JP2002057553A - Digital filtering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a digital filtering device capable of reducing the number of parts. SOLUTION: This device is installed with plural filter modules 4 provided with an adder 2, a feedback loop 6 connected to this adder 2 and an FIR filter 3 located on this feedback loop 6. By changing over an output selecting switch 5, the FIR filter 3 to extract an output signal can be selected. Besides, by supplying the coefficient data of the FIR filter to the FIR filters 3, which are not selected by the output selecting switch 5, processing for rewriting the coefficients of the filters is performed. Thus, rewriting processing of coefficients is enabled and continuous filter outputs can be provided. Further, since the adder 2, the FIR filter 3 and the feedback module 6 are made into module, the number of parts comprising a relevant digital filtering device 1 can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital filter device having a bank switching function capable of selectively extracting and outputting output signals of a plurality of digital filters.

[0002]

2. Description of the Related Art For example, an echo canceller or a ghost canceller used in a communication system is equipped with a digital filter device having a feedback loop for an input digital signal.

FIG. 3 is a block diagram showing the configuration of a digital filter device used for such a purpose. As shown in FIG.
Reference numeral 1 denotes an adder 22, a feedback loop 24 for feeding back an output signal of the adder 22, an FIR filter 23 disposed on the feedback loop 24, a stage preceding the adder 22, and an FIR filter 2
3 and delay latches 26 and 27 disposed at the preceding stage of the FIR filter 3. The output of the FIR filter 23 is supplied to the adder 22.

As is well known, various coefficients are set in the FIR filter 23, and the frequency is appropriately changed based on the coefficient data supplied from the signal line 25 of the FIR filter coefficient. The characteristics of the FIR filter 23 such as the cutoff characteristics can be changed to desired characteristics. Here, in the FIR filter 23 used as an echo canceller or a ghost canceller,
It is necessary to change the characteristics of the FIR in various ways. In this case, it is necessary to rewrite the coefficient set in the FIR filter 23 in real time.

However, the FIR filter 23 cannot obtain an accurate output immediately after rewriting the coefficients.
After new data is input to all taps of the R filter 23 (that is, after the coefficients have been rewritten, clock signals have been input for the number of taps of the FIR filter 23), a normal output is obtained. Therefore, the FIR filter 23
When it is necessary to rewrite the coefficients, the digital filter device 21 cannot be operated continuously.

In order to solve such a problem, a digital filter device having a bank switching function has been conventionally proposed and put to practical use.

FIG. 4 is a block diagram showing the configuration of a conventional digital filter device 31 having a bank switching function. As shown in FIG. 4, the digital filter device 31 includes an adder 32 and the adder 32. And two feedback loops 34a and 34b for feeding back the output signal of Further, FIR filters 33a and 33b are disposed on the feedback loops 34a and 34b, respectively.
a, 33b are output from the switching output selection switch 3
5 is fed back to the adder 32.

Further, latches 38a and 38b are provided at a stage preceding the FIR filters 33a and 33b.
Are provided on the input side.

A signal line 36 for transmitting FIR coefficient data supplied from the outside is connected to a coefficient selection switch 3.
7, and is connected to FIR filters 33a and 33b. If two switches (output selection switch 35 and coefficient selection switch 37) are switched in synchronization with each other in synchronization with a switching signal given from the outside, when the output of one FIR filter is selected, the other is selected. The operation of rewriting the coefficient of the FIR filter can be performed.

With this configuration, it is possible to write the coefficients into the FIR filter and to continuously obtain the output signal from the FIR filter.

[0011]

However, in the above-described conventional digital filter device 31, although a continuous filter output can be obtained by performing bank switching, an adder 32 and two FIR filters 3 are used.
3a, 33b, and two switches (output selection switch 35, coefficient selection switch 37) are required, and there is a disadvantage that the number of components is large.

Further, each of the feedback loops 34a, 34a
Since the latches 38a and 38b are provided on the 4b and the latch 40 is provided before the adder 32, there are a total of two latches on the feedback loop, and the delay time becomes longer. There was a problem.

The present invention has been made to solve such a conventional problem, and it is an object of the present invention to reduce the number of parts and to reduce delay time on a feedback loop. It is an object of the present invention to provide a digital filter device that can be implemented.

[0014]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 of the present application provides an arithmetic unit, a feedback loop connected to an output terminal of the arithmetic unit, and a feedback loop disposed on the feedback loop. And a digital filter having an output terminal connected to the operation unit. The output terminal of the operation unit mounted on one selected filter module among the filter modules. And a feedback loop of the filter module, and a coefficient data signal for rewriting a coefficient set in the digital filter should be supplied to another filter module different from the selected one filter module. Switching means for performing a switching operation, wherein the output signal of the selected one filter module is It is characterized in that the output signal of the digital filter device.

