WO2016136040A1

WO2016136040A1 - Fm reception device and fm reception method

Info

Publication number: WO2016136040A1
Application number: PCT/JP2015/081367
Authority: WO
Inventors: 奥畑　康秀
Original assignee: 株式会社Ｊｖｃケンウッド
Priority date: 2015-02-23
Filing date: 2015-11-06
Publication date: 2016-09-01
Also published as: JP2016157995A; JP6264308B2

Abstract

According to the present invention, a quadrature detection unit 12 performs quadrature detection on an FM signal by means of a local oscillation signal output from a local oscillator 28, and outputs a baseband signal. A first reduction unit 30 and second reduction unit 32 reduce a DC component included in the baseband signal. A correction unit 34 reproduces the DC component by correcting the baseband signal so as to be centered on the origin of the polar coordinates on an IQ plane. An FM detection unit 24 performs FM detection on the corrected baseband signal and generates a detection signal. An addition unit 62 smooths the detection signal and adds an offset. An AFC unit 66 generates a control signal for controlling the frequency of the local oscillation signal on the basis of the detection signal which has been smoothed and to which an offset has been added, and feeds the control signal back to the local oscillator 28.

Description

FM receiver and FM receiving method

The present invention relates to a receiving technique, and more particularly to an FM receiving apparatus and an FM receiving method for receiving an FM signal.

A direct conversion FM (Frequency Modulation) receiver converts an RF signal into a baseband signal by quadrature detection, and then amplifies the baseband signal with an amplifier. Since an unnecessary DC component is output by the amplifier, the FM receiver reduces the DC component included in the baseband signal by the coupling capacitor. Further, the FM receiver FM-detects a baseband signal with a reduced DC component (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 3-16349

When the direct conversion type FM receiver includes a coupling capacitor, not only unnecessary DC components by the amplifier are reduced, but also DC components and low frequency components of the baseband signal may be reduced. Such a reduction causes distortion components after FM detection. Also, when an unmodulated signal is received and the frequency of the received signal is the same as the frequency of the local oscillation signal, the baseband signal is only a direct current component, and thus all signals are cut by the coupling capacitor. . As a result, only the noise received by the antenna and the noise generated inside are subjected to FM detection, so that the signal after FM detection becomes only noise.

The present invention has been made in view of such a situation, and an object thereof is to provide a technique for improving the quality of an FM detected signal.

In order to solve the above-described problem, an FM receiver according to an aspect of the present embodiment includes a local oscillator that outputs a local oscillation signal, and a baseband by orthogonally detecting the FM signal using the local oscillation signal output from the local oscillator. A quadrature detector that outputs a signal, a reduction unit that reduces a DC component included in the baseband signal output from the quadrature detector, and a baseband signal that is centered on the origin of polar coordinates on the IQ plane. A correction unit that reproduces a DC component by correction, an FM detection of a baseband signal corrected by the correction unit to generate a detection signal, and a detection signal generated by the FM detection unit are smoothed and an offset is set. Adder to be added, and control to control the frequency of the local oscillation signal based on the smoothed and offset detection signal No. generates, and a AFC unit for feeding back the control signal to the local oscillator.

Another aspect of this embodiment is an FM reception method. This method includes a step of performing quadrature detection of an FM signal using a local oscillation signal output from a local oscillator, outputting a baseband signal, a step of reducing a direct current component included in the baseband signal, and a baseband signal. Are corrected so that the origin of the polar coordinates is centered on the IQ plane, a step of reproducing the DC component, a step of generating a detection signal by FM detection of the corrected baseband signal, and a step of generating the detected signal Smoothing and adding an offset; generating a control signal for controlling the frequency of the local oscillation signal based on the smoothed offset-added detection signal; and feeding back the control signal to the local oscillator; Is provided.

It should be noted that any combination of the above-described constituent elements and a representation of the present embodiment converted between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present embodiment.

According to the present embodiment, the quality of the FM detected signal can be improved.

1 is a diagram illustrating a configuration of a receiving apparatus according to Embodiment 1. FIG. It is a figure which shows the structure of the DC correction value detection part of FIG. It is a figure which shows the several area | region prescribed | regulated in the phase determination part of FIG. It is a figure which shows the transmission spectrum of the transmission signal with respect to the receiver of FIG. It is a figure which shows the quadrature detection spectrum of the baseband signal output from the 1st reduction part of FIG. 1, and a 2nd reduction part. It is a figure which shows the I and Q pattern of the transmission signal in FIG. 4, FIG. 5, and a baseband signal. It is a figure which shows the waveform of the transmission signal in FIG. 4, FIG. 5, and a detection signal. FIG. 6 is a diagram illustrating a configuration of a receiving apparatus according to a second embodiment. FIG. 10 is a diagram illustrating a configuration of a receiving apparatus according to a third embodiment. 10 is a flowchart showing a control procedure by the receiving device of FIG. 9.

