JP2008227824A - Reception circuit and communication device - Google Patents

Abstract

An object of the present invention is to provide a receiving circuit and a communication device in which the center frequency of an RF filter and an LO filter is unlikely to vary even when circuit characteristics vary.
A phase comparison circuit compares a phase of a signal input to an LO filter circuit and a signal output from the LO filter circuit and outputs a signal indicating a phase difference. The frequency setting circuit 105 generates a control signal for adjusting the tuning frequency of the RF filter circuit 110 and the LO filter circuit 120 based on the signal from the phase comparison circuit 104, and supplies the control signal to both the RF filter circuit 110 and the LO filter circuit 120. Is output. The control signal is generated based on the phase difference indicated by the signal from the phase comparison circuit 104 so that the center frequency is held at a predetermined value in the RF filter circuit 110 and the LO filter circuit 120.
[Selection] Figure 2

Description

  The present invention relates to a receiving circuit that performs frequency conversion on an RF signal based on a local oscillation signal, and a communication apparatus including the receiving circuit.

  One of the causes of noise generated in the receiving apparatus is the cross modulation characteristic of the receiving apparatus. One of the optimum methods for improving the cross modulation characteristic is to improve the frequency selectivity of a received RF (Radio Frequency) signal. For example, in a receiving device for a TV tuner, channel assignments from VHF (Very High Frequency) to UHF (Ultra High Frequency) are wide. For this reason, when selecting a desired channel, the RF filter circuit limits the band to improve the frequency selectivity.

  A number of methods for performing frequency selection in accordance with a desired channel in an RF filter circuit have been proposed. For example, in Patent Document 1, an RF filter circuit has a function of frequency adjustment, and a control signal is input to the RF filter circuit to adjust to a desired channel.

  On the other hand, in Patent Document 1, an LO (Local Oscillator) filter circuit is further provided in addition to the RF filter circuit. That is, the RF filter circuit performs frequency selection on the RF signal, and the LO filter circuit also performs frequency selection on the LO signal. Since the LO filter circuit suppresses spurious noise and harmonic noise generated in the local oscillation signal, it is effective in suppressing noise when receiving a desired channel. The LO filter circuit of Patent Document 1 also has a function of frequency adjustment. FIG. 7 shows a circuit configuration of Patent Document 1 having such an RF filter circuit and an LO filter circuit.

  The circuit in FIG. 7 includes an RF filter circuit 901, an LO filter circuit 903, a mixer circuit 902, a control unit 906, and variable voltage circuits 904 and 905. An RF signal is input to the RF filter circuit 901, and an LO signal from a local signal transmitter (not shown) is input to the LO filter circuit 903. The mixer circuit 902 generates an intermediate frequency signal from the signals input from the LO filter circuit 903 and the RF filter circuit 901. The variable voltage circuits 904 and 905 convert the signal from the control unit 906 into voltage signals that match the RF filter circuit 901 and the LO filter circuit 903, respectively, and output them to these filter circuits. That is, in the circuit of FIG. 7, the variable voltage circuits 904 and 405 convert a signal matched with a desired channel in the control unit 906 into a control signal voltage to be supplied to the RF filter circuit 901 and the LO filter circuit 903. Thus, each of the RF filter circuit 901 and the LO filter circuit 903 is adjusted to a frequency corresponding to a desired channel.

Japanese Patent Laid-Open No. 10-41844

  On the other hand, in order to select a desired channel frequency in the RF filter circuit and the LO filter circuit, it is necessary to set the tuning frequency of these filter circuits. According to the circuit configuration of FIG. 7, it is necessary to match the center frequency of the RF filter circuit 901 or the LO filter circuit 903 with the frequency of the local signal oscillator that generates the LO signal. The control unit 906 outputs a control signal for each filter circuit according to a preset frequency of the local signal oscillator, thereby controlling the center frequency of the limited band in the RF filter circuit 901 and the LO filter circuit 903.

