JP2013045856A - Printed circuit board and radiation noise suppression method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that although an input impedance (Z11) reduction method for suppressing power supply terminal noise or a transfer impedance (Z21) reduction method for suppressing noise propagation has been studied, the EMI countermeasure requires to suppress radiation noise of the whole system by cooperation design of the printed circuit board alone and the whole system (chip+package+board).SOLUTION: In a printed circuit board mounting an LSI, radiation noise is suppressed by controlling the transfer impedance (Z21) from the LSI terminal to the end of the printed circuit board, and evaluating the whole system including the LSI.

Description

Causes of radiation noise include (a) high-speed signal system common mode radiation, (b) radiation from packages and heat sinks, (c) radiation from slits, (d) power system resonance, (e) radiation from cables, etc. The present invention relates to (d) suppression of radiation noise generated from power supply system resonance, and in particular, printing in which the transfer impedance (Z21) of the entire power supply system including the semiconductor integrated circuit (LSI) is reduced. The present invention relates to a substrate and a method for suppressing radiation noise thereof.

  Conventionally, a countermeasure with a capacitor is generally used to suppress radiation noise generated from power system resonance, and a countermeasure with a single printed circuit board has been the mainstream, and transfer impedance (Z21) is used to reduce power system noise. It was rarely handled, and it was a countermeasure for cut-and-try based on measurement and suppression of voltage fluctuations due to the capacitor placement method.

Further, an increase in the amount of current accompanying the operation of the semiconductor causes an increase in power supply terminal noise. This power supply terminal noise propagates through the printed circuit board, causing unnecessary electromagnetic radiation (EMI).

In Patent Document 1, by optimizing the number of decoupling capacitors mounted in the vicinity of the power supply terminal of the LSI for each LSI, the high frequency power supply current is suppressed, the mounting space is reduced and the material cost is reduced. A printed circuit board design method that enables stable operation and EMI reduction has been proposed. This is because design information such as LSI output buffer type, which has been designed in the LSI design process, can be designed in the pattern design process. The completed design information is used.

JP 2002-73716 A

  Up to now, studies have been made on the input impedance (Z11) reduction method for the purpose of suppressing power supply terminal noise and the transfer impedance (Z21) reduction method for the purpose of suppressing noise propagation. Because the impedance characteristics of the printed circuit board alone and the entire system (chip + package + board) are different, the power supply noise of the entire system should be verified by co-designing the LSI and board instead of the printed circuit board alone. Therefore, it is necessary to implement EMI countermeasures.

  The present invention is a system including an LSI by controlling the transfer impedance (Z21) from the chip inside the LSI to the end of the printed circuit board even when the design information of the LSI and the pattern design process is not completed. The overall evaluation is performed to provide a printed circuit board in which radiation noise is suppressed.

  According to the first aspect of the present invention, the printed circuit board is controlled so that the anti-resonance (high impedance point) due to the capacitor on the printed circuit board and the parasitic components (inductance and capacitance) of the printed circuit board does not match the noise frequency of the semiconductor integrated circuit (LSI). A printed circuit board obtained by suppressing radiation noise.

  The invention of claim 2 is controlled so that the anti-resonance (high impedance point) does not coincide with the noise frequency by reducing the transfer impedance (Z21) from the semiconductor integrated circuit (LSI) serving as a noise source to the printed circuit board end. In the printed circuit board, the obtained printed circuit board has reduced radiation noise.

  According to a third aspect of the present invention, there is provided a printed circuit board in which the reduction of the transfer impedance (Z21) is designed in cooperation with an impedance model of a semiconductor integrated circuit (LSI) and an impedance model of the printed circuit board. The printed circuit board thus obtained has suppressed radiation noise.

  The invention of claim 4 is characterized in that the cooperation is due to a change of a capacitor, and by selecting a capacitor, a printed circuit board in which radiation noise is suppressed is obtained.

  According to a fifth aspect of the present invention, there is provided a printed circuit board for controlling an anti-resonance (high impedance point) due to a capacitor on the printed circuit board and parasitic components (inductance and capacitance) of the printed circuit board not to coincide with a noise frequency of a semiconductor integrated circuit (LSI). In the method for suppressing radiation noise, the obtained printed circuit board has radiation noise suppressed.

According to a sixth aspect of the present invention, the control reduces the transfer impedance (Z21) from the semiconductor integrated circuit (LSI) serving as a noise source to the printed circuit board end to reduce the anti-resonance (high impedance point) and the noise frequency. A method for suppressing radiation noise of a printed circuit board that does not match, wherein the obtained printed circuit board has radiation noise suppressed.

The invention according to claim 7 is a printed circuit board radiation noise suppression method for reducing the transfer impedance (Z21) by coordinating an impedance model of a semiconductor integrated circuit and an impedance model of the printed circuit board, and is obtained. The printed circuit board has reduced radiation noise.

The invention according to claim 8 is characterized in that the cooperation is based on a change of a capacitor, and by selecting the capacitor, radiation noise of the printed circuit board can be suppressed.

  According to the present invention, even when the design information is not completed, the radiation noise is reduced by controlling the transfer impedance (Z21) from the LSI to the printed circuit board end, and the LSI impedance model By coordinating with the impedance model of the printed circuit board, a printed circuit board with reduced radiation noise is obtained.

