JPS62279718A - Beat preventing device for on-vehicle radio receiver - Google Patents

Abstract

PURPOSE:To prevent the generation of a beat tone by controlling the switching frequency so that a harmonic being a noise source is not included in the tuning frequency band or coincident with the tuning frequency. CONSTITUTION:A switching pulse outputted from an oscillator 1 is inputted to a duty control circuit 2, controlled in response to a prescribed duty ratio and outputted to a transistor (TR) 3. The TR 3 is subjected to ON/OFF control and a DC motor 4 is subjected to duty control. The oscillator 1 is formed as a CR oscillator and oscillated at a frequency in response to a resistor 5 selected by a switching circuit 6. The movable iron piece 8 of the circuit 6 is subjected to switching control by using a switching signal from a microcomputer 7, a fluorescent display tube driving circuit 10 and the computer 7 detect the tunining frequency and the switching frequency is controlled so that the harmonics being a noise source are not included in the tuning frequency band and coincident with the tuning frequency. Thus, the generation of beat tone is prevented.

Description

Detailed description of the invention 3. Detailed description of the invention A. Industrial application field The present invention relates to a device for preventing beat interference caused by waves on AM radio, etc.

B. Prior art In recent years, various devices have been proposed that drive solenoid valves or DC motors mounted on vehicles by pulse switching using duty control (for example, Japanese Patent Application Laid-Open No. 11903-1983).
(See No. 4).

FIG. 7 schematically shows a DC motor control device as an example of this type of pulse switching device. In the control device shown in FIG. 7, a pulse outputted from a control circuit 101 causes a transistor 102 to be switched to control a DC motor 103.
The current flowing through the DC motor 103 is duty-controlled, thereby controlling the rotation speed of the DC motor 103.

This type of pulse switching equipment usually has a frequency of several tens of KHz.
Since it is necessary to switch transistors etc. with square wave pulses of ~ several hundred KHz, the harmonic components of the switching frequency are in the AM broadcast band (amplitude modulation medium wave band, 530 KHz)
~1600KHz) and is a powerful noise source. For example, Fig. 8 is a frequency spectrum diagram of the above-mentioned noise, and shows the results measured by a spectrum analyzer using the noise generated by the DC motor control device as the antenna terminal input voltage when the switching frequency is fKTIz. . Note that the vertical axis indicates the input voltage as 1 μV=OdB. As can be seen from FIG. 8, the noise spectrum when the switching frequency is fKHz appears as a line spectrum with intervals of fKHx.

The harmonics generated by the pulse switching equipment and appearing as a line spectrum interfere with the carrier wave of the receiving broadcasting station through direct and indirect coupling with the radio antenna, causing beat disturbance.

As a result, the quality of received sound is significantly impaired.

Such problems are unavoidable because no matter what frequency the switching frequency is set, as long as there are harmonics in the AM frequency band as shown in Figure 8, there will always be broadcast waves subject to the above beat interference. .

When one line spectrum is mixed in the tuning frequency band, the magnitude of the beat sound generated by interference shows a change as shown in FIG. 9 with respect to the frequency difference Δf between the mixed harmonic and the carrier wave. That is, from Fig. 9, the electric field is 60 dB.
When the magnitude of the interference wave Vu at the antenna terminal at μV/m is -1, 0, 0, 10, 20, and 30 dBμV, the frequency difference Δf is ±l0K1 (the loudness of the beat sound increases in the range of z). output) is t111! ! -22da(
It can be seen that the background noise level varies within a range of approximately 15 dB. Note that in FIG. 9, the vertical axis represents the magnitude of the beat sound as 0.5W = OdB.

Conventionally, in order to prevent such noise, measures have been taken such as inserting a filter into the power supply line of the pulse switching circuit or the wiring between the switching transistor and the motor, or applying a shield.

C1 Problem to be solved by the invention However, since the current flowing through the DC motor at maximum rotation becomes very large (more than IOA), the size of the filter coil becomes very large, and it is necessary to take measures with a shield. In some cases, if the distance of the shield becomes long, it becomes difficult to realize this in terms of cost.

Furthermore, there is also the problem that such measures often do not have sufficient effects.