  However, in the RF filter circuit 901 and the LO filter circuit 903, the circuit constants of the filter circuit may vary due to process variations in circuit characteristics and environmental variations such as temperature. If the circuit constant varies, the center frequency of the limited band may fluctuate in the filter circuit. According to the configuration of FIG. 7, since the control signal is generated according to a preset value, there is a problem that it is difficult to cope with the above frequency fluctuation.

  An object of the present invention is to provide a receiving circuit and a communication device in which the center frequency of an RF filter and an LO filter is less likely to vary due to variations in circuit characteristics.

Means and effects for solving the problems

  The receiving circuit of the present invention includes an RF filter circuit that limits an RF (Radio Frequency) signal to a first frequency band based on a first tuning frequency, and a second local oscillation signal based on a second tuning frequency. A local oscillation filter circuit limited to a frequency band, first and second frequency changing means for changing the first and second tuning frequencies, respectively, and the RF filter circuit based on a signal from the local oscillation filter circuit A mixer circuit that performs a frequency conversion process on the signal from the local oscillation signal, a local oscillation signal before the local oscillation filter circuit limits to the second frequency band, and the local oscillation filter circuit limited to the second frequency band A phase comparison circuit that generates a signal indicating a phase difference from a subsequent local oscillation signal, and the RF filter based on the signal generated by the phase comparison circuit And a control means for controlling said first and second frequency changing means so that the center frequency of the first and second frequency bands in the road and the local oscillation filter circuit is respectively maintained at a predetermined value.

  According to the receiving circuit of the present invention, even if a frequency fluctuation due to a variation in circuit characteristics or the like occurs in the local oscillation (LO) filter circuit, the phase comparison circuit can grasp the degree of the frequency fluctuation. The control means controls the tuning frequency so that the frequencies of the RF filter circuit and the local oscillation filter circuit are kept constant according to the degree of frequency fluctuation. Therefore, even when there are variations in circuit characteristics and environmental fluctuations such as temperature, fluctuations in the center frequency of the limited band are suppressed in each filter circuit. Further, since it is sufficient to provide the phase comparison circuit only in the local oscillation filter circuit, the configuration can be simplified. Note that the local oscillation filter circuit can suppress spurious noise and harmonic noise generated in the local oscillation signal, and can suppress noise during reception of a desired channel.

  Moreover, in this invention, it further has an input part into which the upper limit signal and the lower limit signal which respectively show the upper limit and the lower limit of the said 1st and 2nd tuning frequency are input, The said control means is from the said input part. Preferably, the first and second frequency changing means are controlled based on the upper limit signal and the lower limit signal. According to this configuration, even when the tuning frequency is greatly changed, the frequency can be finely adjusted after roughly adjusting the frequency in advance. Therefore, it is possible to prevent the tuning frequency from being greatly shifted.

  In the present invention, the first and second amplitude changing means for changing the amplitudes of the output signals from the RF filter circuit and the local oscillation filter circuit, respectively, and the local oscillation filter circuit in the second frequency band. An amplitude reference circuit that generates a signal indicating the amplitude of the limited local oscillation signal, and the control means is based on the signal generated by the amplitude reference circuit and the signal generated by the phase comparison circuit. In the RF filter circuit and the local oscillation filter circuit, the center frequencies of the first and second frequency bands are held at predetermined values, respectively, and the amplitudes of the RF signal and the output signal from the local oscillation filter circuit are predetermined. It is preferable to control the first and second frequency changing means and the first and second amplitude changing means so that the values are held. For example, when the RF filter circuit and the LO filter circuit are configured so that the frequency can be changed by a variable capacitor such as a varactor diode, the gain of the filter circuit may change depending on the frequency. According to the above configuration, since adjustment is performed so as to keep the amplitude constant, fluctuations in amplitude when the gain of the filter circuit changes can be suppressed. In addition, since the amplitude is adjusted even if the amplitude of the local oscillation signal varies due to process variations of circuit characteristics and environmental variations such as temperature, sufficient performance can be given to band limitation of the RF filter circuit. Further, since it is sufficient to provide the amplitude comparison circuit only in the local oscillation filter circuit, the configuration can be simplified.

