JPS627740B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a periodic tone signal detection circuit for receiving in a wireless communication receiver.

In mobile wireless communication systems, when a periodic tone signal is transmitted via a wireless line, it is affected by fading and causes DC fluctuations in the demodulated output of the receiver, making it impossible to detect the signal. . Generally, when a wireless line is used, fluctuations in electric field strength due to temporal changes in the medium, that is, fading, occur, resulting in variations in the strength of the received signal at the receiver. When the received signal level becomes weak, the receiver's FM wave and PM wave demodulating circuit demodulates noise that matches the center frequency, and the DC voltage component of that noise is superimposed on the weak tone signal as the DC component of the demodulated output. appear. Conversely, when the received signal level becomes stronger, a DC voltage component corresponding to the center frequency of the received wave appears as a demodulated output superimposed on the strong tone signal. In this way, when the DC voltage component of the demodulated output fluctuates in response to fluctuations in the level of the received wave, the level of the tone signal changes accordingly. Therefore, in order to detect the tone signal, a simple rectangle is installed after the demodulation circuit. Even if a wave shaping circuit or a comparison circuit operating with a threshold value is provided, it is not possible to continuously detect an error-free tone signal. As a conventional method to prevent this, a method has been adopted in which a time diversity effect is utilized using an analog delay element to compensate for a portion of the periodic signal lost due to fading. However, in such conventional methods, analog delay elements are expensive;
Disadvantages include that the delay amount of the analog delay element is fixed in time, and that the periodic signal to be transmitted cannot be freely changed from a low frequency to a high frequency.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional art by using a simple configuration consisting of only a differentiating circuit, an integrating circuit, and a comparing circuit to correctly process periodic signals of arbitrary frequencies without being affected by fading. An object of the present invention is to provide a tone signal detection circuit in a wireless communication receiver capable of detecting a tone signal.

According to the present invention, a differentiating circuit receives a periodic tone signal obtained through a demodulation circuit and differentiates the tone signal; an integrating circuit also receives the tone signal and integrates the tone signal; A tone signal detection circuit in a wireless communication receiver is provided, comprising a comparison circuit that compares the output of the differentiating circuit and the output of the integrating circuit, and detecting the periodic tone signal from the comparison circuit. .

Here, in order to facilitate comparison with the present invention,
An example of the configuration of a conventional signal detection circuit will be described with reference to FIG. In the figure, 1 is a demodulation circuit, 2 is an analog delay circuit, 3 is a differential amplifier circuit, and 4 is a comparison circuit. If the period of the input signal demodulated by the demodulation circuit 1 is T, then the analog delay circuit 2 is set to delay the signal by (2n-1)T/2 (n is an integer). The circuit 2-1 in the analog delay circuit 2 is an analog delay element, for example,
BBD (Backet Brigade Device), CCD (Charge
Coupled Device) etc. are used. Circuit 2-2
is a high speed clock signal generation circuit for operating the analog delay element 2-1. Even if the DC voltage at the output of the demodulation circuit 1 increases due to fading, if the output of the analog delay circuit 2 is stable, a normal rectangular pulse can be obtained at the output of the comparison circuit 4. However, BBD in analog delay circuit 2,
Or when using a delay element such as a CCD,
A high-speed clock oscillation circuit is required, making it economically expensive. Additionally, since the delay time of the analog delay element 2-1 is determined by the oscillation frequency of the high-speed clock signal generation circuit 2-2, only one type of periodic signal with a specific frequency can be used as the periodic signal that can be transmitted. Can not. Therefore, in order to eliminate this drawback, it may be possible to use an analog phase circuit with a 180 degree phase shift made up of components such as resistors and capacitors in place of the analog delay circuit 2, but in that case, the phase circuit 1 of the parts used
Each of these factors is directly related to variations in the phase amount, resulting in a defect that stable operation cannot be performed for periodic tone signals in a wide frequency band, including variations in temperature characteristics.

Next, embodiments of the signal detection circuit according to the present invention will be described with reference to the drawings.

