JPH0150151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-frequency signal receiver, and more particularly to a multi-frequency signal receiver using discrete Fourier transform.

As telephone exchanges and other communication paths become time-divided, push-button dial signal receivers (PB receivers)
Or receive multi-frequency signals used between stations
Multi-frequency signal receivers such as MF receivers are also being digitized to maintain compatibility with communication channels. When digitizing these multi-frequency signal receivers, attempts have been made to use discrete Fourier transform in order to detect a signal of a predetermined frequency contained in an input signal.

FIG. 1 is a diagram showing an example of the configuration of a conventional multi-frequency signal receiver. In FIG. 1, when the input signal f(nT) (T is the sampling period) is input from the terminal 1, it is multiplied by the rectangular window function supplied from the window function generator 7 by the multiplier 30, and the time T ₀ Only the calculation interval of is extracted. The output of the multiplier 30 is supplied with a kernel having the required detection angular frequency ω supplied from the window function generator 7 by multipliers 31 and 32.
cosnωT and sinnωT are respectively multiplied.
The outputs of multipliers 31 and 32 are input to an accumulator consisting of adders 41 and 42 and one sampling period delay registers 51 and 52, and are accumulated over the operation interval (time T ₀ ). The accumulator output Fc
and Fs are shown by equation (1).

However, N is the number of input signal samples input within the calculation interval (time T ₀ ). The accumulator outputs
After sending out Fc and Fs, it is reset by gates 61 and 62. The accumulator outputs Fc and Fs are squared by multipliers 33 and 34, respectively, and then added by an adder 43, and an adder output F proportional to the amplitude of the desired detected angular frequency ω component is sent to the terminal 2.

|F| ² =Fc ² +Fs ² (2) Based on the magnitude of the adder output F, it is determined whether there is an input signal having the required detection angular frequency ω.

As is clear from the above explanation, in a conventional multifrequency signal receiver, the kernels cosnωT and SinnωT having the required detection angular frequency ω are used for each multifrequency signal (for example, for the PB signal, eight frequencies from 697 Hz to 1633 Hz, for the MF signal 700 hertz to
6 frequencies of 1700 Hz). Conventionally, in order to obtain these kernels, the greatest common divisor of signal frequencies constituting a multi-frequency signal is sampled with a period T and stored in a storage device, and addresses of the storage device are specified at appropriate intervals to retrieve the stored samples. This required methods such as reading the value. For example, to obtain the PB signal digit by 8 kHz sampling, it is necessary to store samples of the greatest common divisor, 1 Hz, in an 8 kHz storage device, and read them from the storage device at intervals of addresses 697 to 1633. It requires a large storage capacity and multiple control circuits.

The purpose of the present invention is to eliminate the drawbacks of conventional multi-frequency signal receivers as described above, and to realize a multi-frequency signal receiver that can perform discrete Fourier transform without using large-scale and complicated nuclear generation means. be.

The purpose of this is to provide a first means of multiplying the input signal by a window function in a multi-frequency signal receiver using discrete Fourier transform, and a filter coefficient of e ^j 〓 ^T (ω is the required detection angular frequency, T is the sampling period ), which has a function of being reset at a period determined by the window function, and which inputs the output of the first means; and a real part output and an imaginary part output of the primary cyclic digital filter. and second means for obtaining an output proportional to the amplitude of the desired detection angular frequency of the input signal, and determining the presence or absence of an input signal having the desired detection angular frequency based on the output value of the second means. achieved.

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. FIG. 2 is a principle diagram of a primary recursive digital filter according to an embodiment of the present invention.
FIG. 3 is a diagram showing the configuration of a multi-frequency signal receiver according to an embodiment of the present invention. In FIG. 2, the input signal f(nT) input from the terminal 1 is multiplied by a rectangular window function by the multiplier 30, and only the calculation interval of time T ₀ is extracted and input to the adder 4. The adder 4, the one-sampling period delay register 5, and the multiplier 3 that multiplies the filter coefficient e ^j 〓 ^T constitute a primary cyclic digital filter. Note that the initial value of the one sampling period delay register 5 is reset to 0 by the gate 6. Now sample point 0 from multiplier 30
When an input signal f(0) is output at , the filter output Fe produced at the terminal 21 is equal to the input signal f(0). Input signal f(T) from multiplier 30 to next sampling point T
is input, the filter output produced at terminal 21
Fe is represented by formula (3).

