JP2014212360A - Automatic adjuster of tracking filter and receiver using the same - Google Patents

Abstract

The center frequency of a tracking filter is brought closer to a target frequency in a shorter time. A tracking filter automatic adjustment apparatus includes a capacitor circuit having a variable capacitance corresponding to a filter control signal, and a tracking filter for passing and outputting a component in a passband of a received signal; It has a level measuring unit 24 that measures and outputs the amplitude of the signal that has passed through the tracking filter 16, and a control unit 26 that generates a filter control signal. The control unit 26 generates, for each of a plurality of different target frequencies, a first signal level output from the level measurement unit 24 when generating a test signal having a first frequency lower than the target frequency by a predetermined frequency; Filter control is performed so that the difference from the second signal level output from the level measurement unit 24 is equal to or less than a predetermined threshold when a test signal having a second frequency higher than the target frequency by the predetermined frequency is generated. Generate signal and perform interpolation. [Selection] Figure 1

Description

  The present disclosure relates to tracking filter control, and more particularly to an automatic adjustment device for a tracking filter and a receiver using the same.

  The front end portion of the wireless communication receiver may have a tracking filter that can switch constants of resistors, capacitors, inductors, and other circuit elements by a control signal for the purpose of changing the center frequency in accordance with the reception frequency. Many. The tracking filter is used for the purpose of removing the influence of interference other than the desired wave by making the center frequency of the filter coincide with the target frequency that is the frequency of the desired signal to be received.

  When the center frequency of the tracking filter does not coincide with the target frequency, the interference wave of the nearby frequency is not sufficiently attenuated and is input to the next-stage amplifier. Usually, the receiver is equipped with an AGC (automatic gain control) system, and is controlled so that the input power to the next stage (the sum of the desired wave power and the interference wave power) is constant. For this reason, the smaller the attenuation of the interference wave, the greater the level of the interference wave input to the next stage and the lower the desired signal level. As a result, the SNR (signal-to-noise ratio) of the desired signal is reduced. Will fall.

  In general, variations in characteristics of circuit elements constituting an integrated circuit (IC) cannot be avoided. For this reason, in the case where all or part of the elements constituting the tracking filter are built in the IC, the differences in individual differences for each circuit, including variations in the values of the elements included in the tracking filter, are absorbed, It is required to automatically adjust the tracking filter corresponding to the received frequency.

  Usually, the tracking filter has a frequency characteristic that allows a signal in a relatively wide range of frequencies to pass therethrough. For this reason, the signal of the adjacent channel cannot be sufficiently attenuated, and the signal of the adjacent channel can be attenuated even in a subsequent filter or a digital filter to which a signal after AD (analog-to-digital) conversion is input. Many. In the vicinity of the center frequency of the tracking filter, the frequency characteristic of the tracking filter is relatively flat. Therefore, even if the value of the variable capacitor is changed, the level of the signal that has passed through the filter does not change much. For this reason, it is difficult to accurately match the center frequency of the tracking filter with the target frequency that is the frequency of the desired signal to be received.

  An example of a tracking filter adjustment method is described in Patent Document 1. In this method, test signals of two different frequencies p1 and p2 having the same level and the frequency equal to the lower side and the upper side and separated by α from the rated value f0 of the center frequency are sequentially supplied to the filter circuit unit. The levels V1 and V2 of the output signals sequentially output in response to the signals of are compared, and the constants of the filter circuit section having band pass (or band rejection) characteristics are switched in the control signal generation means according to the comparison result A control signal is generated and adjusted so that the difference value between levels V1 and V2 becomes zero.

JP 2008-98730 A

  However, in the tracking filter control method of Patent Document 1, it is necessary to input a test signal every time the reception frequency is switched, and to change the control signal to set the characteristics of the tracking filter. It takes time to get. In addition, test signals having two different frequencies separated from the target frequency by a frequency α with respect to a wide range of target frequencies are required, and in order to realize a test signal generation circuit capable of generating such a signal on an integrated circuit. The circuit scale becomes large. Further, this control method is based on the premise that the frequency characteristics on the minus side and the plus side are symmetric when viewed from the center frequency of the filter. In practice, it is difficult to construct a symmetric filter with respect to a wideband frequency.