It is the schematic of the printed circuit board evaluation board of this invention. It is a simulation circuit for impedance model analysis of an LSI model board and a motherboard. It is a FFT result of the current waveform of the printed circuit board evaluation board when the LSI model board is mounted on the motherboard of the first embodiment. It is a measurement result which shows the relationship between Z21 of Example 1, and radiation noise. It is a measurement result which shows the relationship between Z21 of Example 2, and radiation noise. It is a measurement result which shows the relationship between Z21 of Example 3, and radiation noise. It is a measurement result which shows the relationship between Z21 of Example 4, and radiation noise. It is a measurement result which shows the relationship between Z21 of Example 5, and radiation noise. It is a measurement result which shows the relationship between Z21 of Example 6, and radiation noise. It is a measurement result which shows the relationship between Z21 of Example 7, and radiation noise. It is a measurement result which shows the relationship between Z21 of Example 8, and radiation noise.

Fabrication of LSI model board and mother board In order to obtain arbitrary power supply impedance characteristics, as shown in Fig. 1, capacitors are mounted on each board, and the combination of both boards is likely to generate noise. A difficult evaluation board was produced.

The LSI model board circuit configuration is a PRBS signal generation board made up of a crystal oscillator, Shift Register, EXOR, and Buffer / Driver, and the clock frequency is 48 MHz. In order to limit the evaluation object to Buffer / Driver noise, the power supply was separated from the other ICs, and the board was a 900 mm BGA of 32 mm × 32 mm size modeled on a general purpose BGA package.

Motherboard <br/> substrate center to the LSI model boards can be mounted, supplied with power from a stabilized power supply, and can be mounted a capacitor between LSI model board directly below and the entire substrate of the power supply ground.

Current profile acquisition The potential difference between both ends of the resistance for current measurement (0.05Ω) was measured, and the current waveform was calculated from I = V / R. Further, the current waveform was FFTed to obtain frequency data. A digital oscilloscope (Agilent Technologies DSA90804A) was used for the measurement.

Power supply impedance simulation In the simulation circuit as shown in FIG. 2, the impedance model of the LSI model board and the motherboard is extracted from the planar electromagnetic field analysis (Ansys SI Wave) using the S parameter, and the internal impedance of the noise source IC (Buffer / Driver) Was calculated from the Z11 measurement and modeled as the LCR lumped constant. In this embodiment, the power source terminal of the noise source IC is used as a temporary noise source and a port is provided.

The substrate end voltage was measured using a substrate end voltage measurement spectrum analyzer (ADVANTEST R3131A), and after confirming that the measurement results at the four ends of the substrate were almost the same, the measurement was made at one representative location.

Radiation noise measurement In order to measure the radiation noise suppression effect of the printed circuit board, a small anechoic chamber (external dimensions: 7 m x 3 m x 3 m, antenna-to-sample distance: 3 m, antenna height: 1 m (fixed) ) To measure the radiation noise. The evaluation board was placed at the center of the turntable, the stabilized power source was placed under the table, and measurement was performed with EMC MEASUREMENT SYSTEM (Toyo Technica).

From the FFT result of the current profile, as shown in FIG. 3, the current component up to the third harmonic (144 MHz) of the clock frequency (48 MHz) is significant, and the printed circuit board suppresses radiation noise at these frequencies. A 0.01 μF capacitor is required to suppress 48 MHz noise, a 2200 pF capacitor is required to suppress 96 MHz noise, and a 1000 pF capacitor is required to suppress 144 MHz noise. These were combined because of their effectiveness.

The capacitors mounted on the LSI model board and the motherboard were set as shown in Table 1, and the radiation noise was evaluated. The capacitor was selected so that the transfer impedance (Z21) was increased or decreased at the noise frequency.

  Table 2 shows Z21 and substrate end voltage for each noise frequency.

  There is a correlation between Z21 and the substrate end voltage. Under the condition that the clock frequency (48 MHz) and its harmonics (96 MHz, 144 MHz) have a high impedance, noise increases, and Z21 contributes to noise propagation.

From the far-field radiation noise measurement results, as shown in Table 3 and FIGS. 4 to 11, the increase / decrease tendency of Z21 coincides with the increase / decrease tendency of the radiation noise level.

In order to suppress radiation noise from the printed circuit board, it is effective to reduce the transfer impedance (Z21) from the LSI to the printed circuit board edge, and to coordinate the LSI impedance model with the printed circuit board impedance model. The obtained printed circuit board is a printed circuit board with reduced radiation noise.

1: printed circuit board, 2: motherboard, 3: LSI model board, 4: noise source, 5: large-capacitance capacitor, 6: choke coil, 7: external power supply, 8: ground, 9: power supply

Claims (8)

A printed circuit board characterized in that an antiresonance (high impedance point) due to a capacitor on the printed circuit board and parasitic components (inductance and capacitance) of the printed circuit board does not coincide with a noise frequency of a semiconductor integrated circuit. 2. The printed circuit board according to claim 1, wherein the control is performed by reducing a transfer impedance from a semiconductor integrated circuit serving as a noise source to the printed circuit board end. The printed circuit board according to claim 2, wherein the transfer impedance reduction is designed by coordinating an impedance model of a semiconductor integrated circuit and an impedance model of the printed circuit board. 4. The printed circuit board according to claim 3, wherein the cooperation is by changing a capacitor. A method for suppressing radiation noise, comprising controlling anti-resonance (high impedance point) due to a capacitor on a printed circuit board and parasitic components (inductance and capacitance) of the printed circuit board so as not to coincide with a noise frequency of a semiconductor integrated circuit. 6. The radiation noise suppression method according to claim 5, wherein the control is performed by reducing transfer impedance from a semiconductor integrated circuit serving as a noise source to a printed circuit board end. The radiation noise suppression method according to claim 6, wherein the transfer impedance is reduced by coordinating an impedance model of a semiconductor integrated circuit and an impedance model of the printed circuit board. The radiation noise suppression method according to claim 7, wherein the cooperation is by changing a capacitor.

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