  In the present invention, it is preferable that both the RF filter circuit and the local oscillation filter circuit are band pass filter circuits. According to this configuration, an interference signal other than the desired channel frequency can be suppressed in the RF filter circuit. Further, since the spurious noise and the harmonic noise generated in the local oscillation signal are suppressed in the local oscillation filter circuit, it is effective for noise suppression when receiving a desired channel.

  In the present invention, the RF filter circuit and the local oscillation filter circuit have the same circuit configuration, and the control means outputs the same control signal to each of the first and second frequency changing means. It is preferable. According to this configuration, since the same control signal is output to any filter circuit, the circuit configuration is simplified. For example, when the direct conversion method is adopted, the RF filter circuit and the local oscillation filter circuit can be realized by a circuit having the same configuration and the same set value.

  By the way, in the case where the double conversion method is adopted or when the RF signal and the local oscillation signal are in different frequency bands as in the case where the Low-IF (Intermediate Frequency) method is adopted, Only values such as L and C that determine the tuning frequency of the RF filter circuit and the local oscillation filter circuit need only be shifted from each other, and other circuit configurations can be configured identically.

  The present invention further includes a local oscillator that outputs a local oscillation signal to the local oscillation filter circuit, wherein the RF filter circuit, the local oscillation filter circuit, the phase comparator, the mixer circuit, and the local oscillation circuit are provided. These are preferably constructed on the same substrate. This configuration leads to a reduction in the number of external parts and can contribute to the miniaturization of parts.

  In the present invention, it is preferable that both the RF filter circuit and the local oscillation filter circuit are constituted by an L-C filter including a negative resistance circuit. According to this configuration, the Q of the LC filter is increased by including the negative resistance circuit.

  The receiving circuit of the present invention is applicable to various communication devices such as a mobile phone and a digital image receiving device. By applying the receiving circuit of the present invention to these communication apparatuses, a communication apparatus having high communication performance in which a decrease in frequency selectivity due to process variations in the receiving circuit is suppressed is realized.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a schematic configuration of a receiving apparatus 1000 according to the first embodiment.

[First Embodiment]
The receiving apparatus 1000 includes a tuner unit 100, a demodulation unit 700, and a data processing unit 800. An RF signal received from an antenna or the like is input to the tuner unit 100. The tuner unit 100 performs a channel selection process on the input RF signal and outputs it to the demodulation unit 700. Demodulation section 700 performs demodulation processing on the signal that has been subjected to channel selection processing, demodulates it into a data string signal, and outputs it to data processing section 800. The data processing unit 800 executes various data processing based on the data string signal. For example, a process for reproducing the image, sound, and characters indicated by the data string signal is executed.

  FIG. 2 is a diagram illustrating a configuration of a circuit (receiving circuit) that performs channel selection processing in the tuner unit 100. Such a circuit configuration includes an RF filter circuit 110, an LO filter circuit 120, and a mixer circuit 102. The circuit configurations of these circuits are all constructed on the same substrate.

  An RF signal is input to the RF filter circuit 110 via the input terminal I1. The RF filter circuit 110 outputs the input RF signal by limiting it to a predetermined frequency band (first frequency band). An LO signal is input to the LO filter circuit 120 via the input terminal I2. This LO signal is generated in a local oscillator (not shown) such as a voltage controlled oscillator (VCO). Alternatively, the local oscillator may be input to the input terminal I2 through a frequency divider. The LO filter circuit 120 limits the input LO signal to a predetermined frequency band (second frequency band) and outputs it. The mixer circuit 102 performs frequency conversion on the RF signal whose band is limited by the RF filter circuit 110 based on the signal from the LO filter circuit 120, and outputs the result via the output terminal O1.

