JPH08102571A - Circuit board - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce high-frequency radiation noise from a digital circuit in a circuit board in which digital circuits and analog circuits coexist. An opto-electric converter 6 and 7 are provided in the vicinity of a CPU 1 of a digital circuit and a device connected to the CPU 1, and data of a data bus and an address bus, which change at high speed, are converted into optical signals to convert the opto-electric converter 6. , 7 are connected by an optical transmission line to perform data transfer. [Effect] It is possible to reduce the radiation noise from the wiring of the digital circuit in the circuit board and increase the packaging density of circuit components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital VTR or C in which analog circuits and digital circuits are mixed on the same substrate.
Regarding D and the like, the present invention relates to a circuit board that suppresses radiation noise that adversely affects the analog circuit and the outside of the board by a high-speed digital signal of the digital circuit.

[0002]

2. Description of the Related Art Recently, digital circuits such as a microcontroller are indispensable for electronic equipment, and a microcontroller is used as a control circuit inside the electronic equipment to provide high precision control and advanced man-machine interface. Has been realized.

On the other hand, environmental problems have been highlighted as an important issue, and it is necessary to suppress electromagnetic field radiation from electronic devices in consideration of the influence on other electronic devices and the human body.

A circuit configuration inside a conventional electronic device will be described with reference to the drawings. In FIG. 3, 1 is a CPU that suppresses all electronic devices, 2 is a ROM that stores a control program, 3 is a RAM that temporarily stores control data, and 4 is a CPU that outputs the data of the CPU 1 to an external circuit. Or send data from an external circuit to the CPU1,
Alternatively, an interface circuit (I / O circuit) for outputting a control signal to an internal analog signal processing circuit, 5 is an analog signal processing circuit which is an original function of an electronic device, and 6 is a CPU 1 and I / O 4, ROM 2, RAM 3 An address bus connecting the two, 7 is the CPU 1, I / O 4, and RAM
3, data bus connecting ROM2, 8 I / O 4 and I / O bus for communication with external circuits, 9 I / O
A control line 10 for controlling the analog signal processing circuit 5 via 4 is an input / output of the analog processing circuit 5. Address bus and data bus are 8 bits, 16
The data width increases to 32 bits and 32 bits, and the number of address buses tends to increase due to high-level control, and the area occupied by these data buses and address buses on the circuit board becomes large. In addition, the length of routing these buses becomes long. Moreover, since digital signals pass back and forth between the address bus and the data bus, these buses play the role of high-frequency antennas, and radiate noise to the outside of the circuits and the equipment in the vicinity to cause adverse effects.

[0005]

[Problems to be Solved by the Invention]
With the trend toward miniaturization, the processing speed of microcontrollers built into electronic devices will improve day by day,
At the same time, the clock frequency is very fast, from several Mz to several tens Mz, and the address bus and the data bus are fast and move at a speed of 1 / several times of the clock frequency.

On the other hand, with the miniaturization of equipment, electromagnetic separation between the digital circuit system and the analog circuit system is not sufficient, and the digital circuit system and the analog circuit system must be arranged in the vicinity where they influence each other. In addition, the miniaturization pattern of these circuit mounting boards due to the miniaturization increases the line impedance and functions as an antenna for emitting electromagnetic waves that disturb these digital signal lines.

Further, due to the improvement in the driving ability of the CPU and its peripheral circuits due to the increase in speed, clock electromagnetic interference from the digital circuit system tends to increase. There is a problem that not only the noise to the analog processing circuit system but also the electromagnetic interference noise is emitted to the outside of the electronic device. As a measure against electromagnetic radiation noise, it is general to reduce the components of the digital signal above the fundamental frequency by a filter or the like.

However, this method is effective when the clock is operating at several Mz or less, but when operating at a high speed of several tens Mz at the clock frequency, the frequency to be attenuated is several hundreds. Since it is equal to or higher than Mz, the noise regulation target band cannot be reduced.

When used in such a high frequency band of several tens of MHz, the semiconductor also has no margin for delay. Therefore, when a high frequency component is suppressed by passing a filter through a transmission line, signal delay occurs and malfunction occurs. The phenomenon that is said will occur. As described above, the conventional configuration has a problem that it is difficult to reduce noise radiation.

The present invention solves the above problems, and an object of the present invention is to provide a circuit board which suppresses radiation noise from a digital circuit and improves the circuit packaging density.

[0011]

In order to achieve the above object, the present invention comprises a circuit board in which analog circuits and digital circuits coexist, in which the address bus and data bus lines of the digital circuit are constructed by optical transmission paths. , Micro controller, ROM, RAM, I /
Data is transmitted and received to and from O through an optoelectric converter, and a signal operating at a low speed is transmitted through an electric transmission path.

[0012]

In the circuit board having the above-mentioned structure, the line functions as an electromagnetic wave noise transmitting antenna by changing a large number of transmission lines routed between the mixed microcontrollers and the peripheral ICs connected thereto from the electric transmission line to the optical transmission line. Can be removed, and components can be mounted on this optical transmission path, so that the mounting density can be improved.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit board configuration diagram in which a digital circuit group and an analog circuit group according to an embodiment of the present invention are mixed. As shown in the figure, the circuit board has a CPU 1 for controlling all electronic devices, and various control signals such as a data bus, an address bus, and a read / write signal are output from the CPU 1. A ROM 2 for storing a device control program, a RAM 3 for temporarily storing data, an I / O 4 for interfacing with control targets inside and outside the device,
The analog processing circuit 5, the photoelectric converters 6 and 7, the optical data bus converted by the photoelectric converters 6 and 7, and the optical address bus are provided.

