JP2010130328A - Television broadcast receiving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make an order of a filter low without reducing receiving sensitivity to attain miniaturization and cost reduction in a television broadcast receiving circuit built in a mobile communication terminal. <P>SOLUTION: The television broadcast receiving circuit 30 is provided with a bandwidth variable filter 31 between a low noise amplifier 12 and a variable amplifier circuit 15, and a BW control circuit 32 which switches filter characteristics of the bandwidth variable filter 31 by being synchronized with a channel selection signal. When a frequency of cellular phone transmitted wave and a broadcast receiving frequency are in combination for generating a spurious response, a first attenuation mode with a large attenuation amount is set by making a BW switching signal to be applied from the control circuit 32 to a transistor SW1 active. In addition, the frequency of the cellular phone transmitted wave and the broadcast receiving frequency are in combination for generating no spurious response, a second attenuation mode with a small attenuation amount is set by making the BW switching signal to be applied from the control circuit 32 to the transistor SW1 non-active. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a television broadcast receiving circuit built in a mobile communication terminal.

  With the increase in functionality of mobile phones, broadcast receivers have been installed in mobile phones. In a mobile phone equipped with a broadcast receiver, a filter for blocking the mobile phone transmission wave is installed in the front end of the broadcast receiver in order to eliminate interference with the broadcast receiver due to the transmission wave of the mobile phone ( For example, see Patent Document 1).

  FIG. 9A is a schematic diagram of a mobile phone equipped with a broadcast receiver, and FIG. 9B is a configuration diagram of a television broadcast receiving circuit in the broadcast receiver. A mobile transmitter unit 2 for generating a mobile phone transmission wave and a television broadcast receiving circuit 3 for receiving a television broadcast signal are installed in a casing of the mobile phone 1. The mobile transmitter unit 2 performs communication using a frequency band of a mobile phone transmission wave that is close to the low band side or the high band side of the television broadcast band.

  The television broadcast receiving circuit 3 passes the RF signal output from the antenna through a filter 11 made of BPF, extracts a broadcast band signal, inputs it to the low noise amplifier 12 and amplifies it, and then the frequency of the mobile phone transmission wave Input to the filter 13 for cutting the band. The filter 13 is composed of HPF when the frequency of the mobile phone transmission wave is located on the low band side of the broadcast band, and is composed of LPF when located on the high band side of the broadcast band. A broadcast band signal obtained by cutting the frequency band of the mobile phone transmission wave by the filter 13 is input to the tuner / control unit 14. The variable amplifier circuit 15 adjusts the level of the desired wave (reception channel) to adjust the received signal to an appropriate level. The mixer 16 multiplies the signal adjusted by the variable amplifier circuit 15 by a local oscillation signal supplied from the local oscillator 17 and converts the frequency into an IF signal. The IF signal output from the mixer 16 is amplified by an IF amplifier 18, demodulated by a demodulator 19, and further decoded by a decoding circuit 20 into a video signal and an audio signal. On the other hand, the demodulator output is branched and input to the AGC control circuit 21. The AGC control circuit 21 generates a gain control signal that makes the demodulated signal level constant, and supplies the gain control signal to the variable amplifier circuit 15 and the IF amplifier 18.

  There is gain suppression as a disturbance that the mobile phone transmission wave of the mobile transmitter unit 2 directly gives to the LNA 12 and the tuner / control unit 14 of the broadcast receiver 3. By installing the filter (BPF) 11 in front of the LNA 12, gain suppression of the LNA 12 due to strong mobile phone transmission power is prevented.