  An object of the present invention is to make the center frequency of a tracking filter close to the target frequency in a shorter time with a relatively small circuit for a wide range of target frequencies.

  A tracking filter automatic adjustment device according to the present disclosure includes a test signal generation unit that generates a test signal having a frequency corresponding to a frequency control signal, and selects the test signal in an adjustment period, and selects a reception signal in other periods. And a switch circuit having a variable capacitor corresponding to the filter control signal, and a tracking filter that passes and outputs a component in the passband of the output of the switch, and passes through the tracking filter A level measurement unit that measures the amplitude of the received signal and outputs a measurement result; and a control unit that generates the filter control signal and the frequency control signal. The control unit causes the test signal generator to generate the test signal having a first frequency lower than the target frequency by a predetermined frequency for each of a plurality of different target frequencies. When the test signal generator generates the first signal level to be output as a measurement result and the test signal having a second frequency higher than the target frequency by the predetermined frequency, the level measurement unit performs the measurement result. The filter control signal is generated so that the difference from the second signal level output as a predetermined threshold or less is used, and the value of the filter control signal generated for each of the plurality of different target frequencies is used. By performing interpolation, a value corresponding to the new target frequency is obtained and used as the filter control signal for the new target frequency. Used.

  According to this, the filter control signal is generated so that the difference between the first signal level corresponding to the first frequency and the second signal level corresponding to the second frequency is equal to or less than the predetermined threshold. Since the first frequency and the second frequency are separated from the target frequency by the same frequency, the center frequency of the tracking filter can be made closer to the target frequency by the generated filter control signal.

  A receiver according to the present disclosure includes an automatic adjustment device for the tracking filter, performs a predetermined process on a signal that has passed through the automatic adjustment device for the tracking filter, and outputs the received signal. And a demodulator that outputs the obtained demodulated signal, a signal processor that performs predetermined signal processing on the demodulated signal and outputs the obtained signal, and a signal obtained by the signal processor An output unit that performs at least one of video display and audio output.

  According to this, since the center frequency of the tracking filter can be brought closer to the target frequency, the influence of the interference wave can be further reduced in the receiver.

  According to the present disclosure, the center frequency of the tracking filter can be made closer to the target frequency in a short time with a relatively small circuit for a wide range of target frequencies. Since the interference wave does not easily pass through the tracking filter, the influence of the interference wave can be further reduced in the receiver.

It is a block diagram which shows the structural example of the automatic adjustment apparatus of the tracking filter which concerns on embodiment of this invention. 6 is a graph showing an example of the relationship between the value of the filter control signal TC and the filter center frequency of the tracking filter 16. It is a graph which shows the example of the relationship between the value of the filter control signal TC about three frequencies, and the value of the filter center frequency obtained by curve interpolation using these values. It is a graph which shows the example of the relationship between the value of the filter control signal TC about three frequencies, and the value of the filter center frequency obtained by the linear interpolation using these values. It is a graph which shows the example of the relationship between the value of the filter control signal TC about more than 3 frequency, and the value of the filter center frequency obtained by curve interpolation using these values. It is a graph which shows the other example of curve interpolation. FIG. 7A is a graph showing an example of frequency characteristics of the tracking filter. FIG. 7B is a graph showing the difference obtained by subtracting the target frequency corresponding to the true center frequency of the tracking filter. FIG. 8A is a graph showing another example of frequency characteristics of the tracking filter. FIG. 8B shows a difference obtained by subtracting the value of the filter control signal that maximizes the transmittance of the tracking filter at the target frequency corresponding to the value of the obtained filter control signal. It is a graph. It is a block diagram which shows the other example of the automatic adjustment apparatus of the tracking filter of FIG. It is a block diagram which shows the other example of the automatic adjustment apparatus of the tracking filter of FIG. It is a graph which shows the example of the change according to the filter control signal of the frequency characteristic of a tracking filter. It is a block diagram which shows the other example of the automatic adjustment apparatus of the tracking filter of FIG. It is a block diagram which shows the structural example of the receiver which has the automatic adjustment apparatus of the tracking filter of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the components indicated by the same reference numerals in the last two digits correspond to each other and are the same or similar components.