An object of the present invention is to prevent beats in an in-vehicle radio receiver that solves the above-mentioned problems by controlling the switching frequency so that harmonics that are noise sources are not included in the tuning frequency band or match the tuning frequency. The goal is to provide equipment.

Means to solve D8 problem The basic principle of the present invention will be explained based on FIG.

FIG. 2 shows the carrier wave 60 of a receiving station in a radio receiver and the upper and lower side waves of an AM signal based on the frequency fc. 1
It shows the relationship between F61 and F62 and harmonics 63 to 67 which are interference waves from pulse switching equipment.

Here, the harmonics 63 and 64 are the n-th order of the frequency fs1 of a certain switching pulse.

The harmonic 65.67 is the (n-1) and (n+1)th of the frequency fs of another switching pulse, and the harmonic 66 is the n-th of the carrier wave. It matches the frequency fc. Further, in FIG. 2, the tuning frequency bandwidth WD of the AM signal is determined by the bandwidth from the lower limit frequency fLv of the sideband to the upper limit frequency fup of the upper sideband. Note that 68 indicates a passband by the intermediate frequency filter.

Now, as shown in FIG. 2, the n-th and (n+1)-th harmonics 63.64 of the switching pulse of frequency fs1 appear outside the tuning frequency bandwidth WD, or the nth of the switching pulse of frequency fs. The next harmonic 66 becomes the tuning frequency fc, which is the (n-1)th order.

The (n+1)th harmonic 65.67 is the tuning frequency band WD
By controlling the frequency of the switching pulse according to the tuning frequency, harmonics from the pulse switching equipment will not mix into both the upper and lower sidebands of the AM signal, no matter which broadcast station is received. , or the carrier wave, so that an audio signal without beat interference can be obtained.

Therefore, as shown in FIG. 1, the present invention includes a tuning frequency detection means 100 for detecting the tuning frequency of a receiving station, and a tuning frequency band in which the nth and (n+1)th harmonics of the switching pulse are detected. not to be included in, or
While matching the n-th harmonic with the tuning frequency (n-
1) Frequency control means 200 that controls the next and (n+1.) order harmonics so that they are not included in the tuning frequency band, and pulse generation means that outputs switching pulses based on the signal from the frequency control means 200. It consists of 300.

The E1 action tuning frequency detection means 100 detects the tuning frequency of the received AM (indication). According to the detected tuning frequency, the one frequency control means 200 detects the nth and (n+1)th harmonics of the switching pulse. control so that the waves are not included in the tuning frequency band, or so that the nth harmonic matches the tuning frequency and the (rrl)th and (n+1)th harmonics are not included in the tuning frequency band, The pulse generating means 300 outputs a switching pulse.Therefore, the audio signal does not include a beat sound.

F. Embodiment 1 First Embodiment The first embodiment will be described with reference to FIGS. 3 and 4.

In FIG. 1, a switching pulse output from an oscillator 1 is input to a duty control circuit 2, and as is well known, the pulse width is controlled according to a required duty ratio and output to a transistor 3. This switching pulse turns transistor 3 on and off, which causes D
The C motor 4 is duty-controlled. Here, the oscillator 1 is configured as a CR oscillator, and this CR oscillator 4 has n resistors 5-1.5-2...5-n, and has a frequency corresponding to the resistor 5 selected by the switching circuit 6. It is configured to oscillate and output a switching pulse. The switching circuit 6 is configured such that its movable contact piece 8 is switched and controlled by a switching signal from a microcomputer 7.

Frequency information is input to the microcomputer 7 from a fluorescent display tube drive circuit 10 for displaying the tuning frequency and the like on the fluorescent display tube 9. microcomputer 7
It is composed of well-known ROM, RAM, CPU, etc., and the ROM stores the control procedure shown in FIG. 4, and also stores n switching frequencies in advance. Then, under the control of the CPU, a switching frequency corresponding to the detected tuning frequency is selected, and a corresponding switching signal is output to the switching circuit 6.

In the above configuration, the fluorescent display tube drive circuit 10 and the microcomputer 7 constitute the tuning frequency detection means 100, the microcomputer 7 and the switching circuit 6 constitute the frequency control means 200, and the CR oscillator 1 constitutes the pulse generation means 300. configured. In FIG. 3, the CR oscillator 1° duty control circuit 2 and the switching circuit 6 constitute a control circuit 50 for a pulse switching device.