  In this embodiment, it is assumed that the direct conversion method is adopted for the receiving circuit. Therefore, the center frequency of the LO signal is set to the same magnitude as the center frequency of the desired channel. The RF filter circuit 110 and the LO filter circuit 120 have the same circuit configuration.

  The RF signal may include a wide band frequency other than a desired frequency such as an interference wave. By providing the RF filter circuit 110, frequencies other than a desired frequency such as an interference wave are removed, and the frequency selectivity is improved with respect to the frequency of the desired channel. Further, by providing the LO filter circuit 120, the frequency selectivity regarding the frequency of the desired channel is further improved.

  2 has a phase comparison circuit 104 and a frequency setting circuit (control means) 105. The LO signal is input to the phase comparison circuit 104 via the input terminal I2, and the output signal from the LO filter circuit 120 is input. Then, the phases of the input signals are compared. That is, the phase comparison circuit 104 compares the phase of the LO signal before the LO filter circuit 120 limits the frequency band and the phase of the LO signal after the LO filter circuit 120 limits the frequency band. The phase comparison circuit 104 outputs a signal indicating the result of phase comparison to the frequency setting circuit 105. The frequency setting circuit 105 generates a control signal for controlling the tuning frequency (described later) of the RF filter circuit 110 and the LO filter circuit 120 based on the signal from the phase comparison circuit 104. The generated control signal is output to the RF filter circuit 110 and the LO filter circuit 120, respectively. The RF filter circuit 110 and the LO filter circuit 120 are configured to change the tuning frequency based on a control signal from the frequency setting circuit 105.

  FIG. 3 shows a more detailed configuration of the RF filter circuit 110 and the LO filter circuit 120. As described above, in the present embodiment, it is assumed that the direct conversion method is adopted. Therefore, the RF filter circuit 110 and the LO filter circuit 120 have the same circuit configuration. That is, FIG. 3 shows a configuration common to both filter circuits. Hereinafter, the configuration of the RF filter circuit 110 will be described.

  The RF filter circuit 110 includes a gm circuit 112, a variable inductor 113, a capacitor 114, and a resistor 115. A voltage signal corresponding to the RF signal is input to the gm circuit 112 via the input terminal I3. The gm circuit 112 converts the input voltage into a current and outputs the current. In the case of the LO filter circuit 120, a voltage signal corresponding to the LO signal is input. The variable inductor 113, the capacitor 114, and the resistor 115 are connected in parallel to each other. The current output from the gm circuit 112 is input to one end of these parallel connections. The other end of the parallel connection is grounded. The current input to the variable inductor 113, the capacitor 114, and the resistor 115 is converted into a voltage signal by these combined loads, and is output to the mixer circuit 102 via the output terminal O2.

  As described above, the RF filter circuit 110 and the LO filter circuit 120 are LC band-pass filters that can change the inductor value. That is, the RF filter circuit 110 and the LO filter circuit 120 are provided with variable inductors, whereby the tuning frequencies (first and second tuning frequencies) are changed (changing means). The inductor value of the variable inductor 113 is controlled based on a control signal from the frequency setting circuit 105. When the inductor value of the variable inductor 113 is L, the capacitance value of the capacitor 114 is C, and the resistance value of the resistor 115 is R, the transfer function of the LC filter of FIG. 3 is expressed as follows. Note that s = jω.

  In the above configuration, the control signal of the frequency setting circuit 105 is adjusted so that the center frequency of the band limited by the RF filter circuit 110 and the LO filter circuit 120 is maintained at a predetermined value, that is, the frequency of the local oscillation signal. Specifically, the frequency setting circuit 105 reduces the tuning frequency based on the signal from the phase comparison circuit 104 when the phase of the signal from the input terminal I2 is ahead of the phase from the LO filter circuit 120. Such a control signal is output. On the other hand, when the phase of the signal from the input terminal I2 is delayed from the phase from the LO filter circuit 120, a control signal that increases the tuning frequency is output.