(Example 1)
Before describing the present invention specifically, an outline will be given first. The first embodiment relates to a direct conversion type FM receiver mainly composed of a quadrature detector and an FM detector. By arranging a coupling capacitor between the quadrature detector and the FM detector, it is not necessary to perform correction even if there is a deviation of the origin of the orthogonal coordinates between the quadrature detector and the FM detector. However, when the unmodulated signal is received, if the frequency shift between the received signal and the local oscillation signal is converged to zero by AFC, the output of the quadrature detector stops at one point on the circle of the IQ plane coordinates, The level of the signal input to the FM detector is attenuated by the coupling capacitor so as to approach the origin. Arctan detection in the FM detector outputs the amount of change in phase rotation, so if the input is concentrated near the origin, phase rotation due to irregular noise will be detected. As a result, the result of FM detection becomes noise. On the other hand, when the received signal is unmodulated, the FM detection result should be silent. To cope with this, the AFC is performed so that the rotation of the quadrature detection output does not stop on the IQ plane coordinates, that is, the frequency of the reception signal and the frequency of the local oscillation signal are kept constant. Instead of setting the convergence target of the frequency shift to zero, it converges to the offset value.

However, when the received signal is modulated and the DC component is included in the orthogonally detected baseband signal, the DC component is also suppressed, and the FM detection signal is distorted. In order to cope with this, in the FM receiver according to the present embodiment, the baseband signal is converted into an amplitude signal and a phase signal, and then the deviation of the baseband signal from the origin is detected. Further, the baseband signal is corrected using this shift as a correction value. That is, since the constellation is a circle, the above processing corrects the center of the circle to be the origin of the I and Q planes. Thereby, the DC component on the spectrum of the baseband band is equivalently reproduced, and the distortion of the FM detection signal is suppressed.

FIG. 1 illustrates a configuration of a receiving device 100 according to the first embodiment. The receiving apparatus 100 includes an antenna 10, a quadrature detection unit 12, a first reduction unit 30, a second reduction unit 32, a first ADC unit 14, a second ADC unit 16, a correction unit 34, an FM detection unit 24, an averaging unit 60, and an addition Section 62, offset storage section 64, AFC section 66, DAC section 68, and local oscillator 28. The quadrature detection unit 12 includes a first amplification unit 40, a distribution unit 42, a phase shift unit 44, a first mixer 46, a first LPF unit 48, a second amplification unit 50, a second mixer 52, a second LPF unit 54, and a third amplification. The correction unit 34 includes a first correction unit 18, a second correction unit 20, and a DC correction value detection unit 22, and the AFC unit 66 includes a third LPF unit 70 and a fourth amplification unit 72.

The antenna 10 receives an RF (Radio Frequency) signal from a transmission device (not shown). The antenna 10 outputs the received RF signal (hereinafter also referred to as “received signal”) to the first amplifying unit 40. The first amplifying unit 40 is an LNA (Low Noise Amplifier) and amplifies the RF signal from the antenna 10. The first amplification unit 40 outputs the amplified RF signal to the distribution unit 42. The distribution unit 42 separates the RF signal from the first amplification unit 40 into two systems. The distributor 42 outputs the separated RF signal to the first mixer 46 and the second mixer 52.

The local oscillator 28 adjusts the frequency of the local oscillation signal according to the control signal from the DAC unit 68, and outputs the local oscillation signal whose frequency is adjusted to the phase shift unit 44 and the first mixer 46. Here, the local oscillator 28 increases the frequency of the local oscillation signal as the voltage of the control signal increases. The phase shifter 44 shifts the local oscillation signal from the local oscillator 28 by 90 degrees. The phase shifter 44 outputs the phase-shifted local oscillation signal to the second mixer 52.

The first mixer 46 multiplies the RF signal from the distributor 42 and the local oscillation signal from the local oscillator 28 to generate an I-phase baseband signal (hereinafter referred to as “I signal”). The first mixer 46 outputs the I signal to the first LPF unit 48. The second mixer 52 multiplies the RF signal from the distribution unit 42 and the local oscillation signal from the phase shift unit 44 to generate a Q-phase baseband signal (hereinafter referred to as “Q signal”). The second mixer 52 outputs the Q signal to the second LPF unit 54.

The first LPF unit 48 performs band limitation by removing a signal having a frequency equal to or higher than the cutoff frequency from the I signal from the first mixer 46. The first LPF unit 48 outputs a low-frequency component I signal (hereinafter also referred to as “I signal”) to the second amplifying unit 50. The second LPF unit 54 performs band limitation by removing a signal having a frequency equal to or higher than the cutoff frequency from the Q signal from the second mixer 52. The second LPF unit 54 outputs a low-frequency component Q signal (hereinafter also referred to as “Q signal”) to the third amplifying unit 56.

