JPS61150408A - Digital filter - Google Patents

Abstract

PURPOSE:To obtain two outputs in a small circuit scale by securing the partial share between a low band-pass filter and a band-pass filter. CONSTITUTION:An input signal is converted into a digital signal by an A/D converter 1. A delay element 5a receives the delay of a single unit time by the signal of a sampling signal generator 6 and is used as the input of a delay element 5b after undergoing the four rules of arithmetic. The inputs of both elements 5a and 5b are turned as they are into outputs and delivered through D/A converters 2a and 2b synchronously with the signal of the generator 6. These outputs of converters 2a(D/A1) and 2b(D/A2) are used as the outputs of a low band-pass filter and a band-pass filter respectively. Thus four multipliers and three addition/subtraction units are used. This decreases greatly the number of subtractors and simplifies the circuit constitution with high economical properties.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital filter that converts an input signal into a digital signal and determines its passband characteristics through real-time logic processing. In particular, it relates to quadratic low-pass and band-pass filters constructed based on state variable methods.

INDUSTRIAL APPLICATION This invention is utilized for a communication device.

〔overview〕

In a digital filter that performs real-time logic processing, converts the output into an analog signal, and outputs it, two outputs can be generated in a small circuit scale by providing a low-pass filter and a band-pass filter as part of the circuit. It is something that will be realized.

[Conventional technology]

Based on the state variable method (a quadratic filter is generally expressed by the first equation attached to the example section). The transfer function of the digital filter is obtained by applying an appropriate S-Z transformation (e.g., bilinear transformation, matching 2 transformation, etc.) to the transfer function of Get the form of the expression.

[Problem that the invention seeks to solve]

However, when trying to obtain two outputs with both low-pass and band-pass characteristics using the conventional method described above,
In the first equation, matrices C and D are not necessarily unit matrices and dedicated matrices, respectively. Therefore, when processing the first equation above, the number of multipliers and adders/subtractors required for the calculation is as follows: 12 multipliers and 4 adders/subtractors are required as shown in the conventional example shown in FIG. Finally, there were problems with the complexity of the circuit configuration and economic efficiency.

The present invention was made in order to solve the above-mentioned problems, and an object of the present invention is to provide a low-pass/band-pass digital filter in which the number of multipliers and adders/subtractors in an arithmetic unit is significantly reduced. .

[Means for solving problems]

The low-pass or band-pass type digital filter of the present invention is capable of outputting two types of signals with low-pass and band-pass characteristics through real-time numerical processing in response to an input signal of a specific frequency. Features. Furthermore, it is desirable that the specific frequency is an audible frequency.

[Effect]

According to the first and second equations attached to the embodiment section, the present invention makes the matrix rcJ an "identity matrix" and the matrix rDJ a "dedicated matrix," thereby obtaining a low-pass signal from the state variables x, (n). A bandpass characteristic arises from x,(n).

By adjusting the "unit matrix" and "dedicated matrix" using the attached second equation, the matrix rBJ is determined, and the number of multipliers and adders/subtracters provided focusing on the relationship with the initial response of this filter is reduced compared to the conventional example. It will show the same performance with a significantly smaller number.

〔Example〕

The present invention will be explained with reference to an embodiment of the apparatus shown in FIG. 1 attached hereto. The input signal is sent to an adder/subtractor 4 via an analog-to-digital converter 1.
Enter a and 4C. The output of the adder/subtractor 4a is input to the delay element 5a, and the output of the delay element 5a is input to the adder/subtractor 4a via the multiplier 3a, and is also manually input to the adder/subtractor 4C and the digital/analog converter 2a. . This 2a output is a low-pass filter output #l. The output of the adder/subtractor 4C is input to the adder/subtracter 4b via the multiplier 3b. The output of the adder/subtractor 4b is sent to the delay element 5b.
Enter. The output of the delay element 5b is sent to the digital converter 2.
b, are input to multiplier 3C and multiplier 3d, respectively.

The output of the multiplier 3C is input to the adder/subtracter 4a. The output of the multiplier 3d is input to the adder/subtracter 4b. The output of the digital-to-analog converter 2b is the output #2 of the bandpass filter. The output of the sampling signal generator 6 is input to the analog-to-digital converter 1 and the digital-to-analog converters 2a and 2b and delay elements 5a and 5b, respectively.

Next, the operation of the device of the present invention will be described. The input signal is converted into a digital signal by an analog-to-digital converter 1. The delay element 5a applies a two-cycle delay to the signal from the sampling signal generator 6, and after being subjected to addition, subtraction, and multiplication processing, becomes the force of the delay element 5b. In the present invention, the inputs of the delay elements 5a and 5b become outputs as they are, and are outputted through the digital-to-analog converters 2a and 2b in synchronization with the signal from the sampling signal generator 6. Of the digital-to-analog converters 2a and 2b, 2a (D/Al) is the output of a low-pass filter, and 2b (D/A2) is the output of the band-pass filter.

In the present invention, the number of multipliers and adders/subtractors can be significantly reduced by adjusting the "unit matrix" and "dedicated matrix" using the first and second equations shown below. 1st
The formula is a general formula for a digital filter based on the state variable method,
The second equation is a state variable representation of a low-pass or band-pass filter according to the invention.

First equation; Here, u (n) is the human power at time n, V + (n), y2
(n) is the output; x+(n), x-<n) is the state variable,"
ij, C1js b,, di (i, j=1.2) are constants determined so that y+(n) and yz(n) have low-pass and band-pass characteristics, respectively.

Second equation; Here u (n) is the input at time n, Xl (n),'
xz(n) is the state variable, xl(n) is the low pass,
x2(n) is the output of a filter with bandpass characteristics.

r cos θ and r sin θ are constants, and the filter cutoff frequency fo, quality factor Q, and sampling interval T have the following relationship: r = e xp (-πf, T/Q) θ = JT = be.

〔Effect of the invention〕

Comparing the present invention with a conventional device, the conventional device requires 12 multipliers and 4 adders/subtractors, whereas the present invention consists of 4 multipliers and 3 adders/subtractors. The number of arithmetic units is greatly reduced, which has the effect of simplifying the circuit configuration and improving economy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of a conventional device. 1...Analog-digital converter, 2a, 2b...
- Digital-analog converter, 3a to 31... Multiplier, 4a to 4d... Addition/subtraction device, 5a, 5b... Delay element, 6... Sampling signal generator.

Claims (2)

[Claims] (1) Analog converting input signal to digital signal
a digital converter; circuit means for logically processing this digital signal in real time; a digital-to-analog converter for converting the output of this circuit means into an analog signal; and an output to which the output of this digital-to-analog converter is connected. In the digital filter having a terminal, the circuit means outputs a first output signal having a low-pass characteristic and a second output signal having a band-pass characteristic in response to an input signal in a characteristic frequency range. A digital filter, characterized in that the digital-to-analog converter and the output terminal are provided separately via the first output signal and the second output signal. (2) The digital filter according to claim (1), wherein the specific frequency range is an audible frequency range.