Further, there is a spurious response as an interference that the mobile phone transmission wave of the mobile transmitter unit 2 gives to the broadcast receiver unit 3. The mixer 16 is a circuit that generates an IF signal from the received wave and the local oscillation signal. In addition, the mixer 16 determines whether the IF signal is an integer multiple (m) of the incoming radio wave and an integer multiple (n) of the local oscillation signal frequency. Generate a signal. As shown in FIG. 10, during reception of the desired broadcast wave fr, if an incoming disturbing wave fu that matches the specific frequency condition is input to the mixer 16, the disturbing wave fu is converted to the same IF as the desired broadcast wave fr. Then, an IF signal including an interference wave is generated. Further, in the case of the direct conversion system that directly converts the received wave and the local oscillation signal to the baseband frequency, the interference wave fu is converted to the same baseband frequency as the desired broadcast wave fr, and the baseband signal including the interference wave is included. Is generated. In order to prevent a spurious response, it is necessary to attenuate the mobile phone transmission wave. Therefore, as shown in FIGS. 11A and 11B, a filter (LPF, HPF) 13 having a steep slope characteristic at the boundary between the broadcast band and the portable transmission band is installed to transmit the portable telephone transmission wave (arrival jamming wave). fu) is attenuated.
JP 2006-197450 A

  However, in order to sufficiently attenuate the mobile phone transmission wave (interference wave fu) by the filter 13, it is necessary to bring the attenuation pole closer to the broadcast reception wave band, and the attenuation of the signal in the broadcast reception wave band increases. There was a problem that the reception sensitivity of the broadcast wave was lowered. In addition, if a filter characteristic with a steep slope is realized by increasing the filter order in order to block mobile phone transmission waves, the circuit of the broadcast wave receiving unit becomes complicated and there is a problem of increasing the size.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a television broadcast receiving circuit that can reduce the order of the filter without lowering the receiving sensitivity and contribute to downsizing and cost reduction. And

  The television broadcast receiving circuit of the present invention is mounted on a mobile communication terminal having a mobile communication radio unit for mobile communication, and receives a broadcast wave of a television broadcast in a band different from the band used by the mobile communication radio unit. In a television broadcast receiving circuit, a frequency conversion circuit for mixing a local oscillation signal with a broadcast wave and converting it to a predetermined frequency including a baseband frequency, and having the broadcast wave in a pass band provided in a preceding stage of the frequency conversion circuit A filter having an attenuation band in the band of the mobile communication radio unit, the frequency of M times the transmission frequency of the mobile communication radio unit (M is a natural number) and N times the local oscillation signal (N is a natural number) When the signal generated by the difference from the frequency receives a channel that affects the predetermined frequency of the broadcast wave converted by the frequency conversion circuit, the signal passes through the filter. Frequency and the attenuation of the pass band and attenuation band which is closer to the band of the mobile communication radio unit of the attenuation band, characterized in that larger than the case of receiving the other channels.

  According to this configuration, when receiving a channel in which a spurious response occurs, the amount of attenuation of the band used by the mobile communication radio unit is increased to suppress interference, and when receiving other channels, the mobile communication By reducing the amount of attenuation in the pass band and attenuation band closer to the band used by the radio unit, the attenuation of the broadcast wave is reduced and the reception sensitivity is prevented from deteriorating.

  In the television broadcast receiving circuit according to the present invention, the filter switches a cut-off frequency based on a switching signal given in accordance with a reception channel to change the attenuation amount of the pass band and the attenuation band. And

  In the television broadcast receiving circuit, when the use band of the mobile communication radio unit is higher than the television broadcast signal band, the filter can be constituted by a low-pass filter.

  In the television broadcast receiving circuit, when the use band of the mobile communication radio unit is lower than the television broadcast signal band, the filter can be configured by a high-pass filter.

  The present invention is particularly effective when the order is low such that M is M = 2 and N is N = 3. Further, the present invention can be suitably applied when the mobile communication is cellular phone communication and the television broadcast is terrestrial digital television broadcast.

  According to the present invention, in a television broadcast receiving circuit that receives a broadcast wave by attenuating a mobile phone transmission wave, the order of the filter can be lowered without lowering the reception sensitivity, thereby realizing a reduction in size and price. be able to.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The television broadcast receiving circuit of this embodiment is built in a mobile communication terminal equipped with a portable transmitter.