The second amplification unit 50 amplifies the I signal from the first LPF unit 48, and the third amplification unit 56 amplifies the Q signal from the second LPF unit 54. As described above, the quadrature detection unit 12 performs quadrature detection of the RF signal. The quadrature detection unit 12 is composed of an analog device, for example, one chip. In analog devices, the I signal output from the second amplifying unit 50 and the Q signal output from the third amplifying unit 56 may include unnecessary DC components due to the configuration. As a result, a DC offset voltage is added to these signals.

The first reduction unit 30 inputs the I signal from the second amplification unit 50. The first reduction unit 30 is configured by, for example, a coupling capacitor, and reduces the direct current component included in the I signal. The first reduction unit 30 outputs an I signal (hereinafter also referred to as “I signal”) having a reduced DC component to the first ADC unit 14. The second reduction unit 32 receives the Q signal from the third amplification unit 56. Similarly to the first reduction unit 30, the second reduction unit 32 is configured with a coupling capacitor, and reduces the direct current component included in the Q signal. The second reduction unit 32 outputs a Q signal (hereinafter also referred to as “Q signal”) having a reduced direct current component to the second ADC unit 16. Due to the first reduction unit 30 and the second reduction unit 32, the DC offset voltage of the baseband signal output from the quadrature detection unit 12 does not affect thereafter.

The first ADC unit 14 performs analog / digital conversion on the I signal from the first reduction unit 30. The first ADC unit 14 outputs an I signal (hereinafter also referred to as “I signal”) converted into a digital signal to the first correction unit 18. The second ADC unit 16 performs analog / digital conversion on the Q signal from the second reduction unit 32. The second ADC unit 16 outputs a Q signal converted to a digital signal (hereinafter also referred to as “Q signal”) to the second correction unit 20.

As described above, the correction unit 34 includes the first correction unit 18, the second correction unit 20, and the DC correction value detection unit 22. The DC correction value detection unit 22 detects a deviation from the origin of the constellation on the IQ plane. The first correction unit 18 and the second correction unit 20 correct the deviation from the origin of the constellation on the IQ plane.

The first correction unit 18 receives the I signal output from the first ADC unit 14 and also receives the I-phase correction value 200 from the DC correction value detection unit 22. The first correction unit 18 adds the I signal and the I-phase correction value 200 to perform correction using the I-phase correction value 200 on the I signal. The first correction unit 18 outputs the corrected I signal as the I signal 204 to the DC correction value detection unit 22 and the FM detection unit 24.

The second correction unit 20 receives the Q signal output from the second ADC unit 16 and also receives the Q-phase correction value 202 from the DC correction value detection unit 22. The second correction unit 20 adds the Q signal and the Q-phase correction value 202 to perform correction using the Q-phase correction value 202 on the Q signal. The second correction unit 20 outputs the corrected Q signal as the Q signal 206 to the DC correction value detection unit 22 and the FM detection unit 24.

The DC correction value detection unit 22 receives the I signal 204 from the first correction unit 18 and the Q signal 206 from the second correction unit 20, and based on them, the I phase correction value 200 and the Q phase correction value. 202 is generated. The I-phase correction value 200 and the Q-phase correction value 202 will be described later. The DC correction value detection unit 22 outputs the I-phase correction value 200 to the first correction unit 18 and outputs the Q-phase correction value 202 to the second correction unit 20. Here, the configuration of the DC correction value detection unit 22 will be described with reference to FIG.

FIG. 2 shows the configuration of the DC correction value detection unit 22. The DC correction value detection unit 22 includes a first squaring unit 110, a second squaring unit 112, a phase determination unit 114, a first addition unit 116, a DEMUX 118, a first averaging unit 120, a second averaging unit 122, 3 average part 124, 4th average part 126, 2nd addition part 128, and 3rd addition part 130 are included.

The first squaring unit 110 receives the I signal 204 and derives the square value thereof. The first squaring unit 110 outputs the square value of the I signal 204 to the phase determination unit 114 and the first addition unit 116. The second squaring unit 112 receives the Q signal 206 and derives the square value thereof. The second squaring unit 112 outputs the square value of the Q signal 206 to the phase determination unit 114 and the first addition unit 116.

The first addition unit 116 inputs the square value of the I signal 204 from the first squaring unit 110 and the square value of the Q signal 206 from the second squaring unit 112. The first adder 116 adds the square value of the I signal 204 and the square value of the Q signal 206. The result of the addition is the power value P of the I signal 204 and the Q signal 206. The power value P is a square value of the amplitude signal when the I signal 204 and the Q signal 206 are converted into polar coordinates. Therefore, the processing by the first squaring unit 110, the second squaring unit 112, and the first adding unit 116 corresponds to a process for deriving an amplitude signal. The first addition unit 116 outputs the power value P to the DEMUX 118.