According to a second aspect of the present invention, there is provided an arithmetic unit, a feedback loop connected to the output terminal of the arithmetic unit, and a digital filter arranged on the feedback loop and having an output terminal connected to the arithmetic unit. And connecting the output end of a computing unit mounted on one of the filter modules selected from the filter modules, and a feedback loop of the filter module, and Switching means for switching a coefficient data signal for rewriting a coefficient set in the digital filter to be supplied to the other filter module different from the one filter module, and comprising an output signal of the one filter module. Is an output signal of the digital filter device.

According to a third aspect of the present invention, the digital filter is any one of an FIR filter, an IIR filter and a lattice filter. The invention according to claim 4 is characterized in that the arithmetic unit is one of an adder and a multiplier.

In the present invention configured as described above, a plurality of filter modules formed by an arithmetic unit, a digital filter, and a feedback loop are provided, and among them, one selected filter module is used.
The input signal is filtered and output. In a filter module different from the selected one filter module, a process of rewriting the coefficients of the digital filter is performed. Therefore, the coefficients of the digital filter can be appropriately rewritten, and a continuous filter output can be obtained.

Further, since the arithmetic unit, the digital filter, and the feedback loop are modularized, the number of components can be reduced, and the work such as mounting work can be reduced. Further, the delay time on the feedback loop can be reduced.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of a digital filter device to which the present invention is applied. As shown in FIG. 1, the digital filter device 1 includes two filter modules 4a and 4b. Each of the filter modules 4a and 4b includes adders 2a and 2b and FIR filters 3a and 3b, respectively.
And the latches 9a, 9b arranged before the adders 2a, 2b.
9b, and latches 10a and 10b disposed in front of the FIR filters 3a and 3b. Further, the digital filter device 1 includes an output selection switch 5,
It has a coefficient selection switch 7.

The latches 9a, 9b, 10a and 10b
It is constituted by a flip-flop and delays an input signal by one clock. When high-speed processing is not required, the latches 9a, 9b, 10a, and 10b need not be provided.

Each of the adders 2a, 2b has a latch 9a, 9
Input data is supplied via each of b. The outputs of the adders 2a and 2b are connected to the contacts 5a and 5b of the output selection switch 5, and the common contact 5c of the output selection switch 5 is branched into three systems. Of these, 1
The first branch line is connected to the FIR filter 3a via the feedback loop 6a and the latch 10a, and the second branch line is connected to the FIR filter 3b via the feedback loop 6b and the latch 10b. ,
The third branch line is an output line of the digital filter device 1.

The FIR filters 3a and 3b are connected to the contacts 7a and 7b of the coefficient selection switch 7, respectively.
A signal line 8 for transmitting coefficient data of the filter is connected. The coefficient selection switch 7 and the output selection switch 5 are switched in conjunction with each other. When the output signal of one of the filter modules 4a is selected by the output selection switch 5,
The coefficient selection switch 7 operates to connect the signal line 8 to the FIR filter 3b side of the other filter module 4b.

Next, the operation of the digital filter device 1 configured as described above will be described. When a switching signal is given to the output selection switch 5 and the coefficient selection switch 7 that operate in conjunction with each other, and the contacts 5a and 5c and the contacts 7b and 7c are connected, the filter module 4a Since the operation is performed, the input data supplied to the adder 2a is supplied to the FIR filter 3a via the output selection switch 5, the feedback loop 6a, and the latch 10a, and the output of the FIR filter 3a is fed back to the adder 2a. Is done. Then, a signal obtained at the common contact 5 c of the output selection switch 5 is used as an output signal of the digital filter device 1.

Since the FIR coefficient data is supplied to the FIR filter 3b via the signal line 8 and the coefficient selection switch 7, the FIR filter 3b performs a rewriting process of the filter coefficient. During this time, the FIR filter 3
b does not output a signal.

Next, when the connection of the output selection switch 5 and the connection of the coefficient selection switch 7 are switched by the switching signal, the contacts 5b and 5c and the contacts 7a and 7c are connected, and the input data is The data is filtered and output by the FIR filter 3b on the filter module 4b side. During this time, the coefficient of the FIR filter 3a is rewritten.

By performing such a bank switching operation, when one FIR filter is used, the coefficient of the other FIR filter can be rewritten, so that a continuous filter output can always be obtained. it can.

An adder 2 (2a, 2b) and an FIR
A filter module 4 (4a, 4b) is formed by the filters 3 (3a, 3b), and a digital filter is formed by an output selection switch 5 and a coefficient selection switch 7 that operate in conjunction with the two filter modules 4a, 4b. Since the filter device 1 is configured, the number of parts can be reduced as compared with the related art.

That is, in the conventional digital filter device 31 shown in FIG. 4, two FIR filters 33a,
Since the module 33b and the adder 32 are formed as separate modules, a total of three modules are required. However, in the digital filter device 1 according to the present embodiment, only two filter modules 4a and 4b are required. Therefore, the number of parts can be reduced. Thereby, the efficiency of the operation when mounting the module can be improved.