FIG. 2 shows the configuration of a first embodiment according to the present invention. In this example, 11 is a demodulation circuit, 12 is a differentiating circuit consisting of a capacitor 12-1 and a resistor 12-2, and 13 is an integrating circuit consisting of a resistor 13-1 and a capacitor 13-2. Differential circuit 1
2 and the outputs of the integrating circuit 13 are compared in a comparing circuit 14. Now, assuming that the frequency of the tone signal is ω=2π, the transfer function of the differentiating circuit 12 is jωC ₁₂ R ₁₂ /(1+jω
C ₁₂ R ₁₂ ), and the transfer function of the integrating circuit 13 is 1/(1+jωC ₁₃ R ₁₃ ). Here, C ₁₂ ,
C ₁₃ represents the capacitance of the capacitors 12-1 and 13-2, respectively, and R ₁₂ and R ₁₃ represent the resistance values of the capacitors 12-2 and 13-1, respectively. Therefore, 1≫ωC ₁₂ R ₁₂ , 1≪ω
If C ₁₃ R ₁₃ is satisfied, capacitor 12-1,
Even if the values of 13-2 and resistors 12-2 and 13-1 vary considerably, the output b of the differentiating circuit 12 will have a phase advance of exactly π/2, and the output c of the integrating circuit 13 will have a phase advance of π/2. is delayed. Or, 1≫ω
It can be seen that for all periodic tone signals with frequencies that satisfy C ₁₂ R ₁₂ , 1≪ωC ₁₃ R ₁₃ , the output signals b and c have a relationship that is accurately shifted by π/2 from the input signal a. . FIG. 3, which shows the operating waveforms of these signals, shows the case where the DC fluctuation value of the demodulated output a changes to V. The output b of the differentiating circuit leads the demodulated output a by π/2, and the output c of the integrating circuit 13 lags behind the demodulated output a by π/2. When the outputs b and c are compared by the comparator circuit 14, the detection pulse d is accurately obtained as a tone signal on the output side regardless of fluctuations in the DC component. In addition, in this example, the tone signal is a simple repeating code indicating that a call has been received, but this can be used as a receiver identification signal by a combination of "1" and "0", It has already been known that it can be used for other purposes.

FIG. 4 shows the configuration of a second embodiment according to the present invention. In this figure as well, 21,2
2, 23 and 24 indicate a demodulation circuit, a differentiation circuit, an integration circuit and a comparison circuit, respectively. However, the difference from the first embodiment in FIG. 3 is that the elements constituting the differentiating circuit 22 and the integrating circuit 23 use resistors 22-1, 23-2 and coils 22-2, 23-1, respectively. point, and the rest have exactly the same configuration. In this example, the transfer function of the differentiating circuit 22 is jωL ₂₂ /(R ₂₂ +jω
L ₂₂ ), the transfer function of the integrating circuit 23 is R ₂₃ /(R ₂₃ +j
ωL ₂₃ ). Here, R ₂₂ and R ₂₃ are the resistance values of the resistors 22-1 and 23-2, respectively, and L ₂₂ and L ₂₃ are the inductances of the coils 22-2 and 23-1, respectively. From this, 1≫ωL ₂₀ /R ₁₉ and 1≪
In the range that satisfies ωL ₂₁ /R ₂₂ , the differentiator circuit 2
2 is π/2, and the phase of the integrating circuit 23 is shifted by −π/2. And 1≫ω
It operates normally for all periodic tone signals that satisfy L ₂₂ /R ₂₂ , 1≪ωL ₂₃ /R ₂₃ , and
Resistors 22-1, 23-2 and coils 22-2, 23
It can be seen that this is not easily affected by variations in the value of -1.

As is clear from the above description, the present invention has the advantage that, with a simple circuit configuration, it is possible to correctly detect periodic tone signals in a wide frequency range without being affected by fading. , a great effect can be obtained to improve the reliability and economic efficiency of the receiving system.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a conventional signal detection circuit, FIG. 2 is a diagram showing the configuration of a first embodiment according to the present invention, and FIG. 3 is a diagram explaining the operation of the embodiment of FIG. 2. FIG. 4 is a diagram showing the configuration of a second embodiment according to the present invention. In the figure, 11 and 21 are demodulation circuits, 12 and 2
2 is a differentiating circuit, 13, 23 is an integrating circuit, 14, 2
4 is a comparison circuit, 12-1, 13-2 are capacitors, 12-2, 13-1, 22-1, 23-2 are resistors, and 22-2, 23-1 are coils.

Claims (1)

[Scope of Claims] 1. A differentiation circuit that receives a periodic tone signal obtained through a demodulation circuit and differentiates the tone signal; and an integration circuit that also receives the tone signal and integrates the tone signal; A tone signal detection circuit in a radio communication receiver, comprising a comparison circuit that compares an output of the differentiation circuit and an output of the integration circuit, and detects the periodic tone signal from the comparison circuit. 2. In the tone signal detection circuit according to claim 1, the differentiating circuit is configured by connecting a first capacitor and a first resistor, and the integrating circuit is configured by connecting a second resistor and a second resistor. A tone signal detection circuit in a wireless communication receiver, characterized in that it is configured by connecting a capacitor. 3. In the tone signal detection circuit according to claim 1, the differentiating circuit is configured by connecting a first resistor and a first coil, and the integrating circuit is configured by connecting a second coil and a second coil. A tone signal detection circuit in a wireless communication receiver, characterized in that the tone signal detection circuit is configured by connecting a resistor.