JPH0345021A - Communication equipment - Google Patents

Abstract

PURPOSE:To evade the generation of beat, and to eliminate the need for restriction of layout or strict shielding by shifting an oscillating frequency of a crystal oscillation circuit supplying a clock signal to a microcomputer in response to a communication channel, and parting the high frequency component of the clock signal from the communication channel. CONSTITUTION:An input signal from a high frequency signal input terminal 1 is mixed with a local oscillation signal from a local oscillation circuit 6 at a mixer circuit 2, the frequency is selected via an IF circuit 3 and a desired signal is extracted at a low frequency signal output terminal 5 via a low frequency circuit 4. The output frequency of the local oscillation circuit 6 is controlled by a microcomputer 7. In such a case, the clock frequency supplied to a CPU in the microcomputer 7 is shifted in response to the communication channel to part the harmonic component of the clock signal from the frequency component use for the communication channel. Thus, the generation of beat is waded, and the limit in the layout or strict shield is waded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a communication device in which communication channel switching is controlled by a microcomputer.

(Prior Art) Generally, in a communication device capable of receiving a plurality of channels, switching of communication channels is controlled by a microcomputer.

FIG. 3 shows a schematic configuration of a conventional microcomputer in this type of communication device, which includes a central processing unit (hereinafter referred to as CPU) 21, capacitors 22, 23, crystal oscillator 24, resistor 25, and inverter amplifier 26. It is equipped with a crystal oscillation circuit consisting of. This crystal oscillation circuit oscillates at an oscillation frequency according to constants of the capacitor, crystal oscillator, resistor, etc., and supplies a clock signal of this frequency to the CPU 21. This causes the CPU 21 to operate.

However, in such communication devices, the harmonic components of the clock signal frequency fall within the reception band and coincide with one or more of the communication frequencies, causing the desired frequency to be lost. When receiving a communication channel, beats may occur and the distortion rate of the received signal may worsen.

For this reason, in the past, in order to prevent harmonics of the clock signal frequency from entering communication equipment, it was necessary to create a layout between devices, which required strict shielding, etc. There have been problems such as restrictions on the equipment and an increase in the weight of the equipment.

This invention was made in view of the above-mentioned problems,
The purpose is to provide a communication device that avoids the occurrence of beats through electrical measures and does not require layout restrictions or strict shielding.

[Structure of the invention]

(Means for solving the problem) In order to achieve the above object, the present invention provides a communication device in which communication channel switching is controlled by a microcomputer, in which a clock signal used in the microcomputer is supplied. The invention is characterized in that it includes means for shifting the oscillation frequency of an oscillation circuit according to a communication channel, and the harmonic components of the clock signal are separated from the communication channel.

(Function) According to this configuration, since the harmonic components of the clock signal are kept away from the communication channel, it is possible to avoid the occurrence of beats, which eliminates the need for layout constraints and strict shielding. It can be tightened.

(Embodiment) FIG. 1 is a block diagram schematically showing the configuration of a main circuit of a communication device capable of receiving a plurality of channels.

In the figure, a human input signal from a high frequency signal input terminal 1 is mixed with a local frequency signal from a local oscillator circuit 6 in a mixer circuit 2, and then frequency selection is performed by passing through an IF open circuit. By passing through the frequency circuit 4, a desired signal is extracted to the low frequency signal output terminal 5.

The local oscillator circuit 6 is generally a PLL (Phase L).
A frequency synthesizer using a locked loop) circuit is used.

The output frequency of this frequency synthesizer is controlled by a microcomputer 7.

Here, an explanation will be given using the frequencies of car telephones in the United States as an example. The radio reception frequency for car phones in the United States is 869.04.
~893.97 MHz, and reception channels are set every 30 KHz.

On the other hand, in the microcomputer of this type of device, C
The clock frequency supplied to the PU is 512MHz, 1
Frequency is often 0.24MHz.

Here, taking a clock frequency of 1.0.24 MHz as an example, if the frequency deviation of the clock oscillation circuit is ±0, the harmonic of 87 times 10.24 MHz is 890.88.
MHz, which corresponds to the 696th channel of the receiving frequency (current American car telephones have 870°03 MHz as the first channel), and when the desired signal is received, a beat is generated.

Furthermore, if there is a frequency deviation in the clock oscillation circuit,
There is a possibility of causing interference not only to the above-mentioned channels but also to adjacent channels. For example, if an oscillation circuit with a frequency deviation of ±30 ppm is used, 8
The range of the 7th harmonic is 890.853MHz to 890.85MHz.
907MHz, and not only the 696th channel but also the 695th channel
CH (890, 85MHz) and 697th CH (890, 85MHz)
There is also a possibility of beat generation at 91 MHz).

