JPH11208387A - On-vehicle digital communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an on-vehicle digital communication system which can eliminate influence by a noise component generated inside a vehicle. SOLUTION: In an on-vehicle digital communication system to input to a receiver 9 through a filter 5 in order to perform communication transmission of a digital data from a transmitter 8 by a high frequency using a DC power line L, the system is provided with a generation means 1 to 4 generating a sampling frequency signal f based on a low frequency noise component generated periodically in the inside of a vehicle, an A/D converter means 61 to be inputted with an output of the filter, a digital filter means 6A to be inputted with an output of the A/D converter means, a D/A converter means 65 to be inputted with an output of the digital filter means, and a subtraction means 66 subtracting an output of the D/A converter means from the output of the filter and inputting it to the receiver.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital communication system for vehicles.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 10, an in-vehicle digital communication system in which digital data communication transmission from a transmitter 8 to a receiver 9 is performed at a high frequency using an in-vehicle DC power line L is known. is there. For example, when a plurality of audio devices such as an amplifier and a CD player constitute an in-vehicle audio set, the devices are commonly connected to a battery by a power cord and connected to each other by connection lines such as an audio code and a control code. And exchanges signals. However, as the number of devices increases, the number of connection lines also increases.Therefore, each device omits the connection lines except that it is commonly connected to the battery with a power cord, and by mounting the digital communication system described above, each device has a mutual connection. Signals are being exchanged.

In such a vehicle-mounted digital communication system, the receiver 9 receives the digital data converted to high frequency (hereinafter, referred to as high-frequency digital data), so that the receiver 9 matches the frequency band of the high-frequency digital data. BPF5 was used. The BPF 5 cuts high frequency vehicle noise components other than high frequency digital data.

[0004]

However, at the receiver side, B
When the PF is used alone, a noise component that is periodically generated inside the vehicle (for example, an ignition noise or an engine noise that is generated inside the vehicle and rides on the power supply line of the battery 7). Noise components (for example, engine noise) in the same band as the pass band of the BPF cannot be removed. This noise component may be input in addition to the data digital data. Therefore, normal data communication may not be performed.

[0005] It is an object of the present invention to provide a vehicle-mounted digital communication system which solves the above-mentioned conventional problems.

[0006]

According to a first aspect of the present invention, there is provided a digital communication system for a vehicle, which uses a DC power line to transmit digital data from a transmitter at a high frequency. In a vehicle-mounted digital communication system for inputting a signal to a receiver via a filter having a frequency band through which the high-frequency digital data passes, sampling for generating a sampling frequency signal based on a low-frequency noise component periodically generated inside the vehicle Frequency signal generating means, A / D converting means to which the output of the filter is input and which operates at the sampling frequency from the sampling frequency signal generating means, and digital filter means to which the output of the A / D converting means is input D / A conversion means to which an output of the digital filter means is inputted, and an output of the filter By subtracting the output of al the D / A converting means, characterized in that a subtraction means for input to the receiver.

Further, according to a second aspect of the present invention, there is provided a vehicle-mounted digital communication system which uses a DC power line to perform communication transmission of digital data from a transmitter at a high frequency. In a vehicle-mounted digital communication system input to a receiver through a filter having a frequency band through which data passes, a reference signal creation circuit that creates a reference signal based on a low-frequency noise component that periodically occurs inside the vehicle, A PLL circuit that uses a signal from the reference signal generating unit as a reference signal, an A / D converter to which an oscillation output of the PLL circuit is used as a sampling frequency, and an output of the filter, and an output of the A / D converter. A digital filter to be input, a D / A converter to which an output of the digital filter is input,
A subtractor for subtracting the output of the D / A converter from the output of the filter and inputting the result to the receiver.

According to a second aspect of the present invention, in the vehicle digital communication system according to the second aspect, the reference signal generating circuit periodically generates the reference signal inside the vehicle. And generating a reference signal based on the alternator noise component.

[0009]

FIG. 1 is a block diagram showing an embodiment of a digital communication system for a vehicle according to the present invention.
In FIG. 1, 1 is an LPF (low-pass filter), 2 is a reference signal generation circuit, 3 is a frequency detection circuit, and 4 is a PLL.
(Phase Locked Loop) circuit, 5 is a BPF (Band Pass Filter), 6 is a noise removal circuit, 7 is a battery,
8 is a transmitter and 9 is a receiver.

