JPH02276356A - Frequency detecting circuit - Google Patents

Abstract

PURPOSE:To detect a frequency independently of the frequency of a reception signal by providing a means which analyzes the frequency of a reception signal in accordance with the time of one period of the reception signal to discriminate whether the pertinent frequency is detected or not as well as a means which uses a band pass filter to detect whether the frequency is detected or nor in accordance with the power of a desired frequency component. CONSTITUTION:When a control signal 102 is in the low level, a PCM signal is inputted to a frequency analyzing detection circuit 3 and is stored in a register and is inputted to a counter. Then, the desired frequency is detected in accordance with the time of one period. When the control signal 102 is in the high level, the PCM signal is inputted to a power analyzing detection circuit 4 to detect a synthesized frequency. A synthesizing circuit 5 outputs the result of frequency undetection when the frequency is not detected as results of both circuits, and the circuit 5 outputs the result of frequency detection when the frequency is detected as results of the circuit 3 and/or the circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency detection circuit, and more particularly to a frequency detection circuit using digital signal processing in a facsimile machine.

[Conventional technology]

The procedure for facsimile transmission in the general switched telephone network is
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There are a tonal procedure and a binary procedure.The former tonal procedure is aimed at analog facsimiles and is a simple procedure in which a single frequency is assigned to a control function for transmission and reception. The facsimile machine detects from the received signal which single frequency is assigned, and is controlled according to the function of that signal. Therefore, the detection time and reliability of the frequency detection circuit are important factors that determine the overall functionality of the facsimile machine.

Conventionally, when detecting frequency f by digital signal processing, the analog reception signal from the telephone line is converted into a digital signal by A/D conversion, and then input to a digital bandpass filter that passes only the frequency f component. Detection or non-detection of the frequency is identified by measuring the power of the output signal and referring to the output power level. What is shown in FIG. 3 is a block diagram showing the configuration of a conventional single frequency detection circuit, taking as an example the case of a PCM signal as a digital signal. 'D converter 12
and a power analysis and detection circuit 13 including a bandpass filter 14, a power detection circuit 15, and an identification circuit 16.

In FIG. 2, an analog reception signal inputted from a predetermined telephone line is inputted to an A/'D converter 12 and converted into a PCM signal of a nano-19f frequency F3. A,
, the PCM signal output from the /D converter 12 is passed through a bandpass filter 171 that passes only a specific frequency f.
, and only the component of frequency f is selected and output. The output signal of the bandpass filter 14 is input to a power detection circuit 15, and its power is measured and output. In the identification circuit 16, the power output of the power detection circuit 15 is input, and when the power output is larger than a predetermined appropriate value, it is identified as detected, and when it is smaller than k, it is identified as not detected, Detection or non-detection of the frequency f component is identified and the identification result is output.

[Problem to be solved by the invention]

In the conventional frequency detection circuit described above, the power of one frequency Qf component is measured using a bandpass filter that passes only the frequency f component, and based on the power, it is determined whether a single frequency is detected or not. There is.

As described above, since a bandpass filter is used to detect the frequency f component, a certain amount of response time is required to obtain a suitable output from a signal input.

This response time is determined by the time constant of the band-pass filter, and if the frequency you want to detect is low, it takes more time to input one cycle, so it takes more time to input one cycle than when the frequency is high. It takes time.

41"4 (a> and (b)) are diagrams showing the difference in response time due to the difference in the number of 1M waves to be detected, and the rise of the power output when the frequency to be detected is high and low, respectively. Obviously, when the frequency is high, the power output reaches a level exceeding the reference value k within a predetermined time, but when the frequency is low, the power output reaches a level exceeding the reference value k within a predetermined time. , and the reference value k
I can't reach it. In other words, for low frequencies,
Frequency cannot be detected within 1 m at a given time.

On the other hand, according to CCITT Recommendation 'r.30, it is necessary for facsimile machines to detect frequencies as low as 46211z. What is shown in FIG. 5 is an example of the reception timing in a conventional frequency detection circuit. Even if an attempt is made to detect the frequency t462Hz within a limited time of 5 to 6 ms from among the received signals 100, it will not be possible to detect the frequency t462Hz within a limited time of 5 to 6 ms. I couldn't get a good power rise, and 462t (
In other words, the conventional frequency detection circuit has the disadvantage that it cannot detect the frequency of z9, that is, it cannot comply with the CCITT Recommendation T.30.

