JP3021093U - Digital filter - Google Patents

Abstract

(57) [Abstract] [Purpose] The characteristics of the digital filter can be changed by shifting the frequency band of the input signal digitized by the digital multiplier so that the unnecessary signal can be filtered by the digital filter and filtering only the unnecessary signal part. A digital filter capable of smoothly removing interference without being provided. [Configuration] A / D converter, multiple digital multipliers and discretized sine wave oscillator, digital bandpass filter, D / A
In a digital filter including a converter, a plurality of discretized sine wave oscillation signals are varied to remove a desired unnecessary signal.

Description

[Detailed description of the device]

[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 interfering wave may be mixed within its reception band. Then, in order to increase the reception sensitivity, the interference removal digital filter shown in Fig. 4 was inserted.

In the case of the digital signal for removing interference shown in FIG. 4, the high frequency unnecessary component of the input signal 27 is filtered by the first analog low-pass filter 21, and then analog / digital conversion (hereinafter referred to as A / D). The signal is converted into a digital signal by the device 22, the interfering wave is filtered by the digital band pass filter 23, and only the desired digital signal is passed through, and digital / analog conversion (hereinafter referred to as D / A conversion). The analog signal is returned by the device 24, 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 25 to obtain a demodulated signal 28 with interference removed.

In the above-mentioned digital bandpass filter 23, some filter coefficients having different cutoff frequencies are stored in the coefficient bank memory 26 in advance, and the operator demodulates from the interference removal digital filter shown in FIG. While listening to the signal 28, in order to obtain a filter characteristic such that interference is removed, a predetermined filter coefficient is fetched from the coefficient bank memory 26 by the selection signal 30 and the cutoff frequency of the digital bandpass filter 23 is changed. Interference was removed.

[0005]

In the conventional example shown in FIG. 4 described above, in order to smoothly change the digital bandpass filter 23, the operable band of the digital bandpass filter 23 is increased and the variation width of the cutoff frequency is increased. To reduce. However, the capacity of the coefficient bank memory becomes enormous, and it is difficult to change the cutoff frequency of the digital bandpass filter 23 in a time shorter than the sampling time 29 for digitizing the input signal 27.

Further, in the digital band pass filter 23, when each filter coefficient is varied, unnecessary noise is generated.

In view of the above-mentioned problems of the conventional example, in the present invention, it is unnecessary to shift the frequency band of the input signal digitized by the digital multiplier so that the unnecessary signal can be filtered by the preset digital filter. The objective is to obtain a digital filter that can smoothly remove interference without changing the characteristics of the digital filter by filtering only the signal part.

[0008]

In order to achieve such an object, an analog / digital converter that digitizes an input analog signal, and an output from the analog / digital converter as an input signal is used as the input signal. A first digital multiplier that multiplies the discretized sine wave signal with a digital bandpass filter that filters an unwanted signal of the input signal using the output from the first digital multiplier as an input signal; A second digital multiplier for multiplying the output from the digital bandpass filter by the discretized sine wave signal, and a digital / analog converter for analogizing the output signal from the second digital multiplier And a digital filter characterized by obtaining an output analog signal obtained by filtering a desired unwanted 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 the first digital low pass filter is provided. High-pass filtering with.

The digitized demodulated signal within the pass band of the preset digital band pass filter is multiplied by the discretized sine wave signal by the first digital multiplier to obtain the digitized demodulated signal. The discretized sine wave signal is varied so as to shift the unnecessary signal component out of the pass band of the digital band pass filter, and the unnecessary signal component of the digitized demodulated signal is filtered.

[0012] In order to restore the original frequency band after filtering the unnecessary signals in the high frequency band and the low frequency band of the digitized demodulated signal, the second digital multiplier uses the discretized sine wave signal. To multiply.

As a result of multiplication by the discretized sine wave signal, an unnecessary signal is generated in the high frequency band, so high frequency filtering is performed by the second 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 the output analog signal from which the desired unnecessary signal of the input analog signal is removed.