  FIG. 1 is a block diagram showing a configuration example of an automatic adjustment device for a tracking filter according to an embodiment of the present invention. A tracking filter automatic adjustment apparatus 100 in FIG. 1 includes a low noise amplifier (LNA) 12, a switch 14, a tracking filter 16, an IF (intermediate frequency) amplifier 18, an AD (analog-to-digital) converter (ADC). ) 22, a level measurement unit 24, a control unit 26, and a test signal generation unit 30. The test signal generation unit 30 includes a reference signal generator 32 and a frequency dividing circuit 34.

  An antenna (not shown) receives the transmitted signal and supplies the received signal RS to the LNA 12. The LNA 12 amplifies the reception signal RS and outputs it. The switch 14 selects and outputs one of the output of the LNA 12 and the test signal TS output from the frequency divider circuit 34 in accordance with the switch control signal SC. The switch 14 selects the test signal TS during the adjustment period, and selects the output of the LNA 12 during other periods during which normal reception is performed. The tracking filter 16 passes and outputs the components in the pass band of the tracking filter 16 among the frequency components of the output of the switch 14. The passband and center frequency of the tracking filter 16 are determined based on the filter control signal TC.

  The control unit 26 controls the tracking filter 16 so that the center frequency of the tracking filter 16 becomes a target frequency that is a frequency (reception frequency) of a desired signal among the reception signals. The center frequency is a frequency at which attenuation by the tracking filter 16 is minimized. The pass band is a frequency range in which the difference between the attenuation by the tracking filter 16 and the attenuation at the center frequency is equal to or less than a predetermined value (for example, 0.5 dB).

  The IF amplifier 18 amplifies and outputs the output of the tracking filter 16. The ADC 22 converts the output of the IF amplifier 18 into a digital signal and outputs the digital signal. For example, in the receiver having the apparatus 100 of FIG. 1, subsequent processing such as frequency conversion and demodulation is performed on the output of the ADC 22. The level measuring unit 24 measures the amplitude of the output of the ADC 22 and outputs the measurement result as a received signal level. As the level measuring unit 24, a received signal strength indicator (RSSI) or an S meter may be used.

  The test signal generator 30 generates a test signal TS having a frequency corresponding to the frequency control signal RC. Specifically, the reference signal generator 32 generates and outputs a reference signal having a substantially constant frequency f0. The frequency dividing circuit 34 divides the reference signal output from the reference signal generator 32 by the frequency dividing ratio indicated by the frequency control signal RC, and outputs the frequency-divided signal to the switch 14 as the test signal TS. The control unit 26 generates and outputs a switch control signal SC, a filter control signal TC, and a frequency control signal RC based on the received signal level output from the level measuring unit 24.

  The tracking filter 16 is, for example, a tuned band-pass tracking filter including a capacitor circuit having a variable capacitance C (hereinafter referred to as C bank) and an inductor having a fixed inductance L. The C bank has N capacitors connected in parallel (N is a natural number) and N switches connected in series to the N capacitors. The filter control signal TC is an N-bit digital signal. The N bits of the filter control signal TC correspond to N switches, and the N switches are turned on or off based on the corresponding bits. Therefore, the variable capacitor C in the C bank of the tracking filter 16 has a value corresponding to the filter control signal TC.

The center frequency of the tracking filter 16 is the resonance frequency of the variable capacitor C and the fixed inductor L, and the following equation (1),
ωc = 1 / √ (L · C) (1)
It is represented by By changing the variable capacitance C of the tracking filter 16, the center frequency of the tracking filter 16 can be made substantially coincident with the target frequency.

  A specific procedure for the adjustment process of the tracking filter 16 that determines the value of the filter control signal TC will be described below. The control unit 26 sets the filter control signal TC to a predetermined initial value. The control unit 26 generates the switch control signal SC so that the switch 14 selects the test signal TS output from the frequency dividing circuit 34. Then, the switch 14 selects the test signal TS. A period during which the switch 14 selects the test signal TS is referred to as an adjustment period.