The phase determination unit 114 receives the I signal 204 and the Q signal 206 and also receives the square value of the I signal 204 from the first squaring unit 110 and the square value of the Q signal 206 from the second squaring unit 112. Enter. Based on these values, the phase determination unit 114 identifies the phase region. To explain this, FIG. 3 is used. FIG. 3 shows a plurality of regions defined in the phase determination unit 114. This is the IQ plane, the horizontal axis corresponds to the I axis, and the vertical axis corresponds to the Q axis. As shown, the four phase regions A1 to A4 are defined so as not to overlap each other. Here, the phase region A1 is in the range of π / 2 from 7π / 4 to π / 4, the phase region A2 is in the range of π / 2 from π / 4 to 3π / 4, and the phase region A3 Is a range of π / 2 from 3π / 4 to 5π / 4, and the phase region A4 is a range of π / 2 from 5π / 4 to 7π / 4.

In the following, for the sake of clarity, the I signal 204 is indicated as “I”, the Q signal 206 is indicated as “Q”, the square value of the I signal 204 is indicated as “I ² ”, and the square of the Q signal 206 is indicated. The value is indicated as “Q ² ”. The phase determination unit 114 performs classification into four phase regions A1, A2, A3, and A4 based on the following determination conditions.
A1: I ² ≧ Q ² , I ≧ 0
A2: I ² <Q ² , Q ≧ 0
A3: I ² ≧ Q ² , I <0
A4: I ² <Q ² , Q <0
The phase determination unit 114 outputs the identified phase region as the phase region signal 208. When the identified phase region changes with time, for example, A1, A2, A3, A4, A1, A2,... Sequentially, the phase region signal 208 is also A1, A2, A3, A4, A1,. A2 changes sequentially. Such processing by the phase determination unit 114 corresponds to processing for deriving a phase signal when the I signal 204 and the Q signal 206 are subjected to polar coordinate conversion. Returning to FIG.

The DEMUX 118 sequentially inputs the power value P from the first addition unit 116 and the phase region signal 208 of the phase determination unit 114. The power value P and the phase region signal 208 are synchronized. The DEMUX 118 outputs the power value P as one of the power values P1 to P4 according to the phase region indicated by the phase region signal 208. More specifically, the DEMUX 118 outputs a power value P1 if it is the phase region A1, outputs a power value P2 if it is the phase region A2, and outputs a power value P3 if it is the phase region A3. If it is A4, the power value P3 is output. That is, the DEMUX 118 is a distributor (Demultiplexer) that distributes the power value P from the power values P1 to P4 in accordance with the phase region indicated by the phase region signal 208.

The first averaging unit 120 calculates the average power P1 for a certain period of the input power value P1, and outputs the average power P1 to the second addition unit 128. For the average, for example, a moving average is used. The second averaging unit 122 calculates the average power P2 for a certain period of the input power value P2, and outputs the average power P2 to the third addition unit 130. The third averaging unit 124 calculates the average power P3 for a certain period of the input power value P3 and outputs the average power P3 to the second addition unit 128. The fourth averaging unit 126 calculates the average power P4 for a certain period of the input power value P4 and outputs the average power P4 to the third addition unit 130. The processing from the first averaging unit 120 to the fourth averaging unit 126 corresponds to deriving the average value of the amplitude signal for each phase region.

The second adding unit 128 receives the average power P1 from the first averaging unit 120 and the average power P3 from the third averaging unit 124. The second addition unit 128 subtracts the average power P1 from the average power P3. The second addition unit 128 outputs the subtraction result as the I-phase correction value 200. The third adding unit 130 receives the average power P2 from the second averaging unit 122 and the average power P4 from the fourth averaging unit 126. The third addition unit 130 subtracts the average power P2 from the average power P4. The third addition unit 130 outputs the subtraction result as the Q phase correction value 202. As described above, the DC correction value detection unit 22 obtains a deviation from the origin of the I signal 204 and the Q signal 206 based on the power value for each phase region, that is, the average value of the value corresponding to the amplitude signal. Are output as an I-phase correction value 200 and a Q-phase correction value 202. This is because the I-phase correction value 200 and the Q-phase correction value 202 are derived so that the amplitude in each of a plurality of phase regions defined on the IQ plane is close, that is, the I and Q of the baseband signal on the IQ plane. This corresponds to deriving a correction value for correcting the position of the pattern so as to be a circle centered on the origin of polar coordinates.