Therefore, in the present invention, the above-described beat generation is prevented as follows.

For the CPU used in the microcomputer of this type of device, the frequency deviation of the clock signal is specified in relation to the data transmission speed, and in the example of an American car telephone, it is set to ±1100 pp.

Therefore, in this implementation column, the frequency of the clock signal is shifted to the + side by 50 ppm. In this case, the frequency deviation is +80 to +20 ppm, and the harmonic frequency is 890.951 MHz to 890.898 MHz, so there is a possibility that a beat will occur in the 696th CH to 699th CH.

However, when attempting to receive any of the 696th CH to 699th CH, the clock frequency is further switched to one side by 1100 ppm (50 ppm on one side of the nominal frequency) under the control of the microcomputer.

Then, the deviation of the clock frequency is -80 to -20 ppm
Therefore, the harmonic frequency is 890.809MHz ~ 89
0.86'2MHz, which is the closest frequency to the 696th
Since there is a distance of 18 KHz from the CH, the possibility of beat generation can be avoided.

Note that the band per channel of car telephones in the United States is ±15 KHz, and we believe that if interference waves fall within this band, there is a possibility that some kind of beat may occur.

FIG. 2 is a block diagram showing an embodiment of the microcomputer in the communication device shown in FIG. 1. In FIG. 2, the same reference numerals are given to parts that perform the same functions as those of the conventional microcomputer shown in FIG. 3 for convenience of explanation.

In this embodiment, a resistor 11, a variable capacitance diode 12, and a capacitor 13 are added to the conventional microcomputer shown in FIG. The voltage is applied to the variable capacitance diode 12. The variable capacitance diode 12 has different capacitances when a voltage of 5V is applied and when a voltage of OV is applied. This changes the constant of the crystal oscillation circuit, making it possible to change the frequency of the clock signal.

Now, in normal channel reception, variable capacitance diode 1
Set the applied voltage of step 2 to 5V.

Then, the frequency of the clock signal becomes 50 ppm on the plus side of the nominal frequency based on the constant of the crystal oscillation circuit according to the capacitance value of the variable capacitance diode 12 when a voltage of 5V is applied.

In this state, as described above, a beat will not occur when a desired communication channel is received, except when receiving a specific channel where a beat occurs, that is, the 696th CH to the 699th CH.

Next, when receiving the 696th CH to 699th CH in which a beat occurs, the voltage applied to the variable capacitance diode 12 is set to OV.

Then, based on the constant of the crystal oscillator circuit that corresponds to the capacitance value of the variable capacitance diode 12 when the applied voltage drops from 5V to 0V, the frequency of the clock signal changes to 1100V to one side.
pp (50 ppm on either side of the nominal frequency).

In this state, the deviation of the frequency of the clock signal is −
Since it is 80 to -20 ppm, the harmonic frequency is 89
The frequency is 0.809 MHz to 890.862 MHz, and even with the nearest 696th frequency, it is 18KH.
It is possible to obtain a frequency difference of as much as z, and it is possible to reliably avoid the occurrence of beats.

As described above, according to the device of this embodiment, the oscillation frequency of the crystal oscillation circuit that supplies the clock signal to the CPU 21 of the microcomputer is shifted in accordance with the communication channel, and the high frequency component of the clock signal is separated from the communication channel. This makes it possible to avoid the occurrence of beats, thereby making it possible to provide a communication device that does not require layout restrictions or strict shielding.

In the above embodiment, the case of a car phone in the United States was explained as an example, but the amount of frequency shift varies depending on various communication devices, and in short, no beat occurs between harmonics of the clock oscillation frequency and the receiving band. You can set it like this.

〔Effect of the invention〕

As is clear from the above explanation, 1. According to the present invention, it is possible to avoid the occurrence of electrical beats, so there is no need for restrictions on the internal layout of the device or the need for strict shielding. This makes it possible to reduce the size and weight of this type of device.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing the configuration of a receiving section of a communication device, FIG. 2 is a diagram showing a microcomputer to which an embodiment of the present invention is applied, and FIG. 3 is a circuit diagram showing the configuration of a conventional device. It is. 1...High frequency signal input terminal, 2...Mixer circuit,
3... JF open circuit 4... Low frequency circuit, 5... Low frequency signal output terminal, 6... Local oscillator circuit, 7... Microcomputer, 11.25... Resistor, 12. ...Variable capacitance diode, 13,22.23...Capacitor,
21...Central processing unit, 24...Crystal resonator, 26
...Inverter amplifier

Claims (1)

[Claims] A communication device in which communication channel switching is controlled by a microcomputer, comprising means for shifting the oscillation frequency of an oscillation circuit that supplies a clock signal used by the microcomputer according to the communication channel, A communication device characterized in that harmonic components are separated from the communication channel.