JPS6253557A - Acoustic coupler - Google Patents

Abstract

PURPOSE:To improve S/N over a wide band by applying 1/2 frequency division to an output AC signal of a modulation circuit of a speaker inputting an acoustic signal and driving the speaker with a call signal superimposed with a DC component to reduce the distortion of an output signal from a carbon microphone. CONSTITUTION:A transmission section 14 consists of a modulation circuit 2, a frequency division circuit 3 converting the modulated AC signal into a half frequency, a low-pass filter 4, an amplifier 5, a DC superimposing circuit 6 superimposing a DC on the AC signal, a speaker 7 inputting the acoustic signal to a telephone set transmission microphone and a control section 8 adjusting the timing of data transmission. A DC voltage in matching with the condition of Reo/delta=xAC.xDC is superimposed in the AC signal being the result of frequency division to an output signal of the modulation circuit 2 in the DC superimposing circuit 6 and the speaker 7 is driven, then the output current of the telephone set transmission carbon microphone does not include the 2nd harmonic having the frequency equal to the carrier to reduce the deterioration in S/N in the conversion system of the carbon microphone.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a telephone set and an acoustic coupling device for transmitting various data using a telephone line. It had the configuration shown in Figure 4. That is, the digital signal outputted from the data terminal device 31 is converted into a voice band frequency signal by frequency,
A modulation circuit 32 that performs amplitude two-phase modulation. The high-frequency components of the modulated AC signal are attenuated. A low-pass filter 33, a speaker 35 that converts an alternating current signal into an acoustic signal to be input to the transmitting microphone of the telephone, an amplifier 34 for driving the speaker 36, and a data terminal device 31
A control unit 3 that adjusts the timing of data transmission between
6, a microphone 37 that receives the acoustic signal from the telephone receiver speaker, a low-pass filter 38 for reducing noise in the transmission system, an amplifier 39 that amplifies the received signal, and a demodulator that demodulates the received signal into a digital signal. An acoustic coupling device is constituted by the circuit 40 and a receiving section 43 consisting of a carrier detector section 41 that transmits an incoming carrier signal to the data terminal 31.

Problems to be Solved by the Invention However, with the above-described configuration of the acoustic coupling device, the output frequency characteristics of the transmitting microphone of the telephone set vary with respect to the level of the total output frequency characteristics 63, as shown in FIG. , the level of the second harmonic component 54 is 15 dB to 18 d
A highly distorted waveform of B is being transmitted. This is because a carbon microphone is used as a transmitting microphone, and the acoustoelectric conversion output of the carbon microphone has the relationship shown in equation (1). R: Static resistance e of carbon microphone.

δ: Specific resistance of carbon particles x*sinθJt: Displacement of electrode due to acoustic signal cos2
The waveform has a term (second harmonic) added to ω,
This is because the carbon microphone generates and transmits an AC output current waveform 52 in response to an acoustic input waveform 51, as shown in FIG. Therefore, when using a carrier with a very narrow band, it is possible to attenuate the distortion component with a low-pass filter and demodulate it, but when using a wide band signal such as a DTMF signal or an analog image signal, the distortion becomes a noise component. Therefore, the S/H deteriorates significantly, making it difficult to demodulate into a desired digital signal.

Therefore, the present invention provides an acoustic coupling device that reduces distortion of an output signal from a carbon microphone and improves S/N over a wide band.

Means for Solving the Problem In order to solve this problem, the present invention divides the output AC signal of the modulation circuit into 1/2 and divides the frequency of the output AC signal of the modulation circuit into 1/2 for the speaker that inputs the acoustic signal to the transmitting microphone of the telephone, and further divides the frequency of the output AC signal into DC. It is driven by a transmission signal with a DC component superimposed on the output AC signal of the modulation circuit, or it is driven with a transmission signal in which a DC component is superimposed on the output AC signal of the modulation circuit, and then the double frequency of this transmission signal is detected as a carrier.
The configuration is such that demodulation is performed.