The input of the DC correction value detection unit 22 is the output from the first correction unit 18 and the second correction unit 20, but is not limited thereto, and is extracted from the input side of the first correction unit 18 and the second correction unit 20. The correction may be performed by the first correction unit 18 and the second correction unit 20, and the I signal 204 and the Q signal 206 may be output.

The correction unit 34 is a polar coordinate origin correction unit on the IQ plane, but is not limited to the above-described embodiment. For example, if the constellation is deviated from the origin, there will be an amplitude component. Therefore, from the I-axis and Q-axis components of the maximum and minimum vectors of the vector from the origin to one point on the constellation. A baseband signal may be corrected by deriving a correction value. Returning to FIG.

The FM detection unit 24 performs FM detection on the corrected baseband signal. As the FM detection, for example, Arctan detection is executed. In Arctan detection, each of the I signal 204 and the Q signal 206 is defined as two sides of a triangle, and angles thereof are derived. Since the change in the angle per unit time becomes the angular velocity, that is, the frequency, the FM modulation can be demodulated. The FM detection unit 24 outputs a detection signal that is a result of the FM detection. The output detection signal is, for example, an audio signal. Of course, not only audio signals but also all modulation schemes that can be detected by FM detectors can be handled.

The averaging unit 60 inputs the detection signal from the FM detection unit 24. The averaging unit 60 outputs the average voltage to the adding unit 62 by averaging the detection signal over a certain period. For the average, for example, a moving average is used. The average voltage is proportional to the frequency of the difference between the center frequency of the received signal and the output frequency of the local oscillation signal. Therefore, for example, if the average voltage is “0”, these frequencies match. As described above, when an unmodulated signal is received, if the frequency shift between the received signal and the local oscillation signal is converged to zero by AFC, the I signal and the Q signal stop at one point on the coordinate circle, and FM The level of the signal input to the detector 24 is attenuated so as to approach the origin. In order to cope with this, the following processing is executed.

The offset storage unit 64 stores a predetermined offset value. The adding unit 62 receives the offset value from the offset storage unit 64 and the average voltage from the averaging unit 60. The adding unit 62 adds an offset value to the average voltage and outputs the result to the third LPF unit 70. When there is no addition of the offset value in the adding unit 62, the AFC unit 66 controls the center frequency of the received signal and the frequency of the local oscillation signal to be the same, but the adding unit 62 adds a certain offset value. The local oscillation signal has a frequency offset corresponding to the offset value. If this frequency offset is set to a frequency that is not reduced by the first reduction unit 30 and the second reduction unit 32, the I signal and the Q signal do not become DC components even when the RF signal is unmodulated. The frequency is the same as the frequency offset. Therefore, even when an unmodulated RF signal is input, the detection signal does not become noise.

The third LPF unit 70 inputs an average voltage (hereinafter also referred to as “average voltage”) to which the offset value is added from the addition unit 62. The third LPF unit 70 performs low-pass processing on the average voltage. The third LPF unit 70 outputs the average voltage (hereinafter also referred to as “average voltage”) subjected to the low-pass processing to the fourth amplifying unit 72. The fourth amplifying unit 72 generates a control signal by amplifying the average voltage from the third LPF unit 70. The gain of the AFC loop is determined by the amplification in the fourth amplification unit 72.

The DAC unit 68 performs digital / analog conversion on the control signal from the fourth amplification unit 72 and outputs an analog signal control signal (hereinafter also referred to as “control signal”) to the local oscillator 28. As described above, the AFC unit 66 generates a control signal for controlling the frequency of the local oscillation signal based on the average voltage added with the offset in the adding unit 62, and feeds back the control signal to the local oscillator 28. The addition of the offset corresponds to controlling the frequency of the local oscillation signal output from the local oscillator 28 so that the phase component subjected to polar coordinate conversion in the DC correction value detection unit 22 rotates.

AFC control is not limited to the above-described embodiment. If the frequency of the local oscillator 28 is set by a fractional PLL, AFC control is also possible by setting the frequency division ratio. In this case, conversion to an analog voltage by the DAC unit 68 is not necessary.

In this way, even when there is a certain offset between the frequency of the received signal and the frequency of the local oscillation signal, the DC component of the baseband signal output from the quadrature detection unit 12 is the first reduction unit 30 and the second The detection unit 32 is suppressed by the reduction unit 32, and the detection signal is distorted.

FIG. 4 shows the transmission spectrum converted into the baseband band of the transmission signal for the receiving apparatus 100. The horizontal axis represents frequency and the vertical axis represents power. This shows the transmission spectrum of an FM modulated signal with a modulated signal of 1 kHz and a deviation of 1.5 kHz. As shown in the figure, the line spectrum is 1 kHz apart and symmetrical from the center frequency.