  This prevents frequency shift when the LO filter circuit 120 limits the band of the LO signal. On the other hand, the same control signal as the LO filter circuit 120 is also input to the RF filter circuit 110 from the frequency setting circuit 105. As described above, since the RF filter circuit 110 has the same circuit configuration as the LO filter circuit 120, deviation from the LO signal is avoided even at the center frequency of the limited band of the RF filter circuit 110, and is maintained at a predetermined value. Is done.

  With the above configuration, in the first embodiment, temperature fluctuations, process variations, and variations occurring for each circuit configuration of the filter are suppressed, and the center frequency of the limited band in the filter is held at a predetermined value at a desired channel frequency. It becomes possible.

  In the above configuration, by changing L, the tuning frequency is adjusted to be constant regardless of temperature fluctuations and process variations. On the other hand, the constant tuning frequency substantially corresponds to the LC being kept constant. Therefore, T (ω0) when the tuning frequency is ω0 is kept constant according to the above equation 1. In other words, in the first embodiment, the gain is also kept constant by adjusting the tuning frequency to be constant.

  It is preferable that a signal indicating the upper limit value and the lower limit value of the tuning frequency is input via the input terminal 106 of FIG. For example, the frequency setting circuit 105 first adjusts the tuning frequencies of the RF filter circuit 110 and the LO filter circuit 120 to a range indicated by the signal from the input terminal 106 based on the signal from the input terminal 106. Here, the signal from the input terminal 106 indicates an upper limit value and a lower limit value that are calculated in advance so that the band limitation corresponding to a desired channel is performed in the filter circuit. Next, the frequency setting circuit 105 adjusts the tuning frequencies of the RF filter circuit 110 and the LO filter circuit 120 in detail as described above based on the signal from the phase comparison circuit 104. The receiving apparatus 1000 preferably has such a configuration.

  For example, a television tuner receives a VHF signal or a UHF signal, and the tuning frequency changes greatly. According to the above configuration, even when the tuning frequency is greatly changed in this way, fine adjustment is performed after the frequency is roughly adjusted in advance. Therefore, a significant shift in the tuning frequency is suppressed, and a malfunction due to the setting of the tuning frequency by the phase comparison circuit 104 and the frequency setting circuit 105 is suppressed.

[Second Embodiment]
Hereinafter, the second embodiment will be described with reference to FIGS. 4 and 5. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The second embodiment is obtained by replacing the circuit configuration of FIG. 2 with the circuit configuration of FIG. 4 in the first embodiment. Also in the second embodiment, a direct conversion method is assumed. The reception circuit in FIG. 4 includes an RF filter circuit 210 and an LO filter circuit 220. These circuit configurations are the same. The RF filter circuit 210 and the LO filter circuit 220 have a configuration capable of adjusting the amplitude of the output signal while adjusting the tuning frequency as will be described later.

  The reception circuit in FIG. 4 includes a phase comparison circuit 104 and a frequency setting circuit 105. The phase comparison circuit 104 outputs a signal indicating the phase difference between the output signal of the LO filter circuit 210 and the LO signal input via the input terminal I2 to the frequency setting circuit 105. The frequency setting circuit 105 outputs a control signal for controlling the tuning frequency to the RF filter circuit 210 and the LO filter circuit 220 based on the signal from the phase comparison circuit 104. As a result, similarly to the first embodiment, the tuning frequency is adjusted in these filter circuits also in the second embodiment.

  The receiving circuit of FIG. 4 is further provided with an amplitude reference circuit 206 and an amplitude setting circuit 207. The output signal from the LO filter circuit 220 is input to the amplitude reference circuit 206. The amplitude reference circuit 206 generates a signal indicating the amplitude of the input signal and outputs the signal to the amplitude setting circuit 207. Based on the amplitude indicated by the output signal from the amplitude reference circuit 206, the amplitude setting circuit 207 generates a control signal that makes the amplitude of the output signal of the LO filter circuit 220 constant. The control signal is output to the RF filter circuit 210 together with the LO filter circuit 220.

