Description

SPREAD SPECTRUM CLOCK MODULATOR

[ 1 ] Field of the Invention

[2] The present invention relates to an electronic device comprising a controller which controls circuits that apply spread spectrum to the signals for reducing electromagnetic interference (EMI).

[3] Prior Art

[4] Undesirable impacts result due to the effect of the signals emitted by electronic devices or various circuits, and as a result of this, operation of devices, which are in the same environment and are subjected to these signals, are negatively impacted. This event is known as electromagnetic interference. Various methods are developed in order to reduce the electromagnetic interference observed in devices. One of these methods is to apply a process called spread spectrum to the signals in the devices. In this process, in order to reduce the possibility of the signals producing electromagnetic interference by concentrating in certain frequencies, the frequency of the signal (for example the signal of the clock oscillator) at which the electronic device is operated is not kept fixed, but it is periodically changed in a small range (2.5% - 5%). This way, it is ensured that signals are spread to different frequencies and they are prevented from concentrating in certain frequencies whereby electromagnetic interference is reduced.

[5] The United States patent document No. US2003118080, an application in the state of the art, discloses a method for reducing electromagnetic interference. According to the method, spread spectrum is applied to the master clock signal and a plurality of slave clock signals are obtained from this signal. Phases of the slave clock signals that will be used in driving different circuits within the system are changed. Electromagnetic interference is reduced by applying slave clock signals, having the same frequency value but different phases, to the circuits.

[6] The International patent application No. WO03039045, an application in the state of the art, discloses a solution aiming to reduce electromagnetic interference in the case that multiple clock frequencies overlap. A phase difference is introduced between the clock signals by applying different amounts of delays to them and thus overlapping of the signals is prevented.

[7] In the state of the art applications, the process of changing the clock frequency

(spread spectrum) in certain intervals is performed periodically. Hence, there is a frequency of this change as well and this frequency is called modulation frequency. In the current applications, electromagnetic interference is reduced by performing spread spectrum through making changes in the phase of the modulation frequency. However all the circuits that are driven with different signals use a single modulation frequency.

In the said applications, due to the reason that modulation frequency is not intervened, the reduction in the amount of electromagnetic interference remains limited and a more effective solution can not be provided.

[8] Summary of the Invention

[9] The objective of the present invention is to realize an electronic device comprising a controller that enables the peak value of the electromagnetic energy, which is emitted by the device or circuits to which it is connected to during operation thereof, to be lower.

[10] Another objective of the invention is to realize an electronic device comprising a controller that reduces the electromagnetic interference to which the other devices in the same environment or the circuits therein are exposed.

[11] A further objective of the invention is to realize an electronic device wherein a plurality of spread spectrum circuits located therein is controlled by a single controller.

[12] The electronic device, which is realized to fulfill the objective of the present invention and defined in Claim 1 and in its dependent claims, comprises a controller which generates separate control signals for each of the oscillators located at the input of a plurality of spread spectrum circuits. Thus, spread spectrum control of all circuits is performed by a single controller. Since the control signals sent to the spread spectrum circuits are signals different from each other which are obtained by changing the amplitude and/or frequency of the spread spectrum signal, the electromagnetic interference and associated undesirable results observed in devices or circuits are minimized.

[13] Detailed Description of the Invention

[14] The electronic device realized to fulfill the objective of the present invention is illustrated in the accompanying figures in which,

[15] Figure 1 is the schematic view of the inventive electronic device.

[16] Figure 2 is the frequency-time graphics of spread spectrum control signals having the same frequency but different phases (prior art).

[17] Figure 3 is the frequency-time graphics of spread spectrum control signals having the same amplitude but different frequencies.

[18] Figure 4 is the frequency-time graphics of spread spectrum control signals having different amplitudes, frequencies and phases.

[19] The components shown in the figures are numbered as follows:

[20] 1. Device

[21] 2. Circuit

[22] 3. Oscillator

[23] 4. Controller

[24] The inventive electronic device (1) comprises at least two circuits (2) where spread

spectrum is applied, an oscillator (3) at the input of each circuit (2) which provides the signal that drives the circuit (2), and a controller (4) which controls the signals being input to the oscillators (3) so as to reduce the electromagnetic interference (Figure 1).

