JP2009118149A - Portable communication terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the higher harmonics of a clock signal driving an electronic part such as a memory, a camera, a display or the like interfere in the input side of a direct conversion mixer and reception characteristics are deteriorated. <P>SOLUTION: The portable communication terminal includes a receiving section 3 containing the direct conversion mixer mixing a partial-oscillator signal set to a frequency coinciding with the center frequency of a reception channel with the desired signal of a high frequency received by an antenna 1 and a DC-component removing means removing a DC component comprised in an output signal from the direct conversion mixer. The portable communication terminal further includes the electronic parts 10, 11 and 12 driven by the clock signal in a desired frequency. The frequency of the clock signal supplied to the electronic parts is set in one in which the higher harmonics of the clock signal interfere in the center frequency of the reception channel. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a portable communication terminal that suppresses noise caused by a clock for driving electronic components such as a camera, a display, and a memory.

  In recent years, mobile communication terminals such as mobile phones have been able to transmit and receive large amounts of data, and the amount of data that can be handled is large by providing a camera or display with a large number of pixels, a large capacity memory, etc. It has become. In order to read and write a large amount of data in the memory, it is necessary to increase the speed of the clock for driving the memory. However, increasing the clock speed increases noise.

  FIG. 7 is a block diagram showing a configuration of a general mobile phone. In FIG. 7, the signal line 11a of the display unit 11 and the signal line 10a of the camera 10 are often routed inside the mobile phone using a flexible cable or the like. Since the flexible cable easily radiates noise, when the noise of the signal passing through the flexible cable is large, a phenomenon occurs in which high-frequency noise radiated therefrom interferes with the antenna. As described above, when high-frequency noise interferes with the reception band of the mobile phone, the reception performance of the mobile phone deteriorates. Therefore, it is necessary to take measures to reduce the deterioration of the reception performance.

  In FIG. 7, for example, a magnetic sheet 21 for suppressing high-frequency noise is applied to the signal line of the display unit, and a filter 22 for suppressing high-frequency noise is applied to the signal line. The point which reduces deterioration of performance is disclosed by patent document 1. FIG.

JP 2005-184195 A

  In addition, the direct conversion type receiver has a problem that a signal from a local oscillator interferes with a mixer input unit and a DC offset is generated due to self-mixing. In order to solve this problem, Patent Document 2 discloses that a DC offset is canceled using a DC cut capacitor.

JP-A-11-225179

  By the way, in order to suppress the noise radiated from the flexible cable, if a shield countermeasure member is used, a space for mounting the shield countermeasure member and a fixed mounting area on the substrate are required. This is not preferable for reducing the thickness.

  A mobile communication terminal according to the present invention includes a direct conversion mixer that mixes a local oscillator signal set to a frequency that matches a center frequency of a reception channel of the desired signal with a high-frequency desired signal received by an antenna, and the direct conversion mixer. Including a DC component removing means for removing a DC component contained in the output signal from the receiver, converting the desired signal into a baseband signal, and an electronic component driven by a clock signal having a desired frequency. The frequency of the supplied clock signal is set to a frequency at which the harmonics of the clock signal interfere with the center frequency of the receiving channel.

  A mobile communication terminal according to the present invention includes a direct conversion mixer that mixes a local oscillator signal set to a frequency that matches a center frequency of a reception channel of the desired signal with a high-frequency desired signal received by an antenna, and the direct conversion mixer. Including a DC component removing means for removing a DC component contained in the output signal from the receiver, converting the desired signal into a baseband signal, and an electronic component driven by a clock signal having a desired frequency. The frequency of the supplied clock signal is set to a frequency at which the harmonics of the clock signal interfere with the center frequency of the receiving channel, so the harmonics of the clock signal for driving electronic components such as memory are directly used as high-frequency noise. Receivability when interfering with the input signal of the conversion mixer It is possible to reduce the deterioration of. In other words, a magnetic sheet for suppressing high frequency noise and a shield member such as a filter, which were conventionally required for the signal lines of the display unit, are no longer necessary, and the mobile phone can be reduced in size, thickness, and cost. .