  FIG. 1 is a configuration diagram of a television broadcast receiving circuit according to the present embodiment. In addition, the same code | symbol is attached | subjected to the same part as FIG.9 (b), and duplication of description is avoided. In the television broadcast receiving circuit 30, a variable bandwidth filter 31 is provided between the low noise amplifier 12 and the variable amplifier circuit 15. The tuner / control circuit 14 is provided with a BW control circuit 32 that switches the filter characteristics of the variable bandwidth filter 31 in synchronization with the channel selection signal. The BW control circuit 32 supplies a BW switching signal to the bandwidth variable filter 31 to switch the filter characteristics. The variable bandwidth filter 31 may be connected between the filter 11 and the low noise amplifier 12.

  In this embodiment, when the frequency of the mobile phone transmission wave and the broadcast reception frequency (reception channel) generate a spurious response, a filter characteristic for increasing the attenuation amount of the mobile phone transmission wave is set (“first In other combinations, the filter characteristic is switched to a filter characteristic with a small attenuation (referred to as “second attenuation mode”). The frequency of the mobile phone transmission wave is fixedly determined by the communication system (standardized communication method) adopted by the terminal, and the broadcast reception frequency dynamically changes according to the reception channel. When the communication system of the terminal is fixed, the reception channel to be set to the first attenuation mode can be determined in advance. The BW control circuit 32 controls the state (active / non-active) of the BW switching signal according to the reception channel.

  When the mobile phone transmission wave and the broadcast reception wave are close to each other, the broadcast frequency that generates a low-order spurious response does not exist in the entire broadcast band, but is limited to a low frequency range or a high frequency range. This is due to the fact that the predetermined frequency including the baseband frequency of the broadcast receiver built in the mobile phone is relatively low (around 500 KHz).

  When the broadcast wave is below the portable transmission wave, the frequency of the broadcast wave that generates a low-order spurious response is limited to the low frequency range of the broadcast wave. On the other hand, when the broadcast wave is above the portable transmission wave, the frequency of the broadcast wave that generates a low-order spurious response is limited to the high range of the broadcast wave.

  In Japan where the broadcast wave is below the mobile transmit wave, when the mobile phone transmit wave Fu is 815 to 925 MHz and the broadcast receive wave Fr is 470 to 770 MHz, the baseband frequency or IF frequency is 500 KHz, and Fu × 2 Considering a combination of Flocal = (Fr + IF) × 3, Fu × 2 = 1630 to 1850 MHz, and Flocal = (Fr + IF) × 3 = 1411.5 to 2311.5 MHz. From the overlapping range of the above two frequencies, the upper limit of the received broadcast wave that generates a spurious response of this combination is 1850 / 3−0.5 = 616.17 MHz. Therefore, broadcast reception waves that generate spurious responses exist only in the lower half. Therefore, if the first attenuation mode is selected only in the case of a broadcast reception wave that generates a spurious response (the lower half of the specific channel), it is possible to prevent deterioration in reception sensitivity in other reception channels.

  Even when the broadcast wave is above the mobile transmission wave, the broadcast reception wave that generates a low-order spurious response of Fu × 3 and Flocal × 2 with the same calculation method as when it is below the mobile transmission wave is Concentrate on high frequencies. Therefore, if the first attenuation mode is selected only in the case of a broadcast reception wave (a high-frequency specific channel) that generates a spurious response, it is possible to prevent deterioration in reception sensitivity in other reception channels.

There are also combinations of two waves that generate higher-order spurious responses, for example, Fu × 3 and Flocal × 4, and broadcast reception waves that generate spurious responses are not limited to half of the band. However, the reception interference due to the spurious response rapidly decreases as the order of both waves increases. Therefore, the performance requirement required for the filter is not high, and it is not necessary to switch the band of the filter.
FIG. 8 illustrates a combination of a mobile communication system and a UHF channel adopted in Japan, where a spurious response occurs or a spurious response may occur. As shown in the figure, a spurious response occurs in a specific channel in the lower half of the broadcast reception wave for one mobile communication system. Therefore, the first attenuation mode is set only when a reception channel that generates a spurious response is selected, and is returned to the second attenuation mode when other channels are received.

  FIG. 2 is a diagram showing the filter characteristics of the first attenuation mode and the second attenuation mode, and is a characteristic diagram when the broadcast reception band exists on the lower side of the portable transmission band. In this case, the variable bandwidth filter 31 can be configured with an LPF filter. The filter 11 is composed of a BPF whose pass band is the broadcast reception band.

  In the second attenuation mode, as shown by a solid line in FIG. 2, the cutoff frequency is kept away from the broadcast reception band to suppress the attenuation of the broadcast reception signal.

  In the first attenuation mode, as shown by a dotted line in FIG. 2, the cutoff frequency is kept away from the portable transmission band, and the attenuation of the portable transmission signal is increased.

  FIG. 3 is a diagram showing the filter characteristics of the first attenuation mode and the second attenuation mode, and is a characteristic diagram when the broadcast reception band exists on the high frequency side of the portable transmission band. In this case, the variable bandwidth filter 31 can be configured with an HPF filter. The filter 11 is composed of a BPF whose pass band is the broadcast reception band.

  In the second attenuation mode, as shown by a solid line in FIG. 3, the cutoff frequency is kept away from the broadcast reception band to suppress the attenuation of the broadcast reception signal.

  In the first attenuation mode, as shown by a dotted line in FIG. 3, the cutoff frequency is kept away from the portable transmission band to increase the attenuation of the portable transmission signal.

  As described above, when the frequency of the mobile phone transmission wave and the broadcast reception frequency (reception channel) generate a spurious response, switching to the first attenuation mode to increase the attenuation of the mobile transmission signal causes the mobile interference. Suppress the wave. Further, in the case of a combination in which spurious response does not occur or does not substantially cause a problem, switching to the second attenuation mode suppresses the attenuation amount of the broadcast reception signal and prevents the reception sensitivity from deteriorating.

Next, the circuit configuration of the variable bandwidth filter 31 composed of LPF will be described.
FIG. 4A is an equivalent circuit diagram of the variable bandwidth filter 31 configured with a third-order T-type LPF. Inductors L1 and L3 are connected in series between the input end and the output end, and a series resonant circuit including an inductor L2 and a capacitor C1 is connected between the connection point of the inductors L1 and L3 and the ground. A capacitor C2 is connected in parallel to the capacitor C1. The capacitor C2 has a ground-side terminal connected to the ground through the collector-emitter of the transistor SW1 in series. A BW switching signal is applied to the base of the transistor SW1 from the BW control circuit 32 via the bias resistor R1. When the transistor SW1 is ON, the capacitor C2 is connected in parallel. When the transistor SW1 is OFF, the ground-side terminal of the capacitor C2 is open. Therefore, the additional capacity of the resonance circuit changes due to ON / OFF of the transistor SW1, and the resonance frequency changes.

  FIG. 4B is an equivalent circuit diagram of the variable bandwidth filter 31 configured with a fifth-order T-type LPF. Inductors L1, L3, and L5 are connected in series between the input end and the output end, and a second resonance circuit including the inductor L2 and the capacitor C1 is connected between the connection point of the inductors L1 and L3 and the ground. A first resonance circuit including an inductor L4 and a capacitor C4 is connected between the connection point of the inductors L3 and L5 and the ground. A capacitor C3 is connected in parallel to the capacitor C4, and the capacitor C3 can be connected or disconnected by turning ON / OFF the transistor SW1.

  FIGS. 5A and 5B are diagrams showing filter characteristics of the bandwidth variable filter 31 configured by the third-order T-type LPF shown in FIG. The capacitance of the resonance circuit composed of the inductor L1 and the capacitor C1 is 2.7 pF, and when the transistor SW1 is turned on, the sum of the equivalent capacitances of the capacitor C2 and the transistor SW1 is 1.2 pF.

