KR20080022407A - Pcb with low emi noise - Google Patents

Abstract

A PCB(Printed Circuit Board) with low EMI(Electromagnetic Interference) noise is provided to reduce the EMI noise by dispersing an EMI noise peak in a frequency domain through the routing of a trace not to simultaneously switch n-bit data bus signals. A PCB includes a plurality of traces(111) between a driver(200) and a receiver(300). The driver outputs n-bit data bus signals switching at a predetermined clock rate. The receiver is inputted with the n-bit data bus signals outputted by the driver. The plurality of traces is transmitted with the n-bit data bus signals by being prepared to correspond to n-bit data respectively. Each of the plurality of traces includes first and second traces(111a,111b) and a series resistor(120). The first trace is connected to the driver and the second tracer is connected to the receiver. The series resistor is connected between the first and second traces for impedance matching.

Description

PCB with reduced EMI noise {PCB WITH LOW EMI NOISE}

1 is a circuit diagram showing the configuration of a PCB according to the prior art,

2 to 5 are circuit diagrams showing the configuration of a PCB according to the first to fourth embodiments of the present invention.

Explanation of symbols on the main parts of the drawings

101 ~ 104: PCB 111 ~ 114: Trace

111a to 114a: first trace 111b to 114b: second trace

200: driver 300: receiver

120: series resistance

The present invention relates to a PCB capable of reducing radiated EMI noise. More specifically, the present invention relates to a PCB capable of effectively reducing noise generated by simultaneous switching of n-bit data bus signals.

1 is a circuit diagram showing the configuration of a PCB 10 according to the prior art. Referring to FIG. 1, the driver 20 and the receiver 30 may be mounted on the PCB 10. The driver 20 and the receiver 30 may each be, for example, a memory controller and a memory implemented in the form of a chip. A trace 11 for transmitting a data bus signal is provided on the PCB 10 between the driver 20 and the receiver 30. Trace 11 is printed on PCB 10 as a conductive medium. The data bus signal generated by the driver 20 is switched at a predetermined clock rate and transmitted to the receiver 30. The data bus signal may be n-bit, and correspondingly, n drivers 20, receivers 30, and traces 11 are provided on the PCB 10. In addition, a series resistor 12 for impedance matching between the driver 20 and the receiver 30 may be provided in series with each trace 11. In this case, each trace 11 may be divided into a first trace 11a and a second trace 11b with the series resistor 12 in the center.

On the other hand, typically, when an IC device switches, a voltage fluctuation occurs while the current supplied from the power layer of the PCB changes momentarily and the current flowing to the ground layer changes rapidly. ), Which is called SSN (simultaneous switching noise). This SSN reduces the current supplied to the driver 20, which prevents the driver 20 from exhibiting perfect drive performance. Therefore, a system logic error such as a glitch may be generated to reduce the system performance. The reliability is low and EMI problems can occur.

According to the prior art, referring to FIG. 1, the total length of the trace 11 from the driver 20 to the receiver 30 (see "A" + "B") is the same, and the position of the series resistor 12 is equal. Is equally away from each driver 20 (see "A"). That is, according to the prior art, since the length of the trace 11 and the position of the series resistor 12 between each n-bit data bus are all equal, there is a problem that the SSN is increased. This is because a flow of voltage occurs while the driver 20 switches, because a large voltage flow occurs if not n devices switch at the same time.

The peak value of EMI noise due to this simultaneous switching is well observed in the frequency domain rather than in the time domain. The peaks of the EMI noise observed in these frequency domains are raised all at once in a particular frequency band, resulting in radiated EMI problems. In particular, in the present situation where the level of the voltage supplied to the IC device continues to decrease, high frequency noise such as SSN greatly affects the performance and stability of the system. In addition, since the operating frequency is increasing in recent years, a method of changing the switching speed of the IC device cannot be a measure for preventing EMI noise.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and to provide a PCB that can reduce the radiated EMI noise by dispersing the EMI noise peak in the frequency domain by routing the traces so that the n-bit data bus signal does not switch simultaneously. The purpose.

In order to achieve the above object, the present invention provides a driver for outputting an n-bit data bus signal (where n is an integer of 2 or more) for switching at a predetermined clock rate, and the n-bit data output by the driver. In a PCB having a plurality of traces for receiving the n-bit data bus signal is provided between the receiver receiving the bus signal, each of the plurality of traces are connected to the driver A first trace; A second trace coupled to the receiver; And a series resistor for impedance matching connected between the first trace and the second trace, wherein lengths of at least two of the plurality of first traces and / or the plurality of second traces are uneven. Provides a PCB.

The length between the first trace and / or the second trace may be cyclically equal in pairs (m is an integer of 2 or more less than n).

In the plurality of traces, the sum of the first trace and the corresponding second trace may be equal.

First, a principle for eliminating EMI noise caused by simultaneous switching of n-bit data bus signals will be described. Typically, the absolute size (Vnoise) of the SSN is the same as [Equation 1].

[Equation 1]

Vnoise = L * (dI / dt) (L: inductance, I: amount of current supplied, t: time during which the current is rapidly changing)

As can be seen from Equation 1, the greater the inductance of the SSN, the greater the amount of current supplied to the IC element, and the shorter the switching time of the IC element, the greater the noise generation amount. If L, I, and t are all fixed variables, the method for reducing SSN is to make the switching time between the respective IC devices different. That is, if the switching time of the n-bit data bus line is alternately switched with a certain time difference, the high frequency noise can be removed by reducing the SSN, thereby reducing the amount of radiated EMI. This method does not cause a problem in the operating performance of the system.