  The control unit 26 generates the frequency control signal RC so that the frequency of the test signal TS becomes a frequency (fc−Δf) lower than the target frequency fc by the frequency Δf. The control unit 26 stores the measurement result of the level measurement unit 24 at this time as the signal level S1.

  Next, the control unit 26 generates the frequency control signal RC so that the frequency of the test signal TS becomes a frequency (fc + Δf) higher than the target frequency fc by the frequency Δf. The control unit 26 stores the measurement result of the level measurement unit 24 at this time as the signal level S2.

  The control unit 26 compares the signal level S1 with the signal level S2. When the signal levels S1 and S2 are equal, the control unit 26 stores the value of the filter control signal TC at that time as an optimum value, and ends the adjustment process of the tracking filter 16. At this time, the control unit 26 generates the switch control signal SC so that the switch 14 selects the output of the LNA 12. The switch 14 selects the output of the LNA 12 and the adjustment period ends.

  If the signal levels S1 and S2 are not equal, the control unit 26 changes the filter control signal TC so that the frequency of the test signal TS becomes the frequency (fc−Δf). Do. When the filter control signal TC is changed, the tracking filter 16 changes the center frequency based on the filter control signal TC. When changing the filter control signal TC, the control unit 26 changes the value of the filter control signal TC so that the capacity of the C bank of the tracking filter 16 increases or decreases monotonously, for example. Thus, the control unit 26 generates the filter control signal TC so that the signal levels S1 and S2 are equal.

  Actually, the signal levels S1 and S2 may not be equal due to the influence of noise or the like. Therefore, the control unit 26 may generate the filter control signal TC so that the difference between the signal levels S1 and S2 is equal to or less than a predetermined threshold value. That is, when comparing the signal levels S1 and S2, the control unit 26 ends the adjustment process of the tracking filter 16 when the difference between the signal levels S1 and S2 is equal to or less than a predetermined threshold. Also good.

  As described above, according to the tracking filter automatic adjusting apparatus 100 of FIG. 1, the filter control signal TC is set to a value that equalizes the signal levels of fc + Δf and fc−Δf, that is, the target frequency fc with a relatively simple configuration. On the other hand, the optimum value of the filter control signal TC can be determined.

  The capacitance Ci of the i-th capacitor (i is a natural number where i ≦ N) included in the C bank of the tracking filter 16 may be set to Ci = C0 · 2 ^ (i−1) (C0 is a predetermined capacitance value, ^ Represents a power). If the i-th bit from the lowest order of the filter control signal TC controls the switch connected in series to the i-th capacitor, the capacity of the C bank is proportional to the value of the filter control signal TC.

  In this manner, since a wide range of capacitance values can be realized with a small number of elements, the number of capacitors occupying a large area on the integrated circuit can be reduced, and the circuit scale can be reduced. Furthermore, in this case, since a binary search for determining values in order from the most significant bit of the filter control signal TC can be performed, the time required to obtain the optimum value of the filter control signal TC can be shortened.

  FIG. 2 is a graph showing an example of the relationship between the value of the filter control signal TC and the filter center frequency of the tracking filter 16. Theoretically, if the optimal TC values at two certain frequencies are known, the TC values at other frequencies can be obtained by the equation (1). However, in the tracking filter 16 of FIG. 1, the filter center frequency and the passband frequency deviate from the design values, as shown in FIG. 2, due to variations in the quality of circuit elements and the influence of parasitic elements.

  FIG. 3 is a graph showing an example of the relationship between the value of the filter control signal TC for three frequencies and the value of the filter center frequency obtained by curve interpolation using these values. When changing the target frequency, the control unit 26 sets the value of the filter control signal TC corresponding to the new target frequency to two of the three target frequencies shown in FIG. 3 and the filter control corresponding to each of the three target frequencies. Using the signal value, the value is obtained by curve interpolation, and the obtained value is output to the tracking filter 16.

The simplest interpolation method is linear interpolation. FIG. 4 is a graph showing an example of the relationship between the value of the filter control signal TC for three frequencies and the value of the filter center frequency obtained by linear interpolation using these values. Actually, as shown in the above equation (1),
fc ∝ 1 / √C
Therefore, the interpolation using the curve as shown in FIG. 3 is more accurate than the linear interpolation as shown in FIG.