[25] Spread spectrum is applied to the circuits (2) that carry out various functions in the device (1), so that the signals they emit do not negatively impact the other circuits and operation of the other devices in the environment. The signals sent to the circuits (2) in order to reduce the electromagnetic interference are set such that they overlap as little as possible.

[26] In order for the signals being input to the circuits (2) to be set; frequency, amplitude and/or phase values of the control signals (Sl, S2) transmitted by the controller (4) to the oscillators (3) are changed within desired ranges and a different control signal (Sl, S2) is sent to each oscillator (3). As required by the spread spectrum application, the control frequencies (Sl, S2) of the signals transmitted to the oscillators (3) are increased or decreased around the frequency value (central frequency) (e.g. ± 5%) to be transmitted to the circuits (2). The frequency of the frequency change in the said range is called the modulation frequency.

[27] The controller (4) produces different control signals (Sl, S2) for each oscillator (3) by making changes in the modulation frequency, amplitude and/or phase of the master clock signal. The control signals (Sl, S2) are obtained by changing the frequency, amplitude and/or phase values of the master clock signal within the maximum and minimum values range determined during production or use. Since it is aimed to prevent concentration of electromagnetic energy in certain frequencies, the control signals (Sl, S2) transmitted to the oscillators (3) should be set such that they will overlap in a plurality of different frequencies. When the controller (4) is generating different control signals (Sl, S2), it makes changes not only in the phase but also in the amplitude and modulation frequency of the master clock signal. This way, concentration of the overlapping between the control signals (Sl, S2) in a limited number of frequencies is prevented and the number of overlapping frequencies is increased. Thus, a more effective spread spectrum is applied in the device (1) and the problem of electromagnetic interference is minimized.

[28] In the prior art applications mentioned above, control signals are obtained by only applying the master signal in different phases without changing the frequency of the frequency change (modulation frequency). Yet in the inventive electronic device (1), while obtaining different control signals (Sl, S2) from the master signal, modulation frequency and/or amplitude values of the master signal are also changed by the controller (4) between the upper and lower limits. The number of frequencies where the control signals (Sl, S2), which are obtained by also changing the frequency and/or amplitude values, overlap with each other, increases. Thus, concentration of electro-

magnetic energy is distributed to more frequencies and negative electromagnetic impacts (interference) are reduced. Increase of the number of frequencies where the control signals (Sl, S2), which are obtained by changing the modulation frequency, phase and/or amplitude of the master signal, overlap is illustrated below by means of three examples:

[29] For a situation where the frequency change is in the form of a triangle wave and where two control signals are used,

[30] - In the case that control signals (Sl, S2) are different from each other only by phase difference, a situation like the one in Figure 2 occurs. Accordingly, two control signals overlap in two frequencies (fl, f2) and the electromagnetic energy density is concentrated at these two frequencies.

[31] - In the case that the modulation frequencies of the control signals (Sl, S2) are changed, the control signals (Sl, S2) overlap in three frequencies (fl, f2, f3) (Figure 3). In this case, since the number of frequencies where the control signals (Sl, S2) overlap increases, compared to the previous example, to three, electromagnetic energy density is distributed to three frequencies instead of two.

[32] - In the case that the amplitude and phases of the control signals (Sl, S2) are also changed in addition to their modulation frequencies, the control signals (Sl, S2) overlap at six frequencies (fl, f2, f3, f4, f5, f6) (Figure 3). In this case, since the number of frequencies where the control signals (Sl, S2) overlap increases, compared to the previous two examples, to six, electromagnetic energy density is distributed to six frequencies instead of two or three.

[33] In the second and third examples showing two applications of the spread spectrum process performed in the inventive electronic device (1), since electromagnetic energy density is distributed to more frequencies, a more effective spread spectrum is realized and the problem of electromagnetic interference is reduced.

[34] As it is seen from the above given examples, the controller (4) obtains different control signals (Sl, S2) by making changes in the modulation frequency, amplitude and/or phase of the master signal, and it uses these signals in driving the oscillators (3) located at the input of the circuits (2) within the device (1). This way, all the circuits (2) to which spread spectrum is applied in the electronic device (1) are controlled by means of a single controller (4) and a more effective spread spectrum result is attained.