Here, it is assumed that the offset value output from the offset storage unit 64 corresponds to an offset frequency of 1 kHz. In this case, the baseband signals output from the first reduction unit 30 and the second reduction unit 32 are as shown in FIG. FIG. 5 shows the quadrature detection spectrum of the baseband signal output from the first reduction unit 30 and the second reduction unit 32. The horizontal axis represents frequency and the vertical axis represents power. As shown in the figure, there is a frequency offset of 1 kHz, and the signal component frequency-converted to DC is suppressed. This is shown in FIG. 6 in the IQ plane. FIG. 6 shows I and Q patterns of the transmission signal and the baseband signal. The horizontal axis indicates the I axis, and the vertical axis indicates the Q axis. The I and Q patterns of the transmission signal to be compared are indicated by dotted lines and are circles centered on the origin. On the other hand, since the DC component is suppressed in the baseband signal, the I and Q patterns of the baseband signal are circles whose center points are deviated from the origin as indicated by the solid line.

A detection signal obtained by detecting such a baseband signal by the FM detection unit 24 is shown in FIG. FIG. 7 shows the modulation waveform of the transmission signal and the demodulation waveform of the detection signal. The horizontal axis indicates time, and the vertical axis indicates amplitude. The modulation waveform of the transmission signal to be compared is indicated by a dotted line and has a sin wave shape. On the other hand, the detection signal is indicated by a solid line, and a distortion component is generated due to suppression of the DC component.

The DC correction value detection unit 22 derives a correction value for correcting the position of the I and Q pattern of the baseband signal on the IQ plane into a circle whose center is the polar coordinate origin. The DC correction value detection unit 22 generates an I-phase correction value 200 and a Q-phase correction value 202 for correcting the center of the I and Q pattern circles of the baseband signal in FIG. In addition, since the first correction unit 18 performs correction using the I-phase correction value 200 and the second correction unit 20 performs correction using the Q-phase correction value 202, distortion of the detection signal is suppressed. That is, the first correction unit 18 and the second correction unit 20 are equivalently restoring the suppressed DC component of the baseband signal.

This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it can be realized by a program loaded in the memory, but here it is realized by their cooperation. Draw functional blocks. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

For example, the first reduction unit 30 and the second reduction unit 32 are configured by coupling capacitors. However, the first ADC unit 14 and the second ADC unit 16 digitize the I signal and the Q signal, and then perform digital processing. It may be realized by HPF (High Pass Filter).

According to this embodiment, since a certain offset is added between the frequency of the received signal and the frequency of the local transmission signal, it is possible to suppress the possibility that the baseband signal is completely cut even when an unmodulated signal is input. . In addition, since the possibility that the baseband signal is completely cut is suppressed, it is possible to avoid the FM detection output from being only noise as in the case where the RF signal is not received. Further, since it is avoided that the FM detection output is only noise, the quality of the FM detected signal can be improved. Further, in the IQ plane, when the center is shifted from the origin by the I signal and Q signal whose DC components are reduced, this is corrected, so that the missing DC component on the baseband band spectrum can be reproduced. In addition, since the missing DC component is reproduced, distortion of the detection signal can be suppressed.

(Example 2)
Next, Example 2 will be described. As in the first embodiment, the second embodiment relates to an FM receiver that is a direct conversion type and has a coupling capacitor disposed between a quadrature detector and an FM detector. In the first embodiment, in order to make the frequency of the reception signal and the frequency of the local oscillation signal not coincide with each other, the AFC is executed after adding the offset value to the detection signal. On the other hand, in the second embodiment, in order not to make the frequency of the received signal coincide with the frequency of the local oscillation signal, the control signal to be input to the local oscillator is FM-modulated without using AFC. As a result, the frequency of the local oscillation signal varies in accordance with the FM modulation.

FIG. 8 illustrates a configuration of the receiving device 100 according to the second embodiment. The receiving apparatus 100 includes an antenna 10, a quadrature detection unit 12, a first reduction unit 30, a second reduction unit 32, a first ADC unit 14, a second ADC unit 16, a correction unit 34, an FM detection unit 24, a first local oscillator 90, A second local oscillator 92 is included. The quadrature detection unit 12 includes a first amplification unit 40, a distribution unit 42, a phase shift unit 44, a first mixer 46, a first LPF unit 48, a second amplification unit 50, a second mixer 52, a second LPF unit 54, and a third amplification. The correction unit 34 includes a first correction unit 18, a second correction unit 20, and a DC correction value detection unit 22. Here, it demonstrates centering on the difference from before.