Therefore, when changing the target frequency, the control unit 26 sets the value of the filter control signal TC corresponding to the new target frequency f, for example,
TC = K1 * (C1-C2) / (f ^ 2) + C2 * K2-C1 * K3 (f ≧ f2) (2)
TC = K4 * (C2-C3) / (f ^ 2) + C3 * K5-C2 * K6 (f <f2) (3)
However, K1 to K6 may be obtained using an expression represented by a real constant, and the obtained value may be output to the tracking filter 16. The formula used is not limited to this, but a rational formula or the following polynomial (4), that is,
TC = a0 + a1.x + a2.x ^ 2 + a3.x ^ 3 + .. + am.x ^ m (4)
However, a0 to am may be a real constant, and m may be a natural number.

  FIG. 5 is a graph showing an example of the relationship between the value of the filter control signal TC for more than three frequencies and the value of the filter center frequency obtained by curve interpolation using these values. In the above, the example of obtaining the filter control signal TC for three frequencies and performing interpolation has been described, but as shown in FIG. 5, the values of the filter control signal TC for more than three frequencies are obtained, Interpolation may be performed. By obtaining the value of the filter control signal TC for a larger number of frequencies and performing interpolation, the accuracy of the value obtained by interpolation can be increased. As the frequency band covered by the tracking filter 16 becomes wider, the value of the filter control signal TC may be obtained for a larger number of frequencies.

  FIG. 6 is a graph showing another example of curve interpolation. The example in which the interpolation formula to be applied for each frequency section has been described above, but one interpolation formula may be used for all sections. That is, in FIG. 6, one interpolation formula passing through the point (f1, C1), the point (f2, C2),..., The point (fN, CN) is used. As the interpolation formula, for example, formula (4) is used. It is preferable to use a spline curve as the interpolation formula. This is because continuity can be ensured at the boundary of each section (such as the frequency f2 in FIG. 6).

  In the above example, it is assumed that the frequency characteristics of the tracking filter 16 are symmetric with respect to the center frequency of the tracking filter 16. However, in general, when the frequency range (band) covered by the tracking filter is wide, the center frequency moves while maintaining the shape of the graph indicating the filter characteristics when the filter adjustment signal TC is changed. It is difficult to design such a filter.

  FIG. 7A is a graph illustrating an example of frequency characteristics of the tracking filter 16. FIG. 7B is a graph showing a difference df obtained by subtracting a target frequency corresponding to the true center frequency of the tracking filter 16. When the target frequency fc is the frequencies f1, f2, and f3, the values of the generated filter control signal TC are C1, C2, and C3, respectively, and the true center frequencies of the filters are f1 ′, f2 ′, And f3 ′.

  As shown in FIG. 7A, as the variable width of the center frequency is larger, the shape of the filter becomes asymmetric as it approaches the end of the band. Thus, near the center of the band, the target frequency f2 corresponding to the filter control signal TC when (signal level S1) = (signal level S2) is a value close to the true center frequency f2 ′. On the other hand, the target frequency f1 ′ or the like does not necessarily coincide with the true center frequency f1 ′ or the like. The difference df obtained by subtracting the target frequency fc corresponding to the true center frequency of the filter changes monotonously with respect to the frequency f as shown in FIG.

  Therefore, the control unit 26 measures the differences df1, df2, and df3 in advance for the frequencies f1, f2, and f3, and holds the obtained differences. The relationship between the target frequency and the difference df (FIG. 7B) is relatively less affected by the variation among individuals, so there is little need to obtain the difference df for each chip. The control unit 26 generates the filter control signal TC for each of a plurality of different target frequencies f1, f2, and f3, and then sets the differences df1, df2, and df as offset values corresponding to the target frequencies f1, f2, and f3, respectively. Alternatively, interpolation is performed after adding df3.

