received sound signal in a recent predetermined time by the value indicated by the sound volume instruction signal.
[0026]
If the speaker mode instruction signal is not given, the baseband unit 40 causes the receiver 52 to sound the amplified reception signal.
Here, the speaker mode instruction signal is issued from the control unit 80 after the speaker mode instruction key 71 is pressed until the speaker mode instruction key 71 is pressed again or until the call ends.
[0027]
Further, the volume instruction signal is issued from the control unit 80 in response to an operation performed on the volume key 72.
(Operation of each part during transmission)
The microphone 53 supplies an audio signal representing the acquired transmission voice to the baseband unit 40. The baseband unit 40 A / D converts the audio signal into a digital signal and amplifies and supplies the digital signal to the digital modulation unit 31 according to the method switching signal, or amplifies the audio signal as it is, and the analog modulation unit 32 To supply.
[0028]
The switch 33 outputs one of the audio signal digitally modulated by the digital modulator 31 and the audio signal analog-modulated by the analog modulator 32, which is instructed by the method switching signal, to the up-converter 34.
In the up-converter 34, the mixer 35 uses the transmission IF local signal supplied from the transmission IF local oscillator 36 to convert the digitally modulated audio signal or the analog modulated audio signal into an IF transmission signal in the IF band. Convert frequency. The preamplifier 37 amplifies the IF transmission signal and supplies it to the radio unit 20.
[0029]
The up-converter 34 and the preamplifier 37 are provided in common for the digital system and the analog system.
In the radio unit 20, the mixer 15 frequency-converts the IF transmission signal supplied from the modem unit 30 into an RF transmission signal in the radio band. The RF transmission signal is amplified by the high power amplifier 14 and then transmitted from the antenna 10 via the duplexer 11.
(PLL loop gain adjustment processing)
FIG. 3 is a flowchart showing a first adjustment process of the PLL loop gain performed by the control unit 80.
[0030]
The control unit 80 executes this process at least when a call is started and when the speaker mode instruction key 71 is operated.
The control unit 80 determines whether the modulation method indicated in the method switching signal is an analog method (S01). If the modulation method is an analog method, the control unit 80 determines whether a speaker mode instruction signal is issued (S02).
[0031]
When the speaker mode is instructed in an analog system, a loop gain switching signal for switching the loop gain to High is issued to the PLL control circuit 19 (S11). Otherwise, the loop gain is set to Low. A loop gain switching signal for switching is issued to the PLL control circuit 19 (S12).
FIG. 4 is a flowchart showing a second method of adjusting the PLL loop gain performed by the control unit 80.
[0032]
The control unit 80 executes this process at least when a call is started, when the speaker mode instruction key 71 is operated, and when the volume key 72 is operated.
The control unit 80 determines whether or not the modulation method indicated in the method switching signal is an analog method (S01). If the modulation method is an analog method, the controller 80 determines whether or not a speaker mode instruction signal is issued (S02). If the mode instruction signal has been issued, it is determined whether or not the received volume level indicated by the speaker volume level signal is greater than a predetermined threshold (S03).
[0033]
When the speaker mode is instructed in an analog manner and the received sound volume level is higher than a predetermined threshold value, a loop gain switching signal for switching the loop gain to High is issued to the PLL control circuit 19. (S11) In other cases, a loop gain switching signal for switching the loop gain to Low is issued to the PLL control circuit 19 (S12).
(Summary)
As described above, according to the first PLL loop gain adjustment method, the second PLL loop gain adjustment method, and the mobile phone 100 in which the PLL loop gain is adjusted based on these adjustment methods, howling occurs. Since the PLL loop gain is controlled according to the level of possibility, a trade-off between howling resistance and C / N ratio characteristics, which could not be achieved conventionally, can be realized.
[0034]
More specifically, according to the first PLL loop gain adjustment method, in the case of an analog modulation method with a high possibility of howling and the speaker mode, the C / N ratio is increased by setting the PLL loop gain to High. In a digital modulation scheme that increases howling tolerance at an acceptable level and has low possibility of occurrence of feedback, or when a receiver is made to sound the received voice, howling tolerance can be allowed by setting the PLL loop gain low. The trade-off of increasing the C / N ratio by weakening to a certain extent is realized.
[0035]
According to the second PLL loop gain adjustment method, the PLL loop gain is set low even when the possibility of occurrence of feedback is low and the received sound volume level is equal to or smaller than the threshold value. The scene where the trade-off with the / N ratio is realized can be expanded.
(Other variations)
Although the present invention has been described based on the above embodiment, it is needless to say that the present invention is not limited to the above embodiment. The following cases are also included in the present invention.
[0036]
The present invention may be a computer program for implementing the method described in the embodiment using a computer system, or may be a digital signal representing the program.
Further, the present invention may be a computer-readable recording medium in which the program or the digital signal is recorded, for example, a flexible disk, a hard disk, a CD, an MO, a DVD, a BD, a semiconductor memory, or the like.
[0037]
The present invention may be the computer program or the digital signal transmitted via an electric communication line, a wireless or wired communication line, a network represented by the Internet, or the like.
Further, the program or the digital signal may be recorded on the recording medium and transferred, or transferred via the network or the like, and executed in another independent computer system.
[0038]
【The invention's effect】
The telephone of the present invention is a telephone that includes a built-in speaker for providing a hands-free call function, transmits and receives an audio signal using an analog modulation method, and generates a local signal, and a PLL oscillation with adjustable loop gain Means, receiving means for receiving an instruction to emit received voice from the built-in speaker, and increasing the loop gain of the PLL oscillating means when the instruction is received, and increasing the loop gain of the PLL oscillating means in other cases. Adjusting means for lowering.
[0039]
According to this configuration, in the case of an analog modulation method with a high possibility of howling and sounding of the received voice in the built-in speaker, the C / N ratio is sacrificed to an acceptable level by increasing the PLL loop gain. There is a trade-off of increasing howling tolerance and lowering the possibility of occurrence of howling, and causing the receiver to pronounce the received voice, by lowering the PLL loop gain to weaken howling tolerance to an acceptable level and increasing the C / N ratio. Realized.
[0040]
The telephone further includes a determination unit that determines whether or not the volume of the received voice emitted from the built-in speaker is larger than a predetermined threshold value, and the adjustment unit makes a positive determination. The adjustment may be performed only in the case of a failure, and the loop gain of the PLL oscillation means may be lowered in other cases.
According to this configuration, when there is a low possibility of howling and the volume of the received voice is low, the PLL loop gain is kept low, so that a tradeoff between howling resistance and C / N ratio is realized. Can be expanded.
[0041]
The telephone is capable of transmitting and receiving an audio signal using any one of an analog modulation scheme and a digital modulation scheme, and further includes a determination unit that determines which one of the analog modulation scheme and the digital modulation scheme is used, The adjustment means may perform the adjustment only when the determination using the analog modulation method is made, and may lower the loop gain of the PLL oscillation means in other cases.
[0042]
According to this configuration, in the case of a digital modulation method in which the possibility of howling is low, the PLL loop gain is kept low, so that the scene where the trade-off between howling resistance and C / N ratio is realized can be expanded. .
The adjustment method of the present invention includes a built-in speaker for providing a hands-free call function, and PLL oscillation means capable of adjusting a loop gain for generating a local signal, and a telephone that transmits and receives an audio signal using an analog modulation method And a loop gain of the PLL oscillation means when a positive designation is accepted. And an adjustment step for reducing the loop gain of the PLL oscillation means in other cases.
[0043]
According to this configuration, the same effect as described above can be obtained.
The program according to the present invention includes a built-in speaker for providing a hands-free call function, PLL oscillation means capable of adjusting a loop gain for generating a local signal, and a control processor, and uses an analog modulation method for sound. A program for causing the processor to adjust the loop gain in a telephone that transmits and receives signals, and a reception step for receiving a designation as to whether or not a received voice is emitted from the built-in speaker, and a positive designation is accepted. If so, the processor is caused to execute an adjustment step of increasing the loop gain of the PLL oscillating means, and otherwise reducing the loop gain of the PLL oscillating means.
[0044]
According to this configuration, the same effect as described above can be obtained.
[Brief description of the drawings]
1A is a front view, FIG. 1B is a side view, and FIG.
FIG. 2 is a functional block diagram showing the overall configuration of the mobile phone 100. FIG.
FIG. 3 is a flowchart illustrating an example of a loop gain control process.
FIG. 4 is a flowchart illustrating another example of the loop gain control process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Antenna 11 Duplexer 12 Low noise amplifier 13 Mixer 14 High power amplifier 15 Mixer 16 RF local oscillator 17 Voltage control oscillation circuit 18 Low pass filter 19 PLL control circuit 20 Radio part 21 Switch 22 Digital demodulator 23 Analog demodulator 24, 25 Low pass filter 26 Downconverters 27 and 28 Mixer 29 Reception IF station generator 30 Modulator / demodulator 31 Digital modulator 32 Analog modulator 33 Switch 34 Upconverter 35 Mixer 36 IF station transmitter 37 Transmitter 37 Preamplifier 40 Baseband unit 51 Speaker 52 Receiver 53 Microphone 60 Display unit 70 Operation unit 71 Speaker mode instruction key 72 Volume key 80 Control unit 100 Mobile phone