  FIG. 5A is a diagram illustrating a detailed circuit configuration of the RF filter circuit 210 and the LO filter circuit 220. The RF filter circuit 210 and the LO filter circuit 220 have the same circuit configuration. Hereinafter, the configuration of the RF filter circuit 210 will be described.

  The RF filter circuit 210 includes a gm circuit 112, an inductor 213, a variable capacitor 214, and a variable resistor 215. The inductor 213 has an inductor component having an inductor value L and a series resistance component having a resistance value r. The variable capacitor 214 is composed of, for example, a varactor diode.

  A voltage signal corresponding to the RF signal is input to the gm circuit 112 via the input terminal I4. The gm circuit 112 converts the input voltage into a current and outputs the current. Note that a voltage signal corresponding to the LO signal is input to the LO filter circuit 220. The inductor 213, the variable capacitor 214, and the variable resistor 215 are connected in parallel to each other. The current output from the gm circuit 112 is input to one end of these parallel connections. The other end of the parallel connection is grounded. The currents input to the inductor 213, the variable capacitor 214, and the variable resistor 215 are converted into voltage signals by these combined loads and output to the mixer circuit 102 via the output terminal O3. Thus, the RF filter circuit 210 and the LO filter circuit 220 are LC band-pass filters in which the Q of the filter is increased by adding the variable resistor 215 as a negative resistance circuit.

  When the capacitance value of the variable capacitor 214 is C and the resistance value of the variable resistor 215 is R, the transfer function of the RF filter circuit 210 is expressed as follows. Note that s = jω.

  Then, the gain at the time of tuning when it is assumed that R >> r, that is, when Formula 3 is satisfied, is expressed as Formula 4.

Therefore, the transfer function during tuning depends on C. That is, when the value of C is changed in order to adjust the tuning frequency ω ₀ , the gain varies.

  Therefore, in the above configuration, the amplitude setting circuit 207 compares the amplitude indicated by the signal from the amplitude reference circuit 206 with a predetermined value. When the amplitude exceeds a predetermined value, a control signal indicating that the amplitude is decreased is generated. When the amplitude is lower than the predetermined value, a control signal indicating that the amplitude is increased is generated, and the RF filter is generated. Output to the circuit 210 and the LO filter circuit 220.

The RF filter circuit 210 and the LO filter circuit 220 increase or decrease the gain by changing the resistance of the variable resistor 215 based on the control signal from the amplitude setting circuit 207 (first and second amplitudes). Change means). Even if T (ω ₀ ) changes by adjusting the tuning frequency in this way, the RF filter circuit 210 and the LO filter circuit 220 change the resistance value of the variable resistor 215 in accordance with the change, so that T ( Correction is performed so that the value of ω ₀ ) is held at a predetermined value.

  With the above configuration, in the second embodiment, temperature fluctuations, process variations, and variations occurring for each circuit configuration of the filter are suppressed, and the center frequency of the limited band in the filter is held at a predetermined value at a desired channel frequency. This makes it possible to make the gain of the filter constant.

Furthermore, in order to adjust the tuning frequency of the RF filter circuit 210 and the like so that the band ω _b expressed by the following formula 5 becomes constant, the magnitude of C is changed and the tuning frequency ω ₀ is adjusted. At the same time, the magnitude of R may be changed so that the value of ω _b is constant. Further, the gm value of the gm circuit 112 may be changed in order to make the gain constant.

  FIG. 5B shows a circuit configuration of an RF filter circuit 210 ′ and an LO filter circuit 220 ′, which are modifications of the RF filter circuit 210 and the LO filter circuit 220. The RF filter circuit 210 'and the LO filter circuit 220' have the same circuit configuration. The RF filter circuit 210 ′ and the LO filter circuit 220 ′ show a configuration in which the value of r is small and the Q value of the inductor can be used as it is for the Q of the bandpass filter. Therefore, the variable resistor 215 is not provided in the filter circuit of FIG. In the filter circuit of FIG. 5B, the transfer function is expressed as follows.