  In other words, the control unit 26 corrects the values C1, C2, and C3 of the generated filter control signal TC by adding the difference df to each, that is, the true center frequencies f1 ′, f2 ′, And the various interpolation methods described above are applied, assuming that these are optimum values for f3 ′. That is, the control unit 26 is not the point (f1, C1), the point (f2, C2), and the point (f3, C3), but the point (f1 ′, C1), the point (f2 ′, C2), and the point ( Interpolation is performed by obtaining a curve passing through f3 ′, C3). As a result, the tracking filter 16 needs to cover a wide band, and even when the symmetry of the filter characteristics is broken depending on the frequency, the center frequency can be accurately matched with the target frequency.

  FIG. 8A is a graph showing another example of the frequency characteristic of the tracking filter 16. FIG. 8B is obtained by subtracting the value of the filter control signal TC that maximizes the transmittance of the tracking filter 16 at the target frequency corresponding to the obtained value of the filter control signal TC. It is a graph which shows difference dC. When the target frequency fc is the frequencies f1, f2, and f3, the values of the generated filter control signal TC are C1, C2, and C3, respectively, and the transmittance of the tracking filter 16 at the frequencies f1, f2, and f3. Suppose that the values of the filter control signal TC that maximize the value are C1 ′, C2 ′, and C3 ′, respectively.

  The difference dC changes monotonously with respect to the frequency f as shown in FIG. The control unit 26 sets C1 ′, C2 ′, and C3 ′ or differences dC1 = C1-C1 ′, dC2 = C2-C2 ′, and dC3 = C3-C3 ′ in advance for the frequencies f1, f2, and f3, respectively. Measure and keep the measurement results. The control unit 26 adds the difference dC1, dC2, or dC3 as an offset value corresponding to the filter control signal TC generated for each of the plurality of different target frequencies f1, f2, and f3, and then adds the difference dC1, dC2, or dC3 to the tracking filter 16. Output and perform interpolation.

  That is, the control unit 26 does not use the point (f1, C1), the point (f2, C2), and the point (f3, C3), but the point (f1, C1 ′), the point (f2, C2 ′), and the point ( A curve passing through f3, C3 ′) is obtained and interpolation is performed. The offset value dC corresponding to the target frequency f can be obtained by interpolation calculation according to the target frequency based on FIG. In this case, linear interpolation is sufficient in most cases. As a result, the tracking filter 16 needs to cover a wide band, and even when the symmetry of the filter characteristics is broken depending on the frequency, the center frequency can be accurately matched with the target frequency.

  FIG. 9 is a block diagram showing another example of the tracking filter automatic adjusting apparatus 100 of FIG. The tracking filter automatic adjustment apparatus 200 in FIG. 9 further includes an attenuator 211 between the antenna and the switch 14, and includes a control unit 226 instead of the control unit 26. It is constituted similarly.

  As described with reference to FIG. 1, the switch 14 selects the test signal TS during the adjustment period of the tracking filter 16. However, since the test signal TS is strong, it leaks to the LNA 12 and may be radiated as unnecessary radiation from the antenna. Therefore, the control unit 226 operates the attenuator 211 in the adjustment period in which the switch 14 selects the test signal TS, and attenuates the input signal. Since the signal input to the attenuator 211 is attenuated, leakage of the test signal TS to the antenna can be suppressed. As the attenuator 211, for example, an attenuator used as a part of an AGC (automatic gain control) circuit can be used.

  FIG. 10 is a block diagram showing another example of the tracking filter automatic adjustment apparatus 200 of FIG. The tracking filter automatic adjustment apparatus 300 in FIG. 10 further includes a variable gain amplifier 319 and is configured in the same manner as the apparatus 200 in FIG. 9 except that the control section 326 is provided instead of the control section 226.

  FIG. 11 is a graph showing an example of a change in the frequency characteristic of the tracking filter 16 according to the filter control signal TC. When the filter control signal TC is controlled to change the capacitance value of the tracking filter 16, the gain at the center frequency of the tracking filter 16 is not constant and has frequency characteristics (see FIG. 11). In particular, when the corresponding frequency covers a wide range, the gain difference is large even within the same band. Since the gain difference causes a difference in receiver sensitivity and SN (signal-to-noise) ratio, it is preferable that the gain difference be small.