[Means to solve the problem]

The frequency detection circuit of the present invention includes an A, -'D converter that inputs an analog reception signal input from a telephone line and converts it into a predetermined digital signal, and converts the digital signal via a predetermined control signal. A selection circuit that selects and outputs the first and second outputs by switching, and the output of Moe memory 1 are input, and frequency analysis is performed from the time of one cycle of the received signal, and a predetermined frequency is detected/undetected. a frequency analysis and detection circuit that identifies whether a predetermined frequency is detected or not detected through power analysis of frequency components by a digital filter using the output of the Moe memory 2 as input; A synthesis circuit inputs and synthesizes the output of the detection circuit and the output of the power analysis detection circuit.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram of a first embodiment of the invention. As shown in FIG. 1, this embodiment includes an A/'D converter 1, a selection circuit 20, a frequency analysis circuit 3, a power analysis detection circuit 4, and a synthesis circuit 5.

In FIG. 1, an analog received signal 1(]■ from a predetermined telephone line is converted into a PC~1 signal with a sampling frequency Fs by a D converter 1, and is outputted and input to a selection circuit 2. In the 9 selection circuit 2,
Controlled by a control signal 102 input from the outside,
When the control signal 102 is LOW, the PCM signal is output to the frequency analysis and detection circuit 3, and when the control signal 102 is old G11, the PCM signal is output to the power analysis and detection circuit 4.

The control signal 102 is LOIII, and the PCM signal is input to the frequency analysis detection circuit 3. Frequency analysis detection circuit 3
is composed of a register, a counter, and a frequency identification circuit (not shown) connected in series, and the P
The CM signal is input to a counter stored in a register. In counter and frequency identification circuits, PCM
Using the sign bit of the signal as an input, the change point of the received signal's sign bi.../1 is detected, and a desired frequency is detected from the time of the -period.

On the other hand, when the control signal 102 is the old GH and the PCM signal is input to the power analysis and detection circuit 4, the power analysis and detection circuit 4 uses the power analysis and detection circuit 13 in the conventional example described above (see FIG. ) Frequency detection is performed in the same manner as in the case of 1.

The frequency detection result of the frequency analysis detection circuit 3 described above (if the received digital signal is not input, it is output as undetected) and the frequency detection result of the power analysis detection circuit 4 (when the received digital signal is input) If the frequency detection results of both rows are not detected, output as undetected) is input to the combining circuit 5. In the combining circuit 5, if the frequency detection results of both rows are undetected, it is output as undetected. -H detection result is output as frequency detection.

Therefore, if the next received signal is at a high frequency such as 2100[(z or 1800Hz), the control signal 102 is set to the old GH, and the selection circuit 2
The power analysis detection circuit 3 converts the PCM signal into a selection action including 1
The frequency is detected by the power analysis detection circuit 3. In addition, if the next received signal has a low frequency such as 462Hz, the control signal 102 is set to LOIII, and the PC
The M signal is sent to the frequency analysis and detection circuit 3 to detect the frequency. Therefore, in this embodiment, even when the received signal has a low frequency, it can be adequately handled.

Next, a second embodiment of the present invention will be described. FIG. 2 is a block diagram of the second embodiment. As shown in FIG. 2, an A/D converter 6, a control circuit 7, a selection circuit 8, a frequency analysis detection circuit 9, a power analysis detection circuit 10 and a synthesis circuit ll.

The operation of the second embodiment shown in FIG. 2 is the same as that of the first embodiment described above, except for the operation of the control circuit 7. The control circuit 7 inputs the PCM signal output from the A/'D converter 6 and receives the ! (IGH or LO
A W control signal 103 is output and sent to the selection circuit 8. In this case, in the control circuit 7, if the frequency of the PCM signal input from the A, .D converter 6 exceeds a predetermined frequency, the control circuit 7 outputs the control signal 103 as the old GH,
If the frequency of the PCM signal is below the predetermined frequency, LO! Output as 'l. In the case of this second embodiment, since the control signal 103 is not input from the outside and the four wave numbers of the received signal are checked and output by itself, the selection circuit 8 selects the PCM signal. is automatically selected as IX without depending on an external control signal, and is sent to the frequency analysis and detection circuit 9 or the power analysis and detection circuit 11) to perform predetermined frequency detection.

(Effect of the invention〕

Claims (1)

[Claims] An A/D converter inputs an analog reception signal input from a telephone line and converts it into a predetermined digital signal, and selects the digital signal via a predetermined control signal and switches it as a first and second output. a frequency analysis and detection circuit that uses the first output as an input to perform frequency analysis from the time of one cycle of the received signal and identifies whether a predetermined frequency is detected or not; a power analysis detection circuit that uses the output as an input and identifies detection/undetection of a predetermined frequency through power analysis of frequency components by a digital filter; and an output of the frequency analysis detection circuit and an output of the power analysis detection circuit. A frequency detection circuit comprising: a synthesis circuit that receives input and synthesizes the input.