Fe=f(0)e ^j 〓 ^T +f(T) (3) Similarly, when the input signal f(nT) is sequentially input from the multiplier 30 to the sample points nT (n is 0 to N-1), The filter output Fe generated at the terminal 21 at the sampling point (N-1)T is expressed by equation (4).

Fe= _N-1 〓 ⁿ⁼⁰ f(nT)e ^j(Nn-1) 〓 ^T (4) Equation (4) is the kernel cosnωT and sinnωT in equation (1)
It is nothing but a complex representation of , with the order reversed. Since reversing the order of the kernels does not affect the calculation result, equation (4) can be regarded as the calculation result of the desired discrete Fourier transform. Based on the above principle, the multi-frequency signal receiver shown in FIG. 3 is constructed. In FIG. 3, adders 43, 44 and 45, multiplier 35,
36, 37 and 38 and one sampling period delay registers 50 and 51 constitute a primary cyclic digital filter similar to that shown in FIG.
Output each. In FIG. 3, when the input signal f(nT) is input from terminal 1, it is multiplied by the rectangular window function supplied from the window function generator 70 by the multiplier 30, and only the calculation interval of time T ₀ is extracted. . The output f(nT) of the multiplier 30 (n is 0 to N
-1) is input to the adder 43, the first-order recursive digital filter executes a discrete Fourier transform based on the principle shown in FIG. The indicated real part output F′c
and the imaginary part output F's is at terminals 21r and 21i
is output to.

These real part output F'c and imaginary part output F's are squared by multipliers 33 and 34, respectively, as in FIG. The adder output F' is sent to terminal 2.

|F′| ² =F′c ² +F′s ² (6) The presence or absence of an input signal having the required detection angular frequency ω is determined based on the magnitude of the adder output F′.

As is clear from the above description, according to this embodiment, the kernels cosnωT and sinnωT are generated equivalently by a first-order cyclic digital filter, and no special kernel generation circuit is required.

Note that FIG. 3 is only one embodiment of the present invention, and the window function supplied from the window function generator 70 is not limited to a rectangular shape, and the present invention can also be applied to other types of window functions. The effect of the invention remains the same.

As described above, according to the present invention, in a multi-frequency signal receiver using discrete Fourier transform, kernel generation is equivalently performed by a first-order recursive digital filter, eliminating the need for large-scale and complicated kernel generation means.
The multi-frequency signal receiver is made economical and compact.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a conventional multi-frequency signal receiver, FIG. 2 is a principle diagram of a primary recursive digital filter according to an embodiment of the present invention, and FIG. 3 is a diagram according to an embodiment of the present invention. FIG. 3 is a diagram showing the configuration of a multifrequency signal receiver. 1, 2, 21, 21r and 21i in the figure
is a terminal, 7 and 70 are window function generators, 5, 50
and 51 are one sampling period delay registers, 3, 3
0, 31, 32, 33, 34, 35, 36, 37
and 38 is a multiplier, 4, 40, 41, 42, 4
3, 44 and 45 indicate adders.

Claims (1)

[Claims] 1 In a multi-frequency signal receiver using discrete Fourier transform, the first means of multiplying the input signal by a window function and the filter coefficient e ^j 〓 ^T (ω is the required detection angular frequency,
a first-order recursive digital filter having a function of being reset at a period determined by the window function and inputting the output of the first means; and a real number part of the first-order recursive digital filter. and a second means for obtaining an output proportional to the amplitude of the desired detection angular frequency of the input signal from the output and the imaginary part output, and the presence or absence of an input signal having the desired detection angular frequency is determined by the output value of the second means. A multi-frequency signal receiver characterized by determining.