Further, by reducing the number of modules, the amount of delay on the feedback loops 6a and 6b (the signal output from the adders 2a and 2b is fed back to the input to the adders 2a and 2b again). Delay time) can be shortened. That is, a commonly used module has a latch (D-type flip-flop) mounted at a signal input terminal in many cases in order to compensate timing between the module and another module. Therefore, as the number of modules increases, the amount of delay on the feedback loop increases accordingly, and conversely, as the number of modules decreases, the amount of delay on the feedback loop decreases accordingly. In the present embodiment, the delay time can be reduced by reducing the number of modules.

Specifically, in the filter device 1 shown in FIG.
One latch 1 is provided on the feedback loops 6a and 6b.
0a and 10b are arranged, whereas FIG.
In the conventional filter device 31 shown in FIG. 2, two latches 38a (or 38b), 40
Since the two latches are arranged, the delay time can be reduced in the filter device 1 shown in FIG. The above effects (effects of reducing the delay time in the feedback loop) are applied to the configuration in which the latch is not used in the module.
Is not achieved.

The conventional filter device 3 shown in FIG.
In the case of 1, since the adder 32 is arranged at the subsequent stage of the output selection switch 35, after the output selection switch 35 is switched,
In contrast to the delay caused by the processing of the adder 32, in the present embodiment, as shown in FIG. 1, the output selection switch 5 is provided at the subsequent stage of the adders 2a and 2b. After the switching, no delay occurs due to the processing of the adders 2a and 2b.

Further, in the digital filter device 1 according to the present embodiment, since the adder 2 (2a, 2b) and the FIR filter 3 (3a, 3b) are modularized, as shown in FIG. The filter modules 4a and 4b are separated from each other, and separate digital filter devices 11a and
11b can also be used. This is FI
This is effective when the digital filter is used as a digital filter that does not require rewriting of coefficients to the R filter 3 (3a, 3b).

In the above embodiment, the adder 2
(2a, 2b) and two filter modules 4 (4a, 4b) each having an FIR filter 3 (3a, 3b), and an example in which these outputs are switched and used, has been described. It is not limited to this,
It is also possible to provide a configuration in which three or more filter modules 4 are installed and the output signals of the three or more filter modules 4 are selectively taken out by bank switching.

In this embodiment, an example in which the FIR filter 3 (3a, 3b) is used as a digital filter has been described. However, the present invention is not limited to this, and an IIR filter, a lattice filter, or the like may be used. Can be used. Furthermore, in the present embodiment, an example has been described in which the adder 2 (2a, 2b) is used as a computing unit disposed before the FIR filter 3 (3a, 3b), but the present invention is not limited to this. Instead, another arithmetic unit such as a multiplier can be used.

[0035]

As described above, according to the digital filter device of the present invention, a plurality of filter modules each including a computing unit, a digital filter, and a feedback loop for feeding back the output of the digital filter to the computing unit are arranged. Since these components are connected to form a digital filter device, the number of components can be reduced as compared with a conventional digital filter device. As a result, it is possible to reduce the labor required when mounting components.

Also, since the number of modules can be reduced, the delay time in the feedback loop can be reduced. Further, separating the filter modules makes it possible to use them as separate filter modules.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital filter device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example in which two filter modules constituting a digital filter device according to an embodiment of the present invention are separated and configured.

FIG. 3 is a block diagram showing a configuration of a conventional digital filter device.

FIG. 4 is a block diagram showing a configuration of a conventional digital filter device having a bank switching function.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Digital filter device 2 (2a, 2b) Adder (calculator) 3 (3a, 3b) FIR filter (digital filter) 4 (4a, 4b) Filter module 5 Output selection switch 6 (6a, 6b) Feedback loop 7 Coefficient Selection switch 8 Signal line 9 (9a, 9b) Latch 10 (10a, 10b) Latch 11a, 11b Digital filter device

Claims (4)

[Claims] 1. A filter module comprising: a computing unit; a feedback loop connected to an output terminal of the computing unit; and a digital filter disposed on the feedback loop and having an output terminal connected to the computing unit. Connecting a plurality of output terminals of a computing unit mounted on one selected filter module among the filter modules and a feedback loop of the filter module;
And a switching means for performing a switching operation to supply a coefficient data signal for rewriting a coefficient set in the digital filter to another filter module different from the selected one filter module. A digital filter device, wherein an output signal of one filter module is used as an output signal of the digital filter device. 2. A filter module comprising: a computing unit; a feedback loop connected to the computing unit output terminal; and a digital filter disposed on the feedback loop and having an output terminal connected to the computing unit. And connecting an output terminal of a computing unit mounted on one of the filter modules selected from the filter modules and a feedback loop of the filter module;
And switching means for performing a switching operation for supplying a coefficient data signal for rewriting a coefficient set in the digital filter to the other filter module different from the one filter module, comprising: an output of the one filter module. A digital filter device, wherein a signal is an output signal of the digital filter device. 3. The digital filter device according to claim 1, wherein the digital filter is one of an FIR filter, an IIR filter, and a lattice filter. 4. The digital filter device according to claim 1, wherein the arithmetic unit is one of an adder and a multiplier.