  FIG. 5A is a diagram showing filter characteristics when the transistor SW1 is turned off and the capacitance of the resonance circuit is 2.7 pF. An attenuation pole exists in the vicinity of 1.0 GHz. FIG. 5B is a diagram showing the filter characteristics when the transistor SW1 is turned on and the combined capacitance of the resonance circuit is (2.7 pF + 1.2 pF). By adding the additional capacitance, the attenuation pole and the passband are moved to a lower frequency.

  6A and 6B are diagrams showing the filter characteristics of the bandwidth variable filter 31 configured by the fifth-order T-type LPF shown in FIG. 4B. The attenuation pole of the first resonance circuit consisting of the inductor L4 + capacitors C4 and C3 is M1, and the attenuation pole of the second resonance circuit consisting of the inductor L2 + capacitor C1 is M2. The capacitance of C4 is set to 3.0 pF, and when the transistor SW1 is turned on, the sum of the equivalent capacitances of the capacitor C3 and the transistor SW1 is set to 0.9 pF.

  FIG. 6A is a diagram illustrating filter characteristics when the transistor SW1 is turned off and the capacitance of the first resonance circuit is set to 3.0 pF. The attenuation pole M1 of the first resonance circuit exists in the vicinity of 0.9 GHz. FIG. 6B is a diagram showing filter characteristics when the transistor SW1 is turned on and the combined capacitance of the first resonance circuit is (3.0 pF + 0.9 pF). By adding the additional capacitor, the attenuation pole M1 and the pass band of the first resonance circuit are moved to a lower frequency. The attenuation pole M2 of the second resonance circuit does not move even when the capacitance changes.

  FIG. 7A is an equivalent circuit diagram of the variable bandwidth filter 31 configured with a third-order T-type HPF. Capacitors C5 and C7 are connected in series between the input terminal and the output terminal, and a resonance circuit including an inductor L6 and a capacitor C6 is connected between a connection point between the capacitor C5 and the capacitor C7 and the ground. A capacitor C8 is connected in parallel to the capacitor C6, and is connected to the ground via the collector-emitter of the transistor SW1. A BW switching signal is applied to the base of the transistor SW1.

  FIG. 7B is an equivalent circuit diagram of the variable bandwidth filter 31 configured with a fifth-order T-type HPF. Capacitors C5, C7, and C9 are connected in series between the input end and the output end, and a resonance circuit including an inductor L7 and a capacitor C10 is connected between a connection point between the capacitors C7 and C9 and the ground. Yes. A capacitor C11 is connected in parallel to the capacitor C10, and is connected to the ground via the collector-emitter of the transistor SW1. A BW switching signal is applied to the base of the transistor SW1.

  The filter characteristics can be switched between the first attenuation mode and the second attenuation mode by the BW switching signal applied to the base of the transistor SW1 also by the HPF configured as described above.

  Thus, according to the present embodiment, in the case of a combination in which the frequency of the mobile phone transmission wave and the broadcast reception frequency generate a spurious response, the BW switching signal applied from the control circuit 32 to the transistor SW1 is set as active. 1 Decay mode is set. In the case where the frequency of the mobile phone transmission wave and the broadcast reception frequency do not generate a spurious response, the BW switching signal applied from the control circuit 32 to the transistor SW1 is set inactive to set the second attenuation mode. As a result, when operating with a combination of a mobile phone transmission wave and a broadcast reception wave that generates a large spurious response disturbance, the filter pole and passband can be moved, so that the filter order can be reduced without reducing the reception sensitivity. It can be reduced, and can contribute to downsizing and cost reduction.

  In the above description, the mixer 16 generates the IF signal from the received wave and the local oscillation signal. However, the present invention can also be applied to a direct conversion method that directly converts to the baseband frequency instead of the IF.

  The present invention is applicable to a mobile phone equipped with a broadcast receiver.