A fourth explanation of the operation of the first embodiment configured as described above is explained below.
This will be explained with reference to the control procedure shown in the figure.

The fluorescent display tube drive circuit 10 supplies the fluorescent display tube 9 and the microcomputer 7 with a fluorescent tube drive signal indicating the tuning frequency of the receiving station. The tuning frequency is displayed on the fluorescent display tube 9 by the drive signal. On the other hand, the microcomputer 7 executes the process shown in FIG. First, in step P1, a tuning frequency is detected from the input signal. Next, in step P2, a switching frequency in which neither the nth nor the (n+1)th harmonic is included in the tuning frequency band is selected from among the n switching frequencies stored in advance. For example, the tuning frequency and the nth and (n+1)
The next harmonic is stored in the form of a table in association with a switching frequency that is not included in the tuning frequency band, and the switching frequency is selected by looking up the table using the input tuning frequency. Alternatively, switching frequencies whose tuning frequency band does not include the nth and (n+1)th harmonics may be sequentially selected by calculation.

Then, in step P3, a switching signal is supplied to the switching circuit 6 in order to select the resistance necessary to oscillate a switching pulse of the selected frequency.

The movable contact piece 8 adjusts the desired resistance 1 according to the input switching signal.
5-1, and the CR oscillator 4 is a resistor] outputs a pulse with a frequency corresponding to 5-i. Then, the duty control circuit 2 processes the input switching pulse using an arithmetic circuit (not shown) and outputs a switching pulse having a desired pulse width to the transistor 3.

As described above, according to the first embodiment, since the n-th and (n+1)-th harmonics of the switching pulse are not included in the tuning frequency band, they do not interfere with the carrier wave and generation of beat sound can be prevented.

1. Second Embodiment A second embodiment will be described based on FIGS. 5 and 6. Note that the same parts as in FIG. 3 are given the same reference numerals.

The AM signal is input to a comparison input terminal of a phase comparison circuit (PLL circuit) 21, and the output of the 1-phase comparison circuit 21 is input to a voltage controlled oscillator 23 through a low-pass filter 22. The output of the voltage controlled oscillator 23 is input to the compared input terminal of the frequency dividing circuit, that is, the programmable divider 24 and the phase comparator circuit 21, and
The output is input to the control circuit 25 as a switching pulse of a predetermined frequency.

Then, the control circuit 25 generates a switching pulse whose pulse width corresponds to a predetermined duty ratio, which causes the transistor 3 to
is turned on and off to control the DC motor 4.

As in the first embodiment, frequency information indicating the tuning frequency is input to the microcomputer 7 from the fluorescent display tube drive circuit 10. The microcomputer 7 detects the tuning frequency fc according to the control procedure shown in FIG. is configured to output to . The optimal switching frequency is
■Stable oscillation is obtained for duty control, ■Low switching loss, and ■Below the audible frequency band.
In order to satisfy this condition, generally 20 to 30K
It is set within the range of Hz.

In the above configuration, the fluorescent tube drive circuit 10 and the microcomputer 7 constitute the tuning frequency detection means 100, the phase comparison circuit 21. Low pass filter 22, voltage controlled oscillator 23. A frequency control means 200 is configured by the programmable divider 24 and the microcomputer 7, and a phase comparison circuit 21. Low pass filter 22. The voltage controlled oscillator 23 and the programmable divider 24 constitute a pulse generating means 300.

The operation of the second embodiment configured in this way will be explained in the sixth section.
This will be explained with reference to the control procedure shown in the figure.

A fluorescent tube drive signal indicating the tuning frequency of the receiving station is sent to the drive circuit 1.
When the signal is input from 0 to the microcomputer 7, the tuning frequency is first detected from the input signal in the procedure pH. Then in step P1.2.

The frequency division ratio N is determined based on the above equation (1). That is,
As mentioned above, the frequency fs is preferably 20 to 30K[[z, so fs is set sequentially from 20 to 20.1.20.2 and 3.
Equation (1) is calculated by incrementing the frequency up to 0 by 0.1, and in step P3, N, the quotient of which is a natural number, is output to the programmable divider 24 as a frequency division ratio.