An opto-electrical converter 6 is provided near the CPU 1, and the opto-electrical converter 6 converts an electric signal of a data bus and an address bus into an optical signal to perform reversible conversion between the electric signal and the optical signal. I have to.

On the other hand, an opto-electric converter 7 is provided near the ROM2, RAM3, and I / O4 devices, and the opto-electric converter 7 performs reversible conversion between an optical signal and an electric signal. , I am trying to connect to the address bus. The opto-electric converters 6 and 7 are connected by an optical data bus and an optical address bus of an optical transmission line to form a digital circuit system. Reference numeral 5 in the figure is an analog processing circuit.

Next, regarding the operation of the photoelectric converters 6 and 7,
An example of the data flow of the CPU 1 and the RAM 3 will be described with reference to FIG. The internal configuration of the photoelectric converters 6 and 7 is as follows. The photoelectric converter 6 connected to the CPU 1 includes an analog SW 6A, an analog SW 6B, (light emitting element 6C, 6F, a light receiving element 6D, an inverter 6E) (this analog SW is in an ON state at the "H" level).
The photoelectric converter 7 connected to a device other than the CPU 1 includes light receiving elements 7A and 7F, a light emitting element 7B, an analog SW 7C,
7D and inverter 7E.

When data is transferred from the CPU 1 to the RAM 3, the transfer data is output from the CPU 1 to the data bus and the RAM address is output to the address bus. The read / write signal is at the “L” level because it represents the state of writing data to the RAM. Analog SW is inverter 6E and 6A is O
N and 6B are OFF, and light is converted into optical data by the light emitting element 6C through the analog SW 6A and transmitted to the optical data bus.
The address data is transmitted to the optical address bus via the light emitting element 6F. The opto-electric converter 7 on the side of the RAM 3 reversely converts optical data from the optical data bus by the light receiving element 7A, and the analog SW 7C is turned on by the inverter 7E, and RA
It is transmitted to the data bus of M3.

The optical address data is inversely converted by the light receiving element 7F and transmitted to the RAM address bus. RAM3 to CP
When transferring data to U1, the CPU1 outputs the address data of the RAM3 to the address bus, and the light emitting element 6F,
It transmits to the address bus of RAM3 via the light receiving element 7F.

The RAM 3 stores data on the data bus.
In the case of data transfer from the RAM 3, the read / write signal becomes "H" level, the analog SW 7D is in the ON state, and the RAM data is transferred to the optical data bus by the light emitting element 7B. In the photoelectric converter 6 on the CPU 1 side, the optical data can be inversely converted by the light receiving element 6D, and the data can be transferred to the CPU 1 by being placed on the data bus through the analog SW 6B.

The opto-electric converters 6 and 7 are the CPU 1 and RO.
Each of M2, RAM3, data I / O4, etc. may be incorporated in the device chip. This photoelectric converter 6, 7
Is a circuit board in which light receiving and emitting portions are arranged at a predetermined interval and light can pass therethrough.

In order to connect the optical address terminals and the optical data signal terminals of the opto-electric converters 6 and 7 mounted on the circuit board, the optical transmission lines are buried so as to match the arrangement of the light emitting and receiving parts. By selecting a material having a high refractive index for this optical transmission line, the light entering the transmission line is repeatedly transmitted through the total reflection so that the light does not leak to the outside of the transmission line.

As a result, a sufficient crosstalk suppression rate can be obtained even if the distance between the light emitting and receiving portions of the opto-electric converters 6 and 7 is set to a narrow IC terminal pitch. By embedding the optical transmission line in the circuit board, an analog circuit can be mounted on the upper surface of the board. Moreover, since there is no electrical signal leakage or noise leakage from the optical transmission line, stable signal processing is possible.

[0023]

As is clear from the above description, according to the circuit board of the present invention, the I / O line and the address which can simultaneously satisfy the contradictory phenomena of high speed of the microcontroller and suppression of electromagnetic noise. By changing to a line optical transmission line, circuit components can be mounted on it, and the effect that the mounting density can be increased can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a circuit board according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a photoelectric converter on the circuit board.

FIG. 3 is a block diagram of a conventional circuit board.

[Explanation of symbols]

 1 CPU 2 ROM 3 RAM 4 I / O 5 analog processing circuit 6 photoelectric converter 7 photoelectric converter 6A analog SW 6B analog SW 6C light emitting element 6D light receiving element 6E inverter 6F light emitting element 7A light receiving element 7B light emitting element 7C analog SW 7D Analog SW 7E Inverter 7F Light receiving element

Claims (1)

[Claims] 1. An opto-electric converter having a mixed analog circuit group and digital circuit group, and comprising an address bus and a data bus of all digital circuit devices composed of a light emitting means and a light receiving means is provided. The circuit board characterized in that the address bus and the data bus of are formed by optical transmission lines, and the transmission lines of analog signals are formed by conductive patterns.