  Therefore, in the apparatus 300 of FIG. 10, the variable gain amplifier 319 amplifies or attenuates the output of the IF amplifier 18 based on the gain control signal GC and outputs the amplified output to the ADC 22. The control unit 326 generates a gain control signal GC based on the target frequency and outputs the gain control signal GC to the variable gain amplifier 319 so that the fluctuation in the level of the signal input to the ADC 22 accompanying the change in the target frequency is reduced. Thereby, the change according to the frequency of the gain in the center frequency of the tracking filter 16 can be reduced.

  FIG. 12 is a block diagram illustrating another example of the tracking filter automatic adjustment apparatus 300 of FIG. The tracking filter automatic adjustment device 400 of FIG. 12 further includes a temperature detection unit 442 and is configured in the same manner as the device 300 of FIG. 10 except that a control unit 426 is provided instead of the control unit 326.

  So far, the case where the pass band of the tracking filter 16 is relatively broad has been described, but the pass band of the tracking filter 16 may be a narrow band. The characteristics of elements such as an inductor, a capacitor, and a resistor included in the filter change according to temperature. This change greatly affects the filter characteristics as the pass band of the filter is narrower.

  Therefore, in the apparatus 400 of FIG. 12, the temperature detection unit 442 detects the temperature of the tracking filter 16 or its surroundings, and notifies the control unit 426 of the detected temperature. The control unit 426 adjusts and outputs the value of the filter control signal TC based on the notified temperature so that the influence of the characteristic of the tracking filter 16 due to the temperature change is reduced. Thereby, the influence of the temperature change on the characteristics of the tracking filter 16 can be reduced.

  FIG. 13 is a block diagram showing a configuration example of a receiver having the tracking filter automatic adjustment apparatus 100 of FIG. 13 includes a receiving unit 82, a demodulating unit 84, a signal processing unit 86, and an audio / video output unit 88. The receiving unit 82 includes the tracking filter automatic adjusting device 100 of FIG. The receiving unit 82 may include the tracking filter automatic adjustment device 200, 300, or 400 shown in FIGS. 9, 10, and 12 instead of the device 100.

  As described with reference to FIG. 1, the apparatus 100 allows a component in the vicinity of a target frequency that is a frequency of a desired signal in the received signal RS to pass through and performs AD conversion. The receiving unit 82 performs processing such as frequency conversion on the AD-converted signal and outputs it. The demodulator 84 performs demodulation processing corresponding to the modulation scheme of the received signal RS on the output of the receiver 82 and outputs the obtained demodulated signal. The signal processor 86 performs predetermined signal processing such as decoding on the demodulated signal output from the demodulator 84, and outputs the obtained audio signal and / or video signal. The audio / video output unit 88 performs at least one of display of video represented by the video signal and output of audio represented by the audio signal.

  As described above, according to the present embodiment, the frequency of the required test signal does not need to correspond to every frequency in the band, and peripheral frequencies such as frequencies f1, f2, and f3 used for adjustment in advance are not required. It is sufficient that only a signal can be generated, and a test signal generator having a reference signal generator and a frequency dividing circuit that oscillates at a constant frequency can be used. Therefore, a PLL (phase locked loop) or the like is not required for the test signal generation unit, and the circuit scale can be reduced. Further, there is no need to input a test tone from the outside, and adjustment time can be shortened and simplified.

  Each functional block in this specification may typically be realized by hardware. For example, each functional block can be formed on a semiconductor substrate as part of an IC (integrated circuit). Here, the IC includes a large-scale integrated circuit (LSI), an application-specific integrated circuit (ASIC), a gate array, a field programmable gate array (FPGA), and the like. Alternatively, some or all of each functional block can be implemented in software. For example, such a functional block can be realized by a processor and a program executed on the processor. In other words, each functional block described in the present specification may be realized by hardware, may be realized by software, or may be realized by any combination of hardware and software.

  The many features and advantages of the present invention are apparent from the written description, and thus, it is intended by the appended claims to cover all such features and advantages of the invention. Further, since many changes and modifications will readily occur to those skilled in the art, the present invention should not be limited to the exact construction and operation as illustrated and described. Accordingly, all suitable modifications and equivalents are intended to be within the scope of the present invention.

  As described above, according to the present disclosure, it is possible to reduce the influence of an interference wave with a relatively simple circuit configuration. Therefore, the present invention provides an automatic adjustment device for a tracking filter and a reception using the same. This is useful for a vehicle-mounted radio tuner, for example.