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a mobile communication terminal according to the present invention. In FIG. 1, the received signal received by the antenna 1 is input to the receiving unit 3 and the signal processing unit 5 through the antenna duplexer 2. The receiving unit 3 and the signal processing unit 5 perform processing such as demodulation, voice decoding, conversion from a digital signal to an analog signal, and gain adjustment of the received voice, and output to the receiver 7 that is the receiving unit. The receiver 3 is provided with a direct conversion mixer. Conversely, the user's voice (speaker voice) input from the microphone 6 is processed by the signal processing unit 5 and the transmission unit 4 such as conversion from an analog signal to a digital signal, voice coding, modulation processing, and power amplification. Is transmitted to the outside via the antenna 1. The control unit 9 controls the functions of the mobile phone in general according to the transmission / reception function of the mobile phone, the processing by the application software stored in the memory 20, and the user's instruction input from the operation unit 8. In addition, a display unit 11 such as a camera 10 or a liquid crystal display is provided. Further, the control unit 9, the display unit 11, the camera 10, the operation unit 8, the reference oscillator 13 a that supplies a clock for driving the memory 20, the direct conversion mixer of the reception unit 3, and the reference oscillator that supplies the clock to the transmission unit 4. 13b is provided.

  FIG. 2 is a block diagram showing a configuration of the direct conversion mixer type receiving unit 3. The direct conversion receiver shown as an example in FIG. 2 includes a DC cut capacitor 11 in order to cancel a DC offset generated when a local oscillator signal from a local oscillator interferes with a mixer input unit. The operation will be described below. The high-frequency desired signal input to the receiving unit 3 in FIG. 1 is mixed with the local oscillator signal input from the local oscillator 18 by the direct conversion mixer 12 and converted into a baseband signal. The local oscillator 18 is generally a PLL (Phase Lock Loop) synthesizer, and generates a local oscillator signal to be output to the direct conversion mixer 12 based on the signal of the reference oscillator 13b. Since the desired signal output from the direct conversion mixer 12 is very weak, after the unnecessary frequency components other than the desired frequency band are removed by the filter 14, the operation of the A / D converter 17 at the subsequent stage is performed by the amplifier 15. Amplified to the extent that the tolerance is not exceeded. The DC cut capacitor 16 having a DC offset cancel function removes the DC offset component, and is then converted into a digital signal by the A / D converter 17 and output to the signal processing unit 5. The frequency of the local oscillator signal supplied by the local oscillator 18 is set so as to coincide with the center frequency of the reception channel including the desired signal.

  Here, the DC offset canceling function by the DC cut capacitor 16 will be described. FIG. 3 is an explanatory diagram for explaining processing for canceling a DC offset by a DC cut capacitor. 3A is an input signal of the direct conversion mixer 12, FIG. 3B is an output signal of the direct conversion mixer 12, and FIG. 3C is output from the DC cut capacitor 16, and is output to the A / D converter 17. Indicates the input signal. The thin dotted line indicates the center frequency of the reception channel (desired signal), the thick line indicates the interference signal from the local oscillator 18, the thick dotted line indicates the suppressed interference signal, and the shaded portion indicates the desired signal.

  In general, in the direct conversion mixer 12, since the local oscillator signal generated by the local oscillator 18 circulates to the input part of the direct conversion mixer 12, the signal input to the direct conversion mixer 12 includes a desired signal, Interference signals from the local oscillator 18 are included. In FIG. 3A, the desired signal included in the input signal to the direct conversion mixer 12 includes an interference signal from the local oscillator 18 having a frequency component equal to the center frequency of the reception channel (desired signal). It is shown.

  In the direct conversion mixer 12, the frequency of the local oscillator 18 is equal to the center frequency of the desired signal. Therefore, an interference signal to the mixer input section is mixed at the same frequency in the direct conversion mixer 12, and thus a DC (direct current) component. Is output as FIG. 3B shows that a desired signal converted into a baseband signal includes a self-mixed interference signal as a DC component. In general, the mixing operation for the interference signal from the local oscillator is referred to as self-mixing. Such an unnecessary DC component becomes a noise component included in the desired signal, which causes deterioration in reception performance. The direct conversion receiver is preferably equipped with a DC offset canceling function for eliminating this unnecessary DC component. When, for example, a DC cut capacitor 16 is used as a DC offset cancel function, as shown in FIG. 3C, the DC component that is a self-mixed interference signal is suppressed by the DC offset cancel function. .