[0014]

Embodiment An embodiment 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, in which 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 digital band pass filter, 6 is a second digital multiplier, 7 is a digital low pass filter, and 8 is a digital / analog converter ( Hereinafter, referred to as a D / A converter), 9 is a second analog low-pass filter, and 10 is a first discretized sine wave oscillator. 11 is an input signal (hereinafter referred to as fin), 12 is an output signal (hereinafter referred to as fout), 12 is a sampling frequency (hereinafter referred to as fs), and 14 is a discretized sine wave frequency (hereinafter referred to as fosc). , S1, S2, S3, S4 and S5 are target signals, A1, A2 and A3 are first unwanted signals, and B1, B2 and B3 are second unwanted signals.

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 operation described below is performed to remove unnecessary signals mixed in the band. Improve the reception sensitivity.

In FIG. 1, fin 11 filters an unnecessary component in the high frequency band of fin 11 by a first analog low-pass filter 1 and digitizes and outputs it in A / D converter 2 at sampling frequency 13.

FIG. 2A shows a spectrum diagram when the fin 11 is A / D converted into a digital signal. In this embodiment, it is assumed that the digitized input signal has the first unnecessary signal S1 and the second unnecessary signal S2, and the purpose thereof is to remove them.

The digitized fin 11 is filtered by the first digital low-pass filter 3 as shown in FIG. 2 (b), and the high frequency components unnecessary for the processing of this embodiment are input to the first digital multiplier. .

As shown in FIGS. 2 (c), 2 (d) and 2 (e), the first undesired signal S 1 located on the low frequency side of the fin 11 and the second undesired signal S 2 located on the high frequency side. In order to eliminate the above, the portion of the first unnecessary signal S1 and the portion of the second unnecessary signal S2 in fin11 in the first digital multiplier are placed in the stop band of the digital band pass filter of FIG. The fosc 14 is generated from the discretized sine wave oscillator 10.

The fin 11 from which the two unnecessary signals in FIG. 2 (f) are removed causes the discretized sine wave oscillator 10 to generate fosc 14 in order to restore the original frequency band in the second digital multiplier. . At this time, as shown in (g) of FIG. 3, when fin11 is converted into the original frequency band, an unnecessary signal is generated in the high frequency part of the converted fin11, so that as shown in (h) of FIG. The second digital low-pass filter 7 shown in FIG. 1 filters the unnecessary signal in the high frequency band.

The fin 11 shown in FIG. 2 (i) from which all unnecessary signals have been removed is converted into an analog signal by the D / A converter 8 in FIG. The unnecessary component in the high frequency band generated at this time is filtered by the second analog low-pass filter 9 to obtain the output signal 12 from which the desired unnecessary signal is removed.

[0022]

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.

Further, in view of the recent development of the technology of the microcomputer and the like, various data processing and signal processing are executed at high speed, so that the response of the frequency conversion and the filtering by the digital filter of the present invention is extremely fast. Therefore, in practice, the digital filter of the present invention has an extremely excellent effect in eliminating interference in wireless communication devices.

[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 digital band-pass filter 6 2nd digital multiplier 7 2nd digital low-pass filter 8 digital / analog Converter 9 Second analog low-pass filter 10 Discretized sine wave oscillator 11 Input signal 12 Output signal 13 Sampling frequency 14 Discretized sine wave signal 21 First analog low-pass filter 22 Analog / digital converter 23 Digital band-pass filter 24 Digital / Analog converter 25 Second analog low-pass filter 26 Coefficient bank memory 27 Input signal 28 Output signal 29 Sampling time 30 Selection signal S1 First unnecessary signal S2 Second unnecessary signal

Claims (1)

[Scope of utility model registration request] 1. An analog / digital converter for digitizing an input analog signal, and a first digital multiplication for multiplying the input signal by an output from the analog / digital converter and the discretized sine wave signal. And a digital bandpass filter for filtering an unwanted signal of the input signal using the output from the first digital multiplier as an input signal, the output from the digital bandpass filter and the discretized sine wave signal. A second digital multiplier for multiplying
A digital filter comprising: a digital / analog converter for converting the output signal from the second digital multiplier into an analog signal to obtain an output analog signal by filtering a desired unnecessary signal.