Claims (5)

A telephone having a built-in speaker for providing a hands-free call function and transmitting and receiving an audio signal using an analog modulation method,
PLL oscillation means for generating a local signal and adjustable loop gain;
Accepting means for accepting an instruction to emit a received voice from the built-in speaker;
A telephone comprising: adjusting means for increasing a loop gain of the PLL oscillating means when the instruction is accepted, and reducing a loop gain of the PLL oscillating means in other cases. The telephone further includes:
Determining means for determining whether or not the volume of the received voice emitted from the built-in speaker is greater than a predetermined threshold;
2. The telephone set according to claim 1, wherein the adjustment unit performs the adjustment only when a positive determination is made, and reduces the loop gain of the PLL oscillation unit in other cases. The telephone is capable of transmitting and receiving audio signals using either an analog modulation scheme or a digital modulation scheme, and
A decision means for deciding whether to use an analog modulation scheme or a digital modulation scheme;
2. The telephone set according to claim 1, wherein the adjustment unit performs the adjustment only when a decision to use an analog modulation method is made, and reduces the loop gain of the PLL oscillation unit in other cases. The loop gain used in a telephone having a built-in speaker for providing a hands-free call function and a PLL oscillation means capable of adjusting a loop gain for generating a local signal and transmitting / receiving an audio signal using an analog modulation method Adjustment method,
An accepting step for accepting designation as to whether or not the received voice is emitted from the built-in speaker;
An adjustment step of increasing the loop gain of the PLL oscillating means when a positive designation is accepted, and lowering the loop gain of the PLL oscillating means in other cases. In a telephone having a built-in speaker for providing a hands-free calling function, a PLL oscillation means capable of adjusting a loop gain for generating a local signal, and a control processor, and transmitting and receiving an audio signal using an analog modulation method , A program for causing the processor to adjust the loop gain,
An accepting step for accepting designation as to whether or not the received voice is emitted from the built-in speaker;
A program for causing the processor to execute an adjustment step of increasing the loop gain of the PLL oscillating means when a positive designation is accepted, and lowering the loop gain of the PLL oscillating means in other cases.

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