  As described above, it is possible to reduce reception performance deterioration due to interference of the local oscillator signal from the local oscillator 18 on the input side to the direct conversion mixer 12. However, if the harmonics of the clock signal for driving a memory, camera, or liquid crystal display interfere with the antenna or receiver as high frequency noise, the frequency is different from that of the local oscillator signal. Depending on the cancellation process, it is not possible to reduce the degradation of reception performance. FIG. 4 is an explanatory diagram for explaining processing when a signal having a frequency other than the local oscillator signal interferes with the mixer input side as noise. 4A shows a signal input to the direct conversion mixer, and FIG. 4B shows a signal input to the A / D converter. In FIG. 4, the dotted line indicates the center frequency of the reception channel (desired signal), the thick line indicates noise, and the shaded portion indicates the desired signal.

  A frequency different from the local oscillator signal from the local oscillator 18, that is, a signal having a frequency different from the center frequency of the reception channel (= the frequency of the local oscillator signal) interferes at the input side of the direct conversion mixer 12, and FIG. When the desired signal is mixed together as described above, the interference signal is included in the desired signal as a high frequency noise component. The desired signal containing the high frequency noise component is converted into a baseband signal by the direct conversion mixer 12 and output to the A / D converter 17 via the amplifier 15. When the high frequency noise component is different from the center frequency of the desired signal, that is, the frequency of the local oscillator signal, the high frequency noise component does not become a DC component when converted to a baseband signal by the direct conversion mixer 12. That is, as shown in FIG. 4B, the noise component converted into the baseband signal is output as it is without becoming a DC component and cannot be removed by the DC cut capacitor 16. For this reason, the reception performance deteriorates due to the influence of noise superimposed on the desired signal.

  Therefore, the mobile communication terminal according to the present invention uses the frequency of the reference signal (clock signal) for operating the display unit 11, the camera 10, the operation unit 8, and the memory 20 as, for example, GSM (Global System for Mobile communications). Such a setting is made so that the harmonics of the reference signal (clock) interfere with the center frequency of the reception channel of the wireless communication system to be used. That is, the reference oscillator 13a selects the frequency of the reference signal (clock) supplied to the display unit 11, the camera 10, the operation unit 8, and the memory 20 so that the harmonics of the clock interfere with the center frequency of the reception channel.

  In the GSM system, the channel interval is 0.2 MHz in the frequency band of approximately 35 MHz from 925.2 MHz to 959.8 MHz, and the center frequency of the reception channel is used in increments of 0.2 MHz. Here, when the frequency of a clock used in the control unit 9 or a functional block connected to the control unit 9 (for example, the display unit 11, the camera 10, the operation unit 8, and the memory 20) is 12.0 MHz, 78 of 12.0 MHz. High-frequency noise of 936.0 MHz, which is the second harmonic, interferes with the GSM reception band. Since 936.0 MHz, which is the 78th harmonic of the clock signal having a frequency of 12.0 MHz, becomes the center frequency of the reception channel of the GSM system, the harmonics of the clock signal mixed as high frequency noise in the input signal to the direct conversion mixer 12. The wave is mixed by the direct conversion mixer 12 and converted into a DC component. Therefore, the noise is suppressed by the DC offset cancellation function of the direct conversion receiver.

  FIG. 5 is an explanatory diagram for explaining processing for removing noise when a signal other than the local oscillator signal interferes with the mixer input side as noise. FIG. 5A shows a signal input to the direct conversion mixer, and FIG. 5B shows a signal input to the A / D converter. In FIG. 5, the thin dotted line indicates the center frequency of the reception channel (desired signal), the thick line indicates noise, the thick dotted line indicates suppressed noise, and the shaded portion indicates the desired signal. Here, consider a case where the high frequency noise is the same as the center frequency (local oscillator frequency) of the reception channel. As shown in FIG. 5A, when the high frequency noise component has the same frequency as the local oscillator signal, the noise component converted into the baseband signal by the direct conversion mixer 12 becomes a DC component. Therefore, the noise component is suppressed by the DC offset canceling function (FIG. 5B). For this reason, in this case, it is possible to reduce deterioration in reception performance due to noise.