On the other hand, the AM signal (frequency fc) is used as the compared input, and the output signal (hereinafter referred to as the VCO signal and its frequency is referred to as fv) from the voltage controlled oscillator 23 is used as the phase comparison input.
The phase comparator circuit 21 to which is inputted outputs a voltage according to the phase difference between the inputted AM signal and vC○ signal. This voltage signal is integrated by a low-pass filter 22 and input to a voltage controlled oscillator 23, which outputs a VCO signal with a frequency corresponding to the input voltage to a phase comparator circuit 21. Therefore, the vCO signal becomes a signal of the same frequency that is synchronized with the AM signal.

The vCO signal obtained in this way is input to the programmable divider 24 and divided by the frequency division ratio N set by the microcomputer 7, so that f s == f v/N= f c/N
A switching pulse with a frequency expressed by =(2) is obtained. This switching pulse is then processed in a well-known manner by the control circuit 25 into a switching pulse having a desired duty width, and the transistor 2 is controlled to be turned on or off in accordance with the pulse.

As described above, according to the second embodiment, the frequency of the n-th harmonic of the switching pulse matches the frequency of the carrier wave,
Also, normally, the tuning frequency band WO shown in Figure 2 is 16K.
Since the harmonics of the (n-1)th order and the t(n''i)th order appear outside the band WD, beat interference is prevented.

In addition to strong electric fields, even in weak electric fields where the received sound quality can be ensured at the lowest level, the level of harmonics that become interference waves is sufficiently small compared to the carrier wave, so the sound quality will not be impaired even if the frequencies are the same. In addition, since the frequency division ratio N is variable so that the frequency of the switching pulse becomes the optimum value according to the tuning frequency, it is possible to match the harmonics that become interference waves even when combined with the carrier waves of all AM broadcasting stations. , beat disturbance is reliably prevented.

In addition, when calculating the frequency division ratio N, calculate the frequency division ratio N for various tuning frequencies based on equation (1),
This may be stored in the microcomputer 7 as a table of tuning frequency fc - frequency division ratio N, and the frequency division ratio N may be determined by referring to the table according to the detected tuning frequency. ”G1 Effect of the Invention According to the present invention, the frequency of the switching pulse is controlled according to the tuning frequency so that the nth and (n+1)th harmonics of the switching pulse are not included in the tuning frequency band, or , the nth harmonic matches the tuning frequency, and the (n-1)th and (n+1)th harmonics are not included in the tuning frequency band, so the harmonics of the switching pulse do not interfere with the carrier wave. To reliably prevent the generation of beat sounds from an in-vehicle radio receiver.

[Brief explanation of the drawing]

Fig. 1 is a diagram corresponding to the claims of the present invention, Fig. 2 is a diagram showing the frequency relationship between the carrier wave, upper and lower sidebands, and harmonics of noise;
3 and 5 are block diagrams respectively showing the first and second embodiments of the beat prevention device of the present invention, and FIGS. 4 and 6 are block diagrams showing an example of a processing procedure by a microcomputer. Flowcharts of each example,
Figure 7 is a configuration diagram of an example of a DC motor control device, Figure 8 is a frequency spectrum diagram of noise, and Figure 9 is a diagram showing the relationship between the frequency difference between a carrier wave and harmonics and the magnitude of beat sound generated by interference. It is °. 100: Tuning frequency detection means 200: Frequency control means 300: Pulse generation means Applicant: Nissan Motor Co., Ltd. Representative Patent Attorney Fuyuki Nagai Figure 1 Figure 2 Figure 7 Figure 8 s) ward ■ sect

Claims (1)

[Claims] Tuning frequency detection means for detecting the tuning frequency of the receiving station;
The n-th and (n+1)-th harmonics of the switching pulse are not included in the tuning frequency band detected by the tuning frequency detection means, or the n-th harmonics are made to match the tuning frequency, and ( Frequency control means for controlling the n-1)th and (n+1)th order harmonics so that they are not included in the band of the tuned frequency, and pulse generation means for outputting switching pulses based on the signal from the frequency control means. A beat prevention device for an in-vehicle radio receiver, comprising: