JP3204880B2 - Digital filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital filter for removing interference, which is mounted on a wireless communication device or the like.

[0002]

2. Description of the Related Art For example, when a receiver such as a wireless communication device receives an AM signal, an SSB signal, and a CW signal,
An interference wave may be mixed in the reception band, and a digital filter for interference removal shown in FIG. 4 is inserted in order to remove the mixed interference wave and increase the reception sensitivity.

In the case of the digital filter for interference cancellation shown in FIG. 4, a high frequency unnecessary component of an input signal 39 is filtered by a first analog low-pass filter 31, and then analog / digital conversion (hereinafter, referred to as A / D conversion). A digital signal is converted into a digital signal by a device 32, and an interfering wave or the like is filtered by a digital low-pass filter 33 and a digital high-pass filter 34, and only a desired digital signal is passed, and digital / analog conversion (hereinafter, referred to as D / A conversion). The demodulated signal 40 is returned to an analog signal by the filter 35, and a high-frequency unnecessary component generated at the time of D / A conversion is filtered by the second analog low-pass filter 36 to obtain a demodulated signal 40 from which interference has been removed.

In the above-described digital low-pass filter 33 and digital high-pass filter 34, some filter coefficients having different cutoff frequencies are stored in advance in coefficient bank memories 37 and 38, and the operator removes the interference removal digital signal shown in FIG. In order to obtain filter characteristics such that interference is removed while listening to the demodulated signal 40 from the filter, predetermined filter coefficients are extracted from the coefficient bank memories 37 and 38 by the selection signals 42 and 43, and the digital low-pass filter 33 and the digital The interference was removed by changing the cutoff frequency of the high-pass filter 34.

[0005]

In the conventional example shown in FIG. 4 described above, in order to smoothly change the digital low-pass filter 33 and the digital high-pass filter 34, the filter of the digital low-pass filter 33 and the digital high-pass filter 34 is required. The operable band is increased and the change width of the cutoff frequency is reduced. However, the capacity of the coefficient bank memory becomes enormous, and it is difficult to change the cutoff frequencies of the digital low-pass filter 33 and the digital high-pass filter 34 in a time shorter than the sampling time 41 for digitizing the input signal 39. Was.

When the filter coefficients of the digital low-pass filter 33 and the digital high-pass filter 34 are varied, unnecessary noise is generated, and the digital low-pass filter 33 and the digital high-pass filter 3
In order to obtain the same characteristics as in No. 4, there is a difference in the filter coefficient lengths, and if these were to be controlled by a computer, the process of changing the filter coefficients on a program became complicated.

In view of the above-mentioned problems of the prior art, the present invention shifts the frequency band of an input signal digitized by a digital multiplier so that unnecessary signals can be filtered by a preset digital filter, and It is an object of the present invention to obtain a digital filter capable of smoothly removing interference by filtering only a part without changing the characteristics of the digital filter.

[0008]

Means for Solving the Problems In order to achieve the above object, an analog / digital converter for digitizing an input analog signal, an output from the analog / digital converter as an input signal, and A first digital multiplier that multiplies the signal by a first discretized sine wave signal; a digital low-pass filter that takes an output from the first digital multiplier as an input signal and filters a high-frequency component of the input signal; A second digital multiplier for multiplying an output from the digital low-pass filter with a second discretized sine wave signal, and an output from the second digital multiplier as an input signal, and filtering a low-frequency component of the input signal A digital high-pass filter, a third digital multiplier that multiplies an output from the digital high-pass filter by a third discretized sine wave signal, and a third digital multiplier. And a digital-to-analog converter for converting the output signal of the digital signal into an analog signal, and obtaining an output analog signal obtained by filtering a desired unnecessary signal.

[0009]

In the digital filter according to the present invention, a high-frequency unnecessary signal of the input signal is high-pass filtered by a first analog low-pass filter, the signal is converted into a digital signal by an analog / digital converter, and the digital signal is converted by a first digital low-pass filter. High-pass filtering.

[0010] A first digital multiplier multiplies the digitized demodulated signal, which is within a pass band of a second digital low-pass filter set in advance, with a first discretized sine wave signal, and digitizes the signal. The first discretized sine wave signal is varied so that unnecessary signal components in the high frequency range of the demodulated signal are shifted out of the pass band of the second digital low-pass filter. A certain unnecessary signal component is filtered.

A second digital multiplication of the digitized demodulated signal within a preset digital high-pass filter passband to filter out unwanted signal components in the low band of the digitized demodulated signal. Multiplying the second discretized sine wave signal by a filter, and shifting the second discretized sine wave signal so as to shift unnecessary signal components in the low band of the digitized demodulated signal to outside the pass band of the digital high-pass filter. The variable and unnecessary signal components in the low band of the digitized demodulated signal are filtered.

After the unnecessary signals in the high band and the low band of the digitized demodulated signal are filtered out, a third digital multiplier converts the third discretized sine wave signal into the original frequency band in order to return to the original frequency band. To multiply.

As a result of multiplication by the third discrete sine wave signal,
Since unnecessary signals are generated in the high frequency band, high frequency filtering is performed by the third digital low pass filter.

The digital / analog converter converts the analog signal back into an analog signal. At this time, the unnecessary signal generated in the high frequency band is filtered by the second analog low-pass filter. Therefore, an output analog signal from which a desired unnecessary signal of the input analog signal has been removed can be obtained.

[0015]

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1, 2 and 3. FIG. FIG. 1 is a circuit diagram showing an embodiment of a digital filter according to the present invention, wherein 1 is a first analog low-pass filter, 2 is an analog / digital converter (hereinafter, referred to as an A / D converter), 3 Is a first digital low-pass filter, 4 is a first digital multiplier, 5 is a second digital low-pass filter, 6 is a second digital multiplier, 7 is a digital high-pass filter, 8 is a third digital multiplier, 9 is a third digital low-pass filter, 1
0 is a digital / analog converter (hereinafter referred to as a D / A converter), 11 is a second analog low-pass filter, 1
2 is a first discretized sine wave oscillator, 13 is a second discretized sine wave oscillator, and 14 is a third discretized sine wave oscillator.
Reference numeral 15 denotes an input signal (hereinafter, referred to as fin), 16 denotes an output signal (hereinafter, referred to as fout), 17 denotes a sampling frequency (hereinafter, referred to as fs), and 18 denotes a first discretized sine wave frequency (hereinafter, fosc1). , 19 is a second discretized sine wave frequency (hereinafter, fosc2), 20 is a third discretized sine wave frequency (hereinafter, fosc3), S1 is a first unnecessary signal, and S2 is A second unnecessary signal, S3 is a first unnecessary signal, S4 is a second unnecessary signal, S5 is a first unnecessary signal, and S6 is a third unnecessary signal.

While the operator listens to the demodulated signal of the wireless communication device equipped with the digital filter of the present invention shown in FIG. 1, the following operations are performed to remove unnecessary signals mixed in the band. Improve the receiving sensitivity, etc.

In FIG. 1, the fin 15 filters out the high frequency unnecessary components of the fin 15 by the first analog low-pass filter 1, and the A / D converter 2 digitizes the fin 15 at the sampling frequency fs and outputs it.

FIG. 2A shows a spectrum diagram when the fin 15 is A / D converted into a digital signal. In the present embodiment, the first unnecessary signal S is added to the digitized input signal.
It is assumed that there is a first and a second unnecessary signal S2, and the purpose is to eliminate these.

The digitized fin 15 is filtered by a first digital low-pass filter 3, as shown in FIG. 2 (b), for high-frequency components unnecessary for the processing of this embodiment, and input to a first digital multiplier. .

As shown in FIGS. 2 (c), 2 (d) and 2 (e), in order to remove the second unnecessary signal S2 located on the high frequency side of fin 15, the first digital multiplier fin 1
5 generates the fosc 118 from the first discretized sine wave oscillator 12 so that the portion of the second unnecessary signal S2 in FIG. 5 is located in the stop band of the second digital low-pass filter in FIG.
Is shifted to S4. At the same time, the first unnecessary signal S1 of fin 15 is converted to S3.

Next, in order to remove the first unnecessary signal S1 located on the low frequency side of the fin 15, FIG. 2 (f) and FIG.
As shown in (g) and (h) of FIG. 1, in the second digital multiplier, the portion of the first unnecessary signal S3 in the fin 15 frequency-converted by the first digital multiplier is replaced with the first unnecessary signal S3 in FIG.
Fosc 219 is generated from the second discretized sine wave oscillator 13 so as to be located in the rejection band of the digital high-pass filter, and fin 15 is shifted so that S3 becomes S5.

The fin 15 from which the two unnecessary signals have been removed generates a fosc 320 from the third discrete sine wave oscillator 14 in the third digital multiplier in order to return to the original frequency band. At this time, as shown in FIG.
15 is converted to the original frequency band.
Since the third unnecessary signal S6 is generated in the high frequency portion of FIG.
As shown in (j) and (k), the third unnecessary signal S6 is filtered by the third digital low-pass filter of FIG.

The fin 15 from which all unnecessary signals have been removed is
The signal is converted into an analog signal by the D / A converter 10 shown in FIG.
The high frequency unnecessary component generated at this time is filtered by the second analog low-pass filter 11 to obtain an output signal 16 from which a desired unnecessary signal has been removed.

[0024]

As described above, the digital filter of the present invention can use a digital filter having constant cutoff characteristics and frequency characteristics, so that the required memory capacity can be extremely reduced. In addition, since a desired unnecessary signal is removed by changing the discretized sine wave signal without switching the filter characteristics, interference can be removed smoothly, and the reception sensitivity and the like can be improved.

In view of the recent development of microcomputer technology and the like, various data processing and signal processing are performed at a high speed, so that the responsiveness of the frequency conversion and filtering by a digital filter of the present invention becomes extremely fast. Considered and practical, the digital filter of the present invention has an extremely excellent effect in removing interference of a wireless communication device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a transition diagram of each signal in one embodiment of the present invention.

FIG. 3 is a transition diagram of each signal in one embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st analog low pass filter 2 analog / digital converter 3 1st digital low pass filter 4 1st digital multiplier 5 2nd digital low pass filter 6 2nd digital multiplier 7 digital high pass filter 8 3rd digital Multiplier 9 Third digital low-pass filter 10 Digital / analog converter 11 Second analog low-pass filter 12 First discretized sine wave oscillator 13 Second discretized sine wave oscillator 14 Third discretized sine wave oscillator 15 Input signal 16 Output signal 17 Sampling frequency 18 First discrete sine wave signal 19 Second discrete sine wave signal 20 Third discrete sine wave signal 31 First analog low-pass filter 32 Analog / digital converter 33 Digital Low-pass filter 34 Digital high-pass filter Reference Signs List 5 digital / analog converter 36 second analog low-pass filter 37 coefficient bank memory 38 coefficient bank memory 39 input signal 40 output signal 41 sampling time 42 selection signal 43 selection signal S1 first unnecessary signal S2 second unnecessary signal S3 1 unnecessary signal S4 2nd unnecessary signal S5 1st unnecessary signal S6 3rd unnecessary signal

Claims (1)

(57) [Claims] An analog-to-digital converter for digitizing an input analog signal, and a first converter that takes an output from the analog-to-digital converter as an input signal and multiplies the input signal by a first discrete sine wave signal. And a digital multiplier of
A digital low-pass filter that takes an output from the digital multiplier as an input signal and filters a high-frequency component of the input signal, and a second digital that multiplies the output from the digital low-pass filter by a second discretized sine wave signal A multiplier and the second
A digital high-pass filter that takes an output from the digital multiplier as an input signal and filters a low-pass component of the input signal, and a third digital that multiplies an output from the digital high-pass filter by a third discretized sine wave signal A multiplier and the third
A digital / analog converter for converting an output signal from the digital multiplier into an analog signal, and obtaining an output analog signal obtained by filtering a desired unnecessary signal.