1 is a configuration diagram of a television broadcast receiving circuit according to an embodiment of the present invention. The figure which shows the filter characteristic of the 1st attenuation | damping mode of a variable bandwidth filter comprised by LPF, and a 2nd attenuation | damping mode The figure which shows the filter characteristic of the 1st attenuation | damping mode and 2nd attenuation | damping mode of the bandwidth variable filter comprised by HPF (A) Equivalent circuit diagram of variable bandwidth filter configured with third-order T-type LPF, (b) Equivalent circuit diagram of variable bandwidth filter configured with fifth-order T-type LPF (A) The figure which shows the filter characteristic before the parallel capacity | capacitance addition of the bandwidth variable filter comprised by the 3rd-order T type LPF, (b) The figure which shows the filter characteristic at the time of the parallel capacity addition of the same bandwidth variable filter (A) The figure which shows the filter characteristic before the parallel capacity | capacitance addition of the bandwidth variable filter comprised with 5th-order T type LPF, (b) The figure which shows the filter characteristic at the time of the parallel capacity addition of the same bandwidth variable filter (A) Equivalent circuit diagram of variable bandwidth filter configured with third-order T-type HPF, (b) Equivalent circuit diagram of variable bandwidth filter configured with fifth-order T-type HPF The figure which shows the combination of the mobile communication system which a spurious response generate | occur | produces, and a UHF channel (A) Schematic diagram of a mobile phone equipped with a broadcast receiver, (b) Configuration diagram of a television broadcast receiver circuit in the broadcast receiver Diagram for explaining the generation principle of spurious response (A) Filter characteristic diagram when the broadcast wave is below the portable transmission wave, (b) Filter characteristic diagram when the broadcast wave is above the portable transmission wave

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mobile phone 2 ... Portable transmitter part 11 ... Filter (BPF)
12 ... Low noise amplifier 13 ... Filter (LPF, HPF)
DESCRIPTION OF SYMBOLS 15 ... Variable amplifier circuit 16 ... Mixer 17 ... Local oscillator 18 ... IF amplifier 19 ... Demodulator 20 ... Decoding circuit 21 ... AGC control circuit 30 ... Television broadcast receiving circuit 31 ... Variable bandwidth filter 32 ... BW control circuit

Claims (6)

In a television broadcast receiving circuit that is mounted on a mobile communication terminal having a mobile communication radio unit for mobile communication and receives a broadcast wave of a television broadcast in a band different from the use band of the mobile communication radio unit,
A frequency conversion circuit that mixes a local oscillation signal with a broadcast wave and converts it to a predetermined frequency including a baseband frequency, and is provided in a preceding stage of the frequency conversion circuit and has the broadcast wave in a passband, and the mobile communication radio unit With a filter with an attenuation band in the band,
A signal generated by the difference between a frequency M times the transmission frequency of the mobile communication radio unit (M is a natural number) and a frequency N times the local oscillation signal (N is a natural number) is converted by the frequency conversion circuit. When receiving a channel that affects the predetermined frequency of the broadcast wave, the amount of attenuation in the passband and attenuation region that is closer to the use band of the mobile radio unit out of the passband and attenuation region of the filter is A television broadcast receiving circuit characterized in that it is larger than the case of receiving a channel other than.   The television broadcast receiving circuit according to claim 1, wherein the filter changes the attenuation amount of the pass band and the attenuation band by switching the cut-off frequency based on a switching signal given in accordance with a reception channel.   3. The television broadcast receiving circuit according to claim 1, wherein a use band of the radio unit for mobile communication is higher than a television broadcast signal band, and the filter is constituted by a low-pass filter.   3. The television broadcast receiving circuit according to claim 1, wherein a use band of a radio unit for mobile communication is lower than a television broadcast signal band, and the filter is a high-pass filter.   3. The television broadcast receiving circuit according to claim 2, wherein M is M = 2 and N is N = 3.   6. The television broadcast receiving circuit according to claim 1, wherein the mobile communication is a mobile phone communication, and the television broadcast is a terrestrial digital television broadcast.

Images