  Therefore, the gain at the time when the formula 3 is established is expressed as follows.

Also in this case, if the value of C is changed in order to adjust the tuning frequency ω ₀ , the gain at the time of tuning changes. Therefore, when the RF filter circuit 210 ′ and the LO filter circuit 220 ′ are used, the gm value of the gm circuit 112 is set so that the gain at the time of tuning is constant, that is, the value of T (ω ₀ ) is constant. It is preferable that the receiving apparatus 1000 has a configuration that corrects by changing the above.

<Other variations>
The above is a description of a preferred embodiment of the present invention. However, the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope described in the means for solving the problem. It can be changed.

  For example, in the first and second embodiments described above, the RF signal is transferred from the input terminal to the mixer circuit through the RF filter circuit. However, a separate RF amplifier circuit may be provided before the RF filter circuit or between the RF filter circuit and the mixer circuit. For example, in the circuit of FIG. 6A, the RF signal is delivered to the mixer circuit 102 through the RF amplifier circuit 501 and the RF filter circuit 110 in order. In the circuit of FIG. 6B, the RF signal is delivered to the mixer circuit 102 through the RF filter circuit 110 and the RF amplifier circuit 501 in order.

  In the above-described second embodiment, either of the resistor 215 and the gm circuit 112 may be made variable so that a constant gain during tuning may be realized, or both the resistor 215 and the gm circuit 112 may be made variable. By doing so, the gain may be adjusted.

  In the above-described embodiment, all the constituent circuits such as the inductor, the capacitor, the resistor, and the transistor in the receiving circuit are configured on the same substrate. However, it may be configured on another substrate. In the above embodiment, a tuning frequency variable mechanism is realized using a variable inductor or a variable capacitor manufactured by a gyrator or the like. However, any configuration can be used as long as the tuning frequency can be changed. May be.

  In the first and second embodiments described above, the RF filter circuit and the LO filter circuit are configured as bandpass filters. However, it may be configured as a low-pass filter, a band rejection filter, or a high-pass filter.

  In the first and second embodiments described above, the direct conversion method is adopted for the receiving circuit. However, in addition to the direct conversion method, a double conversion method, a Low-IF method, or the like may be employed. According to these methods, the center frequency of the RF signal and the frequency of the LO signal are not the same, but any configuration may be used as long as the selection frequency of the RF filter circuit and the LO filter circuit is changed in the above embodiment. That is, circuit constants such as L and C may be changed in the RF filter and the LO filter. When the frequency setting circuit 105 or the amplitude setting circuit 207 generates a control signal to the RF filter circuit, the control signal is generated in consideration of the difference in circuit characteristics between the RF filter circuit and the LO filter circuit. As long as it is configured in advance.

  In the first and second embodiments described above, the frequency setting circuit 105 generates a control signal that decreases or increases the tuning frequency based on the phase shift indicated by the signal from the phase comparison circuit 104. is doing. Such a control signal may be generated such that the increase or decrease of the tuning frequency increases as the phase shift indicated by the signal from the phase comparison circuit 104 increases. Further, the frequency setting circuit 105 stores a change amount of the tuning frequency in association with the phase shift amount indicated by the signal from the phase comparison circuit 104, and the tuning frequency is changed based on the signal from the phase comparison circuit 104. A control signal that is only changed may be generated. Further, the control signal may be generated in the amplitude setting circuit 207 as described above.

  It should be noted that the frequency selectivity of the filter is improved at a desired channel frequency by mounting the receiving circuit of the present embodiment on a wireless communication device or a wired communication device. For example, when applied to a television receiver, a mobile phone, a wireless communication device, etc., the performance of these communication devices is improved.