  In the GSM system, the channel interval is 0.2 MHz, and the center frequency of the reception channel is set as an integer multiple of 0.2 MHz. Therefore, the harmonic (integer multiple) of a specific frequency is always the center frequency of the reception channel. In order to achieve this, the specific frequency may be n × 0.2 MHz (n: integer). In the GSM system, for example, it has a reception band of about 92 MHz from 925.2 MHz to 959.8 MHz, and it is conceivable to select a clock of 35 MHz or more so as to avoid harmonic interference in the reception band. The selection of the clock frequency based on the present proposal is effective when a clock frequency that avoids interference of harmonics in the reception band due to block restrictions or the like cannot be selected. It should be noted that all functional blocks connected to the control unit, for example, the display unit 11, the camera 10, the operation unit 8, and the memory 20, may use a specific clock frequency, or only some functional blocks. May be used. In this case, in each functional block, the clock signal supplied from the reference oscillator 13a may be multiplied or divided to change to a desired clock frequency.

  As described above, when the harmonics of the clock signal for driving the electronic components such as the memory 20 interfere with the input signal of the direct conversion mixer 12 as high frequency noise, it is possible to reduce the deterioration of the reception performance. In other words, a magnetic sheet for suppressing high frequency noise and a shield member such as a filter, which were conventionally required for the signal lines of the display unit, are no longer necessary, and the mobile phone can be reduced in size, thickness, and cost. .

Embodiment 2. FIG.
FIG. 6 is a block diagram showing a configuration of the mobile communication terminal according to Embodiment 2 of the present invention. In FIG. 6, the same reference numerals as those in FIG. As shown in FIG. 1, the mobile communication terminal according to Embodiment 1 includes a reference oscillator 13a that supplies a clock signal for driving electronic components such as a camera 10, a display unit 11, and a memory 20, and a direct conversion mixer 12. And a reference oscillator 13b for supplying a reference signal to the transmitter 3 and the transmitter 4. On the other hand, the portable communication terminal according to the second embodiment shares a reference oscillator that supplies a reference signal to the receiving unit 3 and a reference oscillator that supplies a clock signal to an electronic component. A clock signal is generated using a reference signal. This is particularly effective when the frequency of the clock signal supplied to the electronic component can be the same as the reference signal supplied to the receiving unit.

  Since it is not necessary to provide a reference oscillator for supplying a clock signal for driving an electronic component such as a memory, this further contributes to miniaturization and cost reduction of the mobile phone. Further, since the reference oscillator used in the receiving unit 3 has the same frequency as that of the radio system, the frequency of the harmonics of the clock used in the control unit 19 is matched with the center frequency of the receiving channel of the system with high accuracy. be able to. As a result, the noise component output from the direct conversion mixer 12 becomes a DC frequency component close to ideal, and the effect of the DC offset canceling function can be utilized to the maximum extent.

Embodiment 3 FIG.
The portable communication terminal according to the second embodiment shares a reference oscillator that supplies a reference signal to the receiving unit 3 and a reference oscillator that supplies a clock signal to an electronic component. The reference signal from the reference oscillator 13b shown in FIG. The clock signal is generated using Thus, by sharing the reference oscillator that supplies the reference signal to the receiving unit 3 and the reference oscillator that supplies the clock signal to the electronic component, the reference oscillator can be used to supply the clock signal for driving the electronic component such as a memory. There is no need to provide this, which has the effect of reducing the size and price of the mobile phone. Further, since the reference oscillator used in the receiving unit 3 has the same frequency as that of the radio system, the frequency of the harmonics of the clock used in the control unit 19 is matched with the center frequency of the receiving channel of the system with high accuracy. There was also an effect of being able to.

  Hereinafter, the portable communication terminal according to the third embodiment of the present invention to be described provides a reference oscillator that supplies a reference signal to the receiving unit 3 and a clock signal to the electronic components, similarly to the portable communication terminal according to the second embodiment. 6 is provided with means for setting the frequency of a clock signal for driving an electronic component such as a memory to an arbitrary frequency, and the control unit 19 sets the frequency to an arbitrary frequency. The configured clock signal is configured to be supplied to the electronic component.