The first local oscillator 90 outputs the first local oscillation signal to the second local oscillator 92. The second local oscillator 92 adjusts the frequency of the second local oscillation signal in accordance with the first local oscillation signal from the first local oscillator 90, and the second local oscillation signal whose frequency is adjusted is transferred to the first mixer 46. It outputs to the phase part 44. This corresponds to outputting the second local oscillation signal frequency-modulated by the first local oscillation signal from the first local oscillator 90 to the quadrature detection unit 12. The first mixer 46 and the second mixer 52 of the quadrature detection unit 12 perform quadrature detection of the FM signal from the distribution unit 42 using the second local oscillation signal output from the second local oscillator 92 and output a baseband signal. To do. That is, the second local oscillation signal corresponds to the local oscillation signal in the first embodiment.

Thus, the baseband signal is generated by quadrature detection of the RF signal using the second local oscillation signal that is FM-modulated by the first local oscillation signal. Therefore, even when the received signal is unmodulated and the frequency of the received signal matches the frequency of the second local oscillation signal, the baseband signal does not become a constant value, so that it is prevented from being completely suppressed. . Even when the baseband signal includes a DC component as in the first embodiment, the correction unit 34 corrects the DC component. In addition, the detection signal output from the FM detection unit 24 combines the modulation component of the reception signal and the frequency component of the first local oscillation signal. The oscillation frequency of the first local oscillation signal is the lower limit frequency of the modulation component. Separation is possible by setting a lower frequency, that is, a frequency lower than the demodulation band.

According to the present embodiment, since the second local oscillation signal is frequency-modulated, it is possible to suppress the baseband signal from being continuously reduced by the reduction unit. Further, since the frequency of the first local oscillation signal from the first local oscillator is set to a frequency lower than the demodulation band, it is possible to suppress the baseband signal from being continuously reduced by the reduction unit regardless of the presence or absence of modulation.

The first local oscillator 90 is a modulation frequency generator that generates a predetermined modulation frequency, and the second local oscillator 92 outputs a second local transmission signal modulated at the predetermined modulation frequency. In other words, since the frequency-modulated second local transmission signal may be output to the quadrature detection unit 12, the modulation frequency may not be generated by the oscillator. For example, if the frequency of the second local oscillator 92 is controlled by a fractional PLL, FM modulation can be performed at a predetermined modulation frequency by setting a frequency division ratio. In this case, a device for setting a frequency division ratio, for example, a CPU can be said to be a modulation frequency generator.

(Example 3)
Next, Example 3 will be described. The third embodiment relates to an FM receiving apparatus that is a direct conversion type and has a coupling capacitor disposed between a quadrature detector and an FM detector, as before. In order to make the frequency of the received signal and the frequency of the local oscillation signal not coincide with each other, in the first embodiment, an offset value is added to the detection signal and then AFC is executed. The control signal is FM modulated. AFC control can only operate after FM detection of the received signal. On the other hand, when the local oscillation signal is FM-modulated, unlike the AFC control, the operation is possible until the reception signal is detected by FM, but the C / N of the local oscillation signal is deteriorated. Reciprocal mixing and S / N tend to deteriorate. In the third embodiment, these are combined, and the processing is switched after the signal detection stage. Before the signal is detected, the local oscillation signal is FM-modulated, and after the signal is detected, AFC control is executed.

FIG. 9 illustrates a configuration of the receiving device 100 according to the third embodiment. The receiving apparatus 100 includes an antenna 10, a quadrature detection unit 12, a first reduction unit 30, a second reduction unit 32, a first ADC unit 14, a second ADC unit 16, a correction unit 34, an FM detection unit 24, an averaging unit 60, and an addition Unit 62, offset storage unit 64, AFC unit 66, DAC unit 68, first local oscillator 90, second local oscillator 92, control unit 94, and selection unit 96. The quadrature detection unit 12 includes a first amplification unit 40, a distribution unit 42, a phase shift unit 44, a first mixer 46, a first LPF unit 48, a second amplification unit 50, a second mixer 52, a second LPF unit 54, and a third amplification. The correction unit 34 includes a first correction unit 18, a second correction unit 20, and a DC correction value detection unit 22, and the AFC unit 66 includes a third LPF unit 70 and a fourth amplification unit 72. Here, it demonstrates centering on the difference from before.

The selection unit 96 inputs the first control signal from the DAC unit 68 and the first local oscillation signal from the first local oscillator 90. Here, the first control signal corresponds to the control signal in the first embodiment. The selection unit 96 also receives a selection signal from the control unit 94. The selection unit 96 selects one of the first control signal and the first local oscillation signal as the second control signal according to the selection signal. The selection unit 96 outputs the selected second control signal to the second local oscillator 92. The second local oscillator 92 adjusts the frequency of the second local oscillation signal in accordance with the second control signal from the selection unit 96, and the second local oscillation signal with the adjusted frequency is sent to the first mixer 46 and the phase shift unit 44. Output to.