12 Low noise amplifier 14 Switch 16 Tracking filter 18 IF amplifier 22 AD converter 24 Level measurement unit 26, 226, 326, 426 Control unit 30 Test signal generation unit 32 Reference signal generator 34 Divider circuit 80 Receiver 82 Receiver 84 Demodulation Unit 86 signal processing unit 88 audio / video output unit 100, 200, 300, 400 tracking filter automatic adjustment device 319 variable gain amplifier 442 temperature detection unit

Claims (9)

A test signal generator for generating a test signal having a frequency corresponding to the frequency control signal;
A switch that selects the test signal in the adjustment period, and selects and outputs the reception signal in the other period;
A tracking circuit having a capacitor circuit having a variable capacitance corresponding to a filter control signal, and outputting a component in a pass band among outputs of the switch;
A level measurement unit that measures the amplitude of the signal that has passed through the tracking filter and outputs a measurement result;
A control unit that generates the filter control signal and the frequency control signal;
The control unit causes the test signal generator to generate the test signal having a first frequency lower than the target frequency by a predetermined frequency for each of a plurality of different target frequencies. When the test signal generator generates the first signal level to be output as a measurement result and the test signal having a second frequency higher than the target frequency by the predetermined frequency, the level measurement unit performs the measurement result. The filter control signal is generated so that the difference from the second signal level output as a predetermined threshold or less is used, and the value of the filter control signal generated for each of the plurality of different target frequencies is used. By performing interpolation, a value corresponding to the new target frequency is obtained and used as the filter control signal for the new target frequency. Automatic adjusting apparatus of the tracking filter used. In the automatic adjustment device of the tracking filter according to claim 1,
The test signal generator is
A reference signal generator for generating a reference signal of a predetermined frequency;
A tracking filter automatic adjustment device comprising: a frequency divider that divides the reference signal and outputs the frequency as the test signal. In the automatic adjustment device of the tracking filter according to claim 1 or 2,
The capacitor circuit includes N capacitors (N is an integer of 2 or more) that can be connected in parallel, and the capacitance Ci of the i-th capacitor among the N capacitors is (i is a natural number where i ≦ N). ), Ci = C0 · 2 ^ i (C0 is a predetermined capacitance value, and ^ represents a power). In the automatic adjustment apparatus of the tracking filter of any one of Claims 1-3,
An attenuator is further provided between the antenna that supplies the received signal and the switch,
The attenuator is an automatic adjustment device for a tracking filter that attenuates an input signal during the adjustment period. In the automatic adjustment apparatus of the tracking filter of any one of Claims 1-4,
A temperature detection unit for detecting the temperature;
The control unit is an automatic adjustment device for a tracking filter that adjusts a value of the filter control signal based on a detected temperature so that an influence of a temperature change in characteristics of the tracking filter is reduced. In the automatic adjustment apparatus of the tracking filter of any one of Claims 1-5,
An automatic adjustment device for a tracking filter that performs interpolation after adding an offset value corresponding to each of the plurality of different target frequencies after generating the filter control signal for each of the plurality of different target frequencies . In the automatic adjustment apparatus of the tracking filter of any one of Claims 1-5,
The tracking filter automatic adjustment device that performs interpolation after adding an offset value to the value of the filter control signal generated for each of the plurality of different target frequencies. In the automatic adjustment apparatus of the tracking filter of any one of Claims 1-5,
A variable gain amplifier that amplifies the signal that has passed through the tracking filter with a gain according to a gain control signal;
The control unit is an automatic adjustment device for a tracking filter that generates the gain control signal. A receiver that has the tracking filter automatic adjustment device according to any one of claims 1 to 5, performs a predetermined process on a signal that has passed through the tracking filter automatic adjustment device, and outputs the received signal,
A demodulator that performs demodulation processing on the output of the receiver and outputs the obtained demodulated signal;
A signal processing unit that performs predetermined signal processing on the demodulated signal and outputs the obtained signal;
A receiver comprising: an output unit that performs at least one of video display and audio output represented by the signal obtained by the signal processing unit.

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