  Specifically, in order to operate the control unit 19 or a functional block connected to the control unit 19 (for example, the display unit 11, the camera 10, the operation unit 8, and the memory 20) at a specific clock frequency, the control unit 19 receives There is provided means for newly generating a clock on the basis of a reference signal supplied to the unit 3, that is, a signal output from the reference oscillator 13. As a result, it is possible to generate and use an arbitrary frequency within the control unit 19. An example of a means for generating a new clock is a PLL synthesizer. Further, the multiplier circuit and the frequency divider circuit are examples of means for generating a new clock. Note that the functional block connected to the control unit 19, for example, all the functional blocks such as the display unit 11, the camera 10, the operation unit 8, and the memory 20 may use a clock newly generated in the control unit 19. Only some of the functional blocks may be used. Moreover, a specific clock frequency with all the functional blocks may be used, or only some of the functional blocks may be used. A specific clock frequency is not limited to a specific one. It may be selected so that the harmonics of the clock interfere with the center frequency of the receiving channel of the wireless communication system to be used. A plurality of specific clock frequencies may be set for each functional block or for each of a plurality of functional blocks.

  As described above, the reference oscillator that supplies the reference signal to the receiving unit 3 and the reference oscillator that supplies the clock signal to the electronic component are shared, and the control unit 19 drives the electronic component such as a memory. By providing means for setting the frequency of the signal to an arbitrary frequency, there is no need to provide a reference oscillator for supplying a clock signal for driving an electronic component such as a memory, which contributes to miniaturization and cost reduction of the mobile phone. The same effect as in the first and second embodiments can be obtained, in which the harmonic frequency of the clock used in the control unit 19 can be matched with the center frequency of the reception channel of the system with high accuracy. Further, the clock frequency of the control unit 19 or a functional block connected to the control unit 19 (for example, the display unit 11, the camera 10, the operation unit 8, and the memory 20) is arbitrarily set without being restricted by the clock frequency of the receiving unit 3. Therefore, it is possible to set a high clock frequency in accordance with the application and specifications of the electronic component, and it is possible to cope with the high functionality of the control unit.

  For example, when the frequency of the clock used in the control unit 19 or a functional block connected to the control unit 19 (for example, the display unit 11, the camera 10, the operation unit 8, and the memory 20) is set to a relatively high frequency of 30.0 MHz. Furthermore, taking the GSM system described in the first embodiment as an example, high frequency noise of 930.0 MHz, which is the 31st harmonic of the frequency 30.0 MHz of the clock used in the control unit 19, interferes with the GSM reception band. . However, since 930.0 MHz is the center frequency of the reception channel of the GSM system, noise is suppressed at the time of input to the A / D converter 17 (see FIG. 2) by the DC offset cancellation function of the direct conversion receiver. Is done. Therefore, it is possible to reduce deterioration in reception performance due to harmonic noise of the clock signal used in the control unit 19 and the functional block.

  In addition, in one segment (terrestrial digital television broadcasting), it is expressed as “473−1 / 14 + (ch−13) × 6 to 473 + 5/14 + (ch−13) × 6 MHz (ch: integer of 13 to 62)”. Bands are used and each channel from 13 to 62 is set every 6 MHz. For example, the 13-channel band is approximately 472.9 to 473.4 MHz, and the 14-channel band is approximately 478.9 to 479.4 MHz. Focusing on the multiplication of 6 MHz here, the multiplication frequency in the vicinity of 13 channels is 468 MHz (78 times) or 474 MHz (79 times), and even the closest frequency from the 13 channel band is 0.6 MHz away, and the 6 MHz clock is When used, clock harmonics can be prevented from interfering within the 13-channel band. Since each channel of 13-62 of 1seg is set every 6 MHz, when a 6 MHz clock is used, the harmonics of the 6 MHz clock are 0.6 MHz away from the band in all bands. Therefore, in all one-segment bands, the harmonics of the 6 MHz clock can be prevented from interfering with the band, and when a 6 MHz clock is employed, the deterioration of the reception sensitivity of the one segment due to the harmonics of the clock is avoided. It is possible. An effective clock is not limited to 6 MHz but may be m × 6 MHz (m: integer). The 30.0 MHz clock satisfies the above-described conditions, and it is possible to avoid the deterioration of the one-segment reception sensitivity due to the harmonics of the clock.

  Furthermore, when a 30.0 MHz clock is used, it is within the 875-885 MHz, 1870-1880 MHz, and 2130-2150 MHz bands often used in W-CDMA (the band boundary frequency is not included in the band). In addition, it is possible to prevent the harmonics of the clock from interfering with each other. For this reason, in the cellular phone using the direct conversion mixer that supports the dual mode of the GSM system and the W-CDMA system, it is possible to reduce the deterioration of the reception performance due to the noise of the harmonics of the clock in both systems. . The above effects eliminate the need for magnetic sheet for suppressing high-frequency noise and shield materials such as filters, which were previously required for signal lines in the display unit, and can reduce the size, thickness, and cost of mobile phones. It becomes. Further, since it can be set to a high clock frequency, it can be applied to the enhancement of the functions of a mobile phone and the speeding up of signal processing.

It is a block diagram which shows the structure of the portable communication terminal which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structure of the receiving part of a direct conversion mixer system. It is explanatory drawing explaining the process which cancels DC offset by a DC cut capacitor. It is explanatory drawing explaining a process when signals other than a local oscillator signal interfere with a mixer input side as noise. It is explanatory drawing explaining the process which removes noise, when signals other than a local oscillator signal interfere on the mixer input side as noise. It is a block diagram which shows the structure of the portable communication terminal which concerns on Embodiment 2 of this invention. It is a block diagram which shows the structure of a general portable communication terminal.

Explanation of symbols

1 antenna, 2 antenna duplexer, 3 receiver, 4 transmitter, 5 signal processor,
6 microphone, 7 receiver, 8 operation unit, 9 control unit,
10 camera, 10a signal line of camera 10,
11 Display unit, 11a Signal line of display unit 11,
12 Direct conversion mixer,
13, 13a, 13b Reference oscillator,
14 filters, 15 amplifiers, 16 DC cut capacitors,
17 A / D converter, 18 local oscillator, 19 control unit, 20 memory,
21 Magnetic sheet for suppressing high-frequency noise, 22 Filter for suppressing high-frequency noise

Claims (7)

A direct conversion mixer that mixes a local oscillator signal set to a frequency that matches the center frequency of the reception channel of the desired signal with a high frequency desired signal received by the antenna, and a direct current component included in the output signal from the direct conversion mixer In a portable communication terminal including a receiving unit that converts a desired signal into a baseband signal, and an electronic component that is driven by a clock signal having a desired frequency.
A frequency of the clock signal supplied to the electronic component is set to a frequency at which a harmonic of the clock signal interferes with a center frequency of the reception channel. 2. The portable communication terminal according to claim 1, wherein the clock signal supplied to the electronic component uses an output signal of a reference oscillator serving as a reference of a local oscillator signal supplied to the direct conversion mixer. The clock signal supplied to the electronic component is generated by using a clock signal generating means that is newly generated with reference to the output signal of the reference oscillator serving as a reference of the local oscillator signal supplied to the direct conversion mixer. The mobile communication terminal according to claim 1 or 2. The mobile communication terminal according to any one of claims 1 to 3, wherein the clock signal is set to a frequency that is an integral multiple of a channel interval of the reception channel. The clock signal is set to a frequency represented by an integral multiple of 0.2 MHz, which is a channel interval of a reception channel, when performing communication using a GSM (Global System for Mobile communications) system. 4. The mobile communication terminal according to claim 1. The clock signal is set to a frequency represented by an integral multiple of 6 MHz when it has a function of receiving terrestrial digital television broadcasts. Mobile communication terminals. 6. The mobile phone according to claim 1, wherein when performing communication by a W-CDMA (Wideband Code Division Multiple Access) method, the clock signal is set to a frequency of 30.0 MHz. Communication terminal.

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