As shown in FIG. 2, the LPF 1 includes a noise component generated inside the vehicle and on the power supply line of the battery 7 (for example, an ignition noise generated at any time, an engine noise generated periodically and a Alternator noise (about 1 KHz to 10 KHz in band,
It depends on the engine speed of the vehicle. ) Etc.)
Extract only alternator noise. The reference signal generation circuit 2 has a configuration example shown in FIG. 3, and includes a comparator A1 to which a reference voltage (b) is input to a minus input side from a connection point of the resistors R2 and R3. The alternator noise (a) extracted by the LPF 1 is input to the plus input side of the comparator A1 to create a reference signal (c) shown in FIG. This reference signal (c) is input to the phase comparator 41 of the PLL circuit 4 as a reference signal.

FIG. 5 shows an example of the structure of the frequency detection circuit 3. The reference signal from the reference signal generation circuit 2 is connected to the plus input side of each of the comparators A2, A3 and A4 by a resistor R4.
And a reference voltage (1) ′ different from each other depending on the voltage division of the resistors R5 to R8.
(2) 'and (3)' are input. Reference signal creation circuit 2
Changes depending on the engine speed.
For example, when the rotation speed increases, as shown in FIG. 6, the reference signal changes in the order of (1) → (2) → (3) so that the period gradually becomes shorter.

Therefore, the DC voltage levels when the reference signals shown in FIGS. 6 (1), (2) and (3) are rectified are respectively (1) ', (2)' and (3) 'in FIG. , The comparison reference voltages input to the minus inputs of the comparators A2, A3 and A4 respectively correspond to the DC voltage levels (1) ', (2)', (3) ′.

The comparators A2, A3 and A4 output an "L" level signal when the integrated reference signal voltage level supplied to the plus input side does not exceed the comparison reference voltage, and outputs an "L" level signal. In the case of a level, an "H" level signal is output. Table 1 shows input reference signals (FIG. 6).
Each comparator A for (1), (2) and (3))
2, a truth table showing the outputs (a), (b) and (c) of A3 and A4. In this table, the "H" level is 5 volts and the "L" level is 0 volts.

[0014]

[Table 1]

The state of the reference signal frequency can be confirmed by the combination of "H" and "L". (Note that
Although three comparators are used here, the number may be increased to increase the resolution. )

The PLL circuit 4 comprises a phase comparator 41, a loop filter 42, a VCO (voltage controlled oscillator) 43, a frequency divider 44, and a multiplexer 45. PL
The L circuit 4 generates a digital circuit clock synchronized with the alternator noise of the vehicle. The oscillation output (fout) generated by the VCO 43 is divided into 1 / N by the frequency divider 44 to provide several types (for example, fout /
N1 ≠ fout / N2 ≠ fout / N3) and input to the multiplexer 45. The output of the multiplexer 45 is switched by the output of the frequency detection circuit 3, outputs (fout / N) that matches the reference signal, and is input to the phase comparator 41. By synchronizing with the reference signal from the reference signal generation circuit 2 by the PLL circuit 4, an output having a frequency N times higher than that of the reference signal is obtained, and a clock for the digital circuit synchronized with the alternator noise of the vehicle is obtained.

The BPF 5 is the BP used in the prior art.
The same as F may be used to extract high frequency digital data. FIG. 8 shows an example of input and output waveforms of the BPF 5.

The noise removal circuit 6 includes an A / D converter 6
1, adder 62, one-cycle delay memory 63,
It comprises an adder 64, a D / A converter 65, a subtractor 66, and a reset signal generation circuit 67.

The high-frequency digital data extracted by the BPF 5 is subjected to A / D conversion by the A / D converter 61 of the noise elimination circuit 6.
Is converted. The oscillation output (fout) of the VCO 43 of the PLL circuit 4 is supplied to the A / D converter 61 to determine a sampling frequency at the time of A / D conversion. Next, an adder 62 and a one-cycle delay memory 63 for delaying the A / D-converted data by one cycle.
And the adder 64, the digital filter 6A for noise removal is configured. (Here, the cycle is a cycle of oil-noiter noise.) In the one-cycle delay memory 63, the PLL circuit 4 is used to take each timing at the time of writing (W) and reading (R).
The oscillation output (fout) of the VCO 43 is supplied.

The reset pulse used in the one-cycle delay memory 63 is generated by the reset signal generation circuit 67 using the signal from the frequency divider 44 in accordance with the falling timing of the reference signal. Here, high-frequency digital data not synchronized with the reference signal is treated as random noise. Digital data treated as random noise is averaged by the digital filter 6A.

Further, since the engine noise synchronized with the reference signal is constantly generated every cycle, it is output from the digital filter 6A as it is. The engine noise output from the digital filter 6A is D / A converted by the D / A converter 65 (the oscillation output (fou) of the VCO 43 of the PLL circuit 4 is supplied to the D / A converter 65.
t) is supplied to determine the sampling frequency at the time of D / A conversion), and is subtracted by subtracting the original data extracted from the BPF 5 by the subtractor 66, and only high-frequency digital data is extracted. 9 will be supplied. FIG. 9 shows an example of a signal waveform of each unit in the operation described above.

As described above, (1) the noise elimination circuit can separate the high frequency digital data and the periodically generated engine noise in the same band, so that the influence of the engine noise on the communication is small. Become. (2) Since the alternator noise generated from the vehicle is used as the reference signal of the PLL, the clock signal of the digital circuit always follows the rotation speed of the engine.
(The rotation of the engine and the clock signal are synchronized.)

[0023]

According to the present invention, the influence of noise components generated inside the vehicle can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an in-vehicle digital communication system according to the present invention.

FIG. 2 is a schematic diagram showing a state of a signal on a DC power supply line.

FIG. 3 is a circuit diagram illustrating a configuration example of a reference signal generation circuit.

FIG. 4 is a waveform diagram of each part of the reference signal generation circuit of FIG. 3;

FIG. 5 is a circuit diagram illustrating a configuration example of a frequency detection circuit.

FIGS. 6 (1), (2) and (3) show changes in the reference signal of the reference signal generation circuit.

7 (1) ', (2)' and (3) 'show DC voltage levels when the reference signals shown in (1), (2) and (3) of FIG. 6 are rectified.

FIG. 8 shows input / output waveforms of a BPF.

9 (a) to 9 (f) show signal waveforms at various parts in the block diagram of FIG. 1;

FIG. 10 shows a configuration example of a conventional in-vehicle digital communication system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 LPF 2 reference signal creation circuit 3 frequency detection circuit 4 PLL circuit 5 BPF 6 noise removal circuit 6A digital filter 7 battery 8 transmitter 9 receiver 41 phase comparator 42 loop filter 43 VCO 44 frequency divider 45 multiplexer 61 A / D Converter 62 Adder 63 1-cycle delay memory 64 Adder 65 D / A converter 66 Subtractor 67 Reset signal generation circuit

Claims (3)

[Claims] 1. An in-vehicle digital device that uses a DC power line to transmit digital data at a high frequency from a transmitter and transmits the digital data to a receiver via a filter having a frequency band through which the high-frequency digital data passes. In a communication system, a sampling frequency signal generating means for generating a sampling frequency signal based on a low frequency noise component periodically generated inside a vehicle; an output of the filter being input; and a sampling frequency from the sampling frequency signal generating means. A that works with
/ D conversion means, digital filter means to which the output of the A / D conversion means is input, D / A conversion means to which the output of the digital filter means is input, and D / A conversion from the output of the filter Subtracting means for subtracting the output of the means and inputting the result to the receiver. 2. An in-vehicle digital device which uses a DC power line to transmit digital data at a high frequency from a transmitter and transmits the digital data to a receiver via a filter having a frequency band through which the high-frequency digital data passes. In a communication system, a reference signal creation circuit for creating a reference signal based on a low-frequency noise component periodically generated inside a vehicle, and a PL using a signal from the reference signal creation means as a reference signal
An L circuit, and an oscillation output of the PLL circuit as a sampling frequency;
An A / D converter to which an output of the filter is input; a digital filter to which an output of the A / D converter is input; a D / A converter to which an output of the digital filter is input; And a subtracter for subtracting the output of the D / A converter and inputting the result to the receiver. 3. The on-vehicle digital communication system according to claim 2, wherein the reference signal generation circuit generates the reference signal based on an alternator noise component periodically generated inside the vehicle. Digital communication system.