Effect With the above configuration, the output sound pressure P of the speaker driven by the transmission signal obtained by superimposing the DC component on the output AC signal of the modulation circuit is P = Ppc + PAcCosωt −・
-・- (2) PDc: Asymmetric component of sound pressure due to DC component PAc: Sound pressure component due to AC signal, and the electrode of the carbon microphone has a displacement I that is proportional to this sound pressure P. X = X DC + X ACCOBωt
-.=(3) xDc: Displacement due to PDc xAc: Displacement due to PAc is generated. At that time, the current output of the carbon microphone is expressed as I, and if we consider up to the second harmonic of the current, we get: eo/B = xDc ``The DC component that satisfies the AC conditions is superimposed. If it is assumed that
This becomes a sine wave with twice the frequency of the input signal, greatly reducing distortion and improving the S/N of the transmission signal.

EXAMPLE An acoustic coupling device according to an example of the present invention will be described below.

As shown in FIG. 1, a digital signal output from a data terminal device 1 modulates an AC signal at a voice band frequency. A modulation circuit 2, a frequency dividing circuit 3 that converts the modulated AC signal into a three-tone wave number, a low-pass filter 4 that attenuates the high-frequency components of the frequency-divided AC signal, and amplifies the frequency-divided AC signal. An amplifier 6, a DC superimposition circuit 6 that superimposes a DC signal on an AC signal, a speaker 7 that inputs an acoustic signal to a telephone transmission microphone, and a control unit 8 that adjusts the timing of data transmission with the data terminal device 1. a transmitting section 14, a microphone 9 that receives an acoustic signal from an electric receiver speaker, a low-pass filter 10 for reducing noise in the transmission system, and an amplifier 1 for amplifying the received signal.
1. Demodulation circuit 12 that demodulates the received signal into a digital signal;
Further, a receiving section 15 comprising a carrier detector 13 that transmits the arrival of a carrier signal to the data terminal device 1 constitutes an acoustic coupling device.

In the DC superimposition circuit 6, Bo0/δ=xAC' ”D
When a DC voltage that satisfies the condition C is superimposed on an AC signal obtained by frequency-dividing the output signal (carrier) of the modulation circuit 2 and the speaker 7 is driven, the output current of the telephone transmitting carbon microphone is expressed by the above equation (6). As shown in FIG. 2, a signal that does not contain the second harmonic having the same frequency as the carrier is transmitted, and the deterioration in S/N in the conversion system of the carbon microphone can be extremely reduced.

Similarly, when a direct current is superimposed on the carrier from the modulation circuit 2 so that the telephone transmitting output has a waveform with less distortion and twice the frequency of the carrier, and a frequency dividing circuit is provided in the receiving section 15, the S/ Deterioration of N can be prevented.

Effects of the Invention As described above, the present invention greatly reduces the distortion generated in the conversion system of the carbon microphone by superimposing a DC component on the output signal of the modulation circuit to drive the speaker, thereby improving the S/
High N transmission can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an acoustic coupling device according to an embodiment of the present invention, FIG. 2 is a transmission waveform diagram of an embodiment of the present invention, and FIG. 3 is a block diagram of a conventional acoustic coupling device.
Fig. 4 is a transmission waveform diagram in a conventional configuration, and Fig. 5 is a transmission level frequency characteristic and harmonic distortion characteristic diagram in the conventional configuration.
...Modulation circuit, 3...Divide circuit, 4...
...Low pass filter, 5...Amplifier, 6...
...DC superimposition circuit, 7... Speaker, 8.
...Control unit, 9...Microphone, 1Q
......Low pass filter, 11...Amplifier, 12...Demodulation circuit, 13...Carrier detector, 14...Transmission section, 15.・・・
...Receiving section. Name of agent: Patent attorney Toshio Nakao and 1 other person7-
Figure 2 Figure 3 Figure 4 Figure 5

Claims (2)

[Claims] (1) It has a speaker that inputs an acoustic signal to the transmitting microphone of the telephone, and this speaker is driven by a transmission signal obtained by dividing the output AC signal frequency of the modulation circuit by 1/2 and further superimposing a DC component. An acoustic coupling device characterized by: (2) A speaker that inputs an acoustic signal to the transmitting microphone of the telephone is driven by a transmission signal in which a DC component is superimposed on the output AC signal of the modulation circuit, and
An acoustic coupling device characterized by detecting and demodulating double frequencies as carriers.