It is a block diagram which shows the schematic structure of the receiver of 1st Embodiment which is one Embodiment of this invention. FIG. 2 is a circuit diagram illustrating a configuration of a receiving circuit included in the tuner unit of FIG. 1. FIG. 3 is a circuit diagram illustrating configurations of an RF filter circuit and an LO filter circuit of FIG. 2. It is a circuit diagram which shows the structure of the receiving circuit of 2nd Embodiment. FIG. 5 is a circuit diagram illustrating configurations of an RF filter circuit and an LO filter circuit of FIG. 4. FIG. 7 is a circuit diagram showing a configuration of a modification of the receiving circuit of FIG. 1. It is a circuit diagram which shows the structure of the receiving circuit of a prior art example.

Explanation of symbols

100 tuner unit 102 mixer circuit 104 phase comparison circuit 105 frequency setting circuit 106 input terminal 110 RF filter circuit 120 LO filter circuit 206 amplitude reference circuit 207 amplitude setting circuit 210 RF filter circuit 213 inductor 214 variable capacitor 215 variable resistor 220 LO filter circuit 700 Demodulator 800 Data processor 901 RF filter circuit 902 Mixer circuit 903 LO filter circuit 904 Variable voltage circuit 906 Controller

Claims (8)

An RF filter circuit that limits an RF (Radio Frequency) signal to a first frequency band based on a first tuning frequency;
A local oscillation filter circuit for limiting the local oscillation signal to the second frequency band based on the second tuning frequency;
First and second frequency changing means for changing the first and second tuning frequencies, respectively;
A mixer circuit that performs frequency conversion processing on a signal from the RF filter circuit based on a signal from the local oscillation filter circuit;
A signal indicating a phase difference between the local oscillation signal before the local oscillation filter circuit restricts to the second frequency band and the local oscillation signal after the local oscillation filter circuit restricts to the second frequency band. A phase comparator to generate;
Based on the signal generated by the phase comparison circuit, the first and second frequency bands are held at predetermined values in the RF filter circuit and the local oscillation filter circuit so that the center frequencies of the first and second frequency bands are held at predetermined values, respectively. And a control means for controlling the frequency changing means. An input unit to which an upper limit signal and a lower limit signal indicating upper and lower limits of the first and second tuning frequencies, respectively, are input;
The control means is
The receiving circuit according to claim 1, wherein the first and second frequency changing means are controlled based on the upper limit signal and the lower limit signal from the input unit. First and second amplitude changing means for changing the amplitudes of the output signals from the RF filter circuit and the local oscillation filter circuit, respectively;
An amplitude reference circuit for generating a signal indicating the amplitude of the local oscillation signal after the local oscillation filter circuit is limited to the second frequency band;
The control means is
Based on the signal generated by the amplitude reference circuit and the signal generated by the phase comparison circuit, the center frequencies of the first and second frequency bands are held at predetermined values in the RF filter circuit and the local oscillation filter circuit, respectively. And the first and second frequency changing means and the first and second amplitude changing means so that the amplitude of the RF signal and the output signal from the local oscillation filter circuit is held at a predetermined value. The receiving circuit according to claim 1, wherein the receiving circuit is controlled.   The receiving circuit according to claim 1, wherein each of the RF filter circuit and the local oscillation filter circuit is a band-pass filter circuit. The circuit configurations of the RF filter circuit and the local oscillation filter circuit are the same,
The control means is
The receiving circuit according to claim 1, wherein the same control signal is output to each of the first and second frequency changing means. A local oscillator for outputting a local oscillation signal to the local oscillation filter circuit;
6. The RF filter circuit, the local oscillation filter circuit, the phase comparator, the mixer circuit, and the local oscillation circuit are all constructed on the same substrate. Receiver circuit.   The receiving circuit according to claim 6, wherein both the RF filter circuit and the local oscillation filter circuit are configured by an LC filter including a negative resistance circuit.   A communication apparatus comprising the receiving circuit according to claim 1.

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