The control unit 94 inputs the detection signal from the FM detection unit 24. The control unit 94 generates a selection signal based on the detection signal. The selection signal indicates a signal to be selected by the control unit 94, that is, the first control signal or the first local oscillation signal. Here, the control unit 94 corresponds to monitoring whether the antenna 10 receives an RF signal, that is, monitoring whether a carrier is detected. For example, a noise squelch circuit. The noise squelch circuit detects noise components in a part of the band equal to or higher than the demodulation band of the detection signal output from the FM detection unit 24. If the noise is less than a predetermined level, the noise is suppressed by the carrier and the RF signal is output. It is determined that the signal is received. If the noise is equal to or higher than a predetermined level, it is determined that the RF signal is not received because the noise is not suppressed.

When the RF signal is not received, the control unit 94 generates a selection signal for selecting the first local oscillation signal and outputs the selection signal to the selection unit 96. The selection unit 96 selects the first local oscillation signal based on the selection signal, and inputs a second control signal corresponding to the first local oscillation signal to the second local oscillator 92. As a result, the second local oscillator 92 outputs an FM-modulated second local oscillation signal. In this state, even if an unmodulated signal having the same frequency as the frequency of the second local oscillation signal is received, the I signal and the Q signal do not become constant values, so the baseband signal is not completely suppressed.

In such a situation, when an RF signal is received, the control unit 94 detects this. Here, the oscillation frequency of the first local oscillation signal is multiplexed with the detection signal output from the FM detection unit 24. When the oscillation frequency of the first local oscillation signal is set within the demodulation band, the first local oscillation signal is output as a detection signal and demodulated.

Therefore, when detecting that the RF signal is received, the control unit 94 generates a selection signal for selecting the first control signal and outputs the selection signal to the selection unit 96. The selection unit 96 selects the first control signal based on the selection signal, and inputs the second control signal corresponding to the first control signal to the second local oscillator 92. As a result, the second local oscillator 92 outputs a second local oscillation signal subjected to AFC control. Thereby, even when the oscillation frequency of the second local oscillation signal is within the demodulation band, an unnecessary signal is not included in the detection signal.

That is, the control unit 94 varies the frequency of the second local oscillation signal by generating a selection signal for selecting the first local oscillation signal when no carrier is detected. On the other hand, when detecting the carrier, the control unit 94 switches to a selection signal for selecting the first control signal, thereby stopping the frequency modulation of the second local oscillation signal.

The operation of the receiving apparatus 100 configured as above will be described. FIG. 10 is a flowchart illustrating a control procedure by the receiving apparatus 100. The selection unit 96 selects the first local oscillation signal (S10). If the control unit 94 does not detect a carrier (N in S12), it waits. If the control unit 94 detects a carrier (Y in S12), the selection unit 96 selects the first control signal and the DC correction value detection unit 22 is turned on (S14). If the center frequency of the received signal is positive (Y in S16), the AFC unit 66 performs AFC control to + Δf (S18). On the other hand, if the center frequency of the received signal is not positive (N in S16), the AFC unit 66 performs AFC control to −Δf (S20).

According to the present embodiment, when the RF signal is not received, the FM-modulated second local oscillation signal is output. Therefore, even if an unmodulated signal having the same frequency as the frequency of the second local oscillation signal is received. , I signal and Q signal can be suppressed from becoming constant values. Further, since the I signal and the Q signal do not become constant values, it is possible to suppress the complete suppression. Further, since the first control signal is output when the RF signal is received, it is possible to prevent unnecessary signals from being included in the demodulated signal even when the oscillation frequency of the second local oscillation signal is within the demodulation band. .

The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

10 antenna, 12 quadrature detection unit, 14 1st ADC unit, 16 2nd ADC unit, 18 1st correction unit, 20 2nd correction unit, 22 DC correction value detection unit, 24 FM detection unit, 28 local oscillator, 30 1st reduction Part, 32 second reduction part, 34 correction part, 40 first amplification part, 42 distribution part, 44 phase shift part, 46 first mixer, 48 first LPF part, 50 second amplification part, 52 second mixer, 54 second mixer 2 LPF section, 56 3rd amplification section, 60 averaging section, 62 addition section, 64 offset storage section, 66 AFC section, 68 DAC section, 70 3rd LPF section, 72 4th amplification section, 90 1st local oscillator, 92nd section 2 local oscillators, 94 control units, 96 selection units, 100 receivers .

Claims

A local oscillator that outputs a local oscillation signal;
A quadrature detector that quadrature-detects an FM signal and outputs a baseband signal based on the local oscillation signal output from the local oscillator;
A reduction unit for reducing a direct current component included in a baseband signal output from the quadrature detector;
A correction unit that reproduces a direct current component by correcting the baseband signal so that the origin of polar coordinates is centered on the IQ plane;
An FM detection unit for generating a detection signal by performