JPH0946249A - Digital filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a desired spurious signal and to smoothly eliminate radio interference by providing an A/D converter, plural digital multipliers, discretizing sine wave oscillators, digital LPF, digital HPF and a D/A converter. SOLUTION: Analog LPF 1 filters a high-band undesired component in an input signal 15, and the A/D converter 2 digitalizes the signal by a sampling frequency. Then, it is outputted to digital LPF 3. The digital multipliers 4, 6 and 8 receive signals 18, 19 and 20 from the discretizing sine wave oscillators 12, 13 and 14 and convert the frequencies. The output of the multiplier 4 is inputted to digital LPF 5, the output of the multiplier 6 to digital HPF 7 and the output of the multiplier 8 to digital LPF 9. They filter the unnecessary signals. The signals from which the spuriousary signals are eliminated are converted into analog signals by the D/A converter 10, the high-band undesired component generated at this time is eliminated by analog LPF and an output signal 16 from which the desired spurious signal is eliminated is obtained.

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,
Interference waves may be mixed in the reception band, and the interference removal digital filter shown in FIG. 4 is inserted to remove the mixed interference waves and increase the reception sensitivity.

In the case of the interference removing digital filter shown in FIG. 4, the high frequency unnecessary component of the input signal 39 is filtered by the first analog low-pass filter 31, and then analog / digital conversion (hereinafter referred to as A / D conversion). ) Device 32 converts the signal into a digital signal, and digital low-pass filter 33 and digital high-pass filter 34 filter the interfering wave and the like to pass only a desired digital signal, and digital / analog conversion (hereinafter referred to as D / A conversion). The analog signal is returned to the analog signal by the device 35, and unnecessary components in the high frequency band generated at the time of D / A conversion are filtered by the second analog low-pass filter 36 to obtain the demodulated signal 40 with interference removed.

In the above-described digital low-pass filter 33 and digital high-pass filter 34, some filter coefficients having different cut-off frequencies are stored in advance in the coefficient bank memories 37 and 38, and the operator can perform the digital signal for removing interference shown in FIG. While listening to the demodulated signal 40 from the filter, in order to obtain a filter characteristic such that interference is removed, 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 low-pass filter 33 are used. Interference was removed by changing the cutoff frequency of the high-pass filter 34.

[0005]

In order to smoothly vary the digital low-pass filter 33 and the digital high-pass filter 34 in the conventional example shown in FIG. 4, the filters of the digital low-pass filter 33 and the digital high-pass filter 34 are changed. Increase the operable band and reduce the change width of the cutoff frequency. However, the capacity of the coefficient bank memory becomes huge, 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. It was

In the digital low-pass filter 33 and the digital high-pass filter 34, when each filter coefficient is changed, unnecessary noise is generated, and the digital low-pass filter 33 and the digital high-pass filter 3 are generated.
When trying to obtain the same characteristics in 4 and 4, there arises a difference in the filter coefficient lengths, and if these are controlled by a computer, the process of changing the filter coefficient on the program becomes complicated.

In view of the problems of the conventional example described above, in the present invention, the frequency band of the input signal digitized by the digital multiplier is shifted so that the unwanted signal can be filtered by the preset digital filter. An object of the present invention is to obtain a digital filter that can smoothly remove interference without changing the characteristics of the digital filter by filtering only the portion.

[0008]

In order to achieve such an object, an analog / digital converter for digitizing an input analog signal, and an output from the analog / digital converter as an input signal A first digital multiplier for multiplying the first discretized sine wave signal; a digital low-pass filter for filtering the high-frequency component of the input signal using the output from the first digital multiplier as an input signal; A second digital multiplier that multiplies the output from the digital low-pass filter and the second discretized sine wave signal, and filters the low-pass component of the input signal using the output from the second digital multiplier as an input signal. A digital high-pass filter, a third digital multiplier that multiplies the output from the digital high-pass filter by a third discretized sine wave signal, and the third digital multiplier And a digital / analog converter for converting the output signal of FIG. 4 into an analog signal, and obtaining an output analog signal obtained by filtering a desired unnecessary signal.

[0009]

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

The digitized demodulated signal, which is within the pass band of the preset second digital low-pass filter, is multiplied with the first discretized sine wave signal by the first digital multiplier and digitized. The first discretized sine wave signal is varied so that unnecessary signal components in the high frequency band of the demodulated signal are shifted to the outside of the pass band of the second digital low-pass filter, and the high frequency band of the digitized demodulated signal is obtained. Filter out some unwanted signal components.

A second digital multiplication is performed on the digitized demodulated signal within a pass band of a preset digital high-pass filter in order to filter unnecessary signal components in the low band of the digitized demodulated signal. The second discretized sine wave signal is multiplied by the second discretized sine wave signal in the converter to shift the unnecessary signal component in the low frequency band of the digitized demodulated signal to the outside of the pass band of the digital high pass filter. Variable to filter out unwanted signal components in the low band of the digitized demodulated signal.

After filtering the unwanted signals in the high and low frequencies of the digitized demodulated signal, the third digital multiplier multiplies the third discretized sine wave signal in order to restore the original frequency band. Use to multiply.

As a result of multiplication by the third discretized sinusoidal signal,
Since an unnecessary signal is generated in the high frequency band, high frequency filtering is performed by the third digital low pass filter.

Again, in order to return to an analog signal, it is converted into an analog signal by a digital / analog converter. The unnecessary signal generated in the high frequency band at this time is filtered by the second analog low-pass filter. Therefore, it is possible to obtain an output analog signal from which a desired unnecessary signal of the input analog signal is removed.

[0015]

EXAMPLE An example of the present invention will be described with reference to FIGS. 1, 2 and 3. FIG. 1 is a circuit diagram showing an embodiment of a digital filter according to the present invention, where 1 is a first analog low-pass filter, 2 is an analog / digital converter (hereinafter referred to as 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
Reference numeral 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 is an input signal (hereinafter referred to as fin), 16 is an output signal (hereinafter referred to as fout), 17 is a sampling frequency (hereinafter referred to as fs), and 18 is a first discretized sine wave frequency (hereinafter referred to as fosc1). , 19 is the second discretized sine wave frequency (hereinafter fosc2), 20 is the third discretized sine wave frequency (hereinafter fosc3), S1 is the first unnecessary signal, and S2 is A second unwanted signal, S3 is a first unwanted signal, S4 is a second unwanted signal, S5 is a first unwanted signal, and S6 is a third unwanted 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 reception sensitivity etc.

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

FIG. 2A shows a spectrum diagram when the fin 15 is A / D converted into a digital signal. In this embodiment, the first unnecessary signal S is added to the digitized input signal.
It is assumed that there are 1 and the second unnecessary signal S2, and the purpose thereof is to remove them.

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

As shown in FIGS. 2 (c), 2 (d) and 2 (e), in order to remove the second unwanted signal S2 located on the high frequency side of fin15, fin1 is used in the first digital multiplier.
The second undesired signal S2 in 5 generates fosc 118 from the first discretized sine wave oscillator 12 so that the portion of the second undesired signal S2 located in the stop band of the second digital low pass filter of FIG.
Shift fin15 so that becomes S4. At the same time, the first unnecessary signal S1 of the fin 15 is converted into 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
The second discretized sine wave oscillator 13 generates fosc 219 so that it is located in the stop 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 causes the third digital sine wave oscillator 14 to generate the fosc 320 in order to restore the original frequency band in the third digital multiplier. At this time, as shown in (i) of FIG.
15 is converted to the original frequency band, the converted fin15
Since the third unnecessary signal S6 is generated in the high frequency range of
As shown in (j) and (k), the third unnecessary signal S6 is filtered by the third digital low-pass filter in FIG.

Fin15 from which all unnecessary signals are removed is
The D / A converter 10 in FIG. 1 converts the analog signal.
The unnecessary component in the high frequency band 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 is removed.

[0024]

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

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

[Brief description of drawings]

FIG. 1 is a block diagram showing an 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]

 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 discretized sine wave signal 19 Second discretized sine wave signal 20 Third discretized sine wave signal 31 First analog low-pass filter 32 Analog / digital converter 33 Digital Low-pass filter 34 Digital high-pass filter 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 Second 1 unnecessary signal S4 2nd unnecessary signal S5 1st unnecessary signal S6 3rd unnecessary signal

Claims (1)

[Claims] 1. An analog / digital converter for digitizing an input analog signal, and a first for multiplying the input signal by the output from the analog / digital converter and the first discretized sine wave signal. A digital multiplier of the
A digital low-pass filter for filtering the high-frequency component of the input signal, and a second digital for multiplying the output from the digital low-pass filter by the second discretized sine wave signal. A multiplier and the second
, A digital high-pass filter for filtering the low-pass component of the input signal, and a third digital for multiplying the output from the digital high-pass filter by the third discretized sine wave signal. A multiplier and the third
And a digital / analog converter for analogizing an output signal from the digital multiplier of, to obtain an output analog signal by filtering a desired unnecessary signal.