Specifically, in this embodiment, the traces are routed at a distance from the passive elements to prevent the n-bit data bus signals from switching at the same time and reduce the amount of radiated EMI of the SSN.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 2 to 5 are circuit diagrams showing the configuration of the PCBs 101 to 104 according to the first to fourth embodiments of the present invention. The driver 200 and the receiver 300 may be mounted on the PCBs 101 to 104. The driver 200 and the receiver 300 may each be, for example, a memory controller and a memory implemented in the form of a chip. Between the driver 200 and the receiver 300, traces 111 to 114 for transmitting data bus signals are provided on the PCBs 101 to 104. Traces 111-114 are printed on PCBs 101-104 as conductive media. The data bus signal generated by the driver 200 is switched to a predetermined clock rate and transmitted to the receiver 300. The data bus signal may be n-bit, and correspondingly, n drivers 200, receivers 300, and traces 111 to 114 are provided on the PCBs 101 to 104. In addition, a series resistor 120 for impedance matching may be provided in series between the traces 111 to 114 between the driver 200 and the receiver 300. In this case, each of the traces 111 to 114 may be divided into first traces 111a to 114a and second traces 111b to 114b with the series resistor 120 at the center thereof.

First, referring to FIG. 2, in the PCB 101 according to the first embodiment of the present invention, the total length of the traces 111 between the drivers 300 in the driver 200 is equal to “A” + “B”. However, the first trace 111a is routed in two pairs so that the distance from the driver 200 to the series resistor 120 is cyclically equal. That is, 1st, 3rd, 5th ... first traces 111a between each other (see "A") and 2nd, 4th, 6th ... 1st traces 111a between each other ("A-ΔL"). Lengths are equal, and the lengths (see "A" and "A-ΔL") between adjacent first traces 111a of the first and second, third and fourth ... adjacent to each other are uneven. In this case, the difference in length of the first trace 111a is compensated by the length of the second trace 111b (see "B" and "B + ΔL"). According to the present embodiment, the SSN can be reduced because the devices switch at 1/2 rather than at the same time.

Next, referring to FIG. 3, in the PCB 102 according to the second embodiment of the present invention, the total length of the traces 112 between the receivers 300 in the driver 200 is equal to "A" + "B". . However, the first trace 112a is routed unevenly from the driver 200 to the series resistor 120 ("A", "A-ΔL1", ..., "A-ΔL (n-)). 2) "and" A-ΔL (n-1) ". The difference in length of the first trace 112a is compensated by the length of the second trace 112b ("B", "B + ΔL1", ..., "B + ΔL (n-2)" and See "B + ΔL (n-1)"). In this case, since the n IC devices switch at different times, the SSN removal effect is improved compared with the first embodiment.

Next, referring to FIG. 4, in the PCB 103 according to the third embodiment of the present invention, the overall length of the trace 113 between the receivers 300 in the driver 200 is different. In particular, as in the first embodiment, the first trace 113a is routed in two pairs so that the distance from the driver 200 to the series resistor 120 is cyclically equal ("A" and "A-"). ΔL "). However, the lengths of the second traces 113b are all equal to " B ", and the lengths of the different first traces 113a are not compensated for.

Next, referring to FIG. 5, in the PCB 104 according to the fourth embodiment of the present invention, the total length of the traces 114 between the receivers 300 in the driver 200 is different. In particular, as in the second embodiment, the first trace 114a is routed unevenly from the driver 200 to the series resistor 120 ("A", "A-ΔL1", ..., See "A-ΔL (n-2)" and "A-ΔL (n-1)"). However, similarly to the third embodiment, the lengths of the second traces 114b are all equal to "B", and the lengths of the differenceed first traces 114a are not compensated for.

In the above, according to the present invention, a routing method of a PCB trace for reducing EMI has been described. In the routing according to the present invention, even though the length of the trace from the driver to the receiver of each of the n-bit data bus signals is equally routed, the position of the series resistor is cyclically positioned or all differently, so that the overall The switching time of the IC element can be made different. As a result, the SSN can be reduced to disperse the energy peak value rising in a specific band of the frequency domain, thereby reducing the amount of radiated EMI.

As mentioned above, the present invention has been described in detail through preferred embodiments, but the present invention is not limited thereto and may be variously implemented within the scope of the claims.

As described above, according to the present invention, by routing the traces so that the n-bit data bus signals do not switch simultaneously, radiated EMI noise can be reduced by dispersing EMI noise peaks in the frequency domain.

Claims (3)

N-bit between a driver for outputting an n-bit data bus signal (where n is an integer of 2 or more) switching at a predetermined clock rate and a receiver for receiving the n-bit data bus signal output by the driver In the PCB having a plurality of traces provided to correspond to each data and the n-bit data bus signal is transmitted, Each of the plurality of traces, A first trace coupled to the driver; A second trace coupled to the receiver; And a series resistor for impedance matching connected between the first trace and the second trace, The PCB of claim 1, wherein the lengths of at least two of the plurality of first traces and / or the plurality of second traces are uneven. The method of claim 1, The length of the first trace and / or the second trace is mutually equal to each other m m (but m is an integer of 2 or more less than n) in a pair cyclically equivalent. The method according to claim 1 or 2, Wherein the sum of the first trace and the corresponding second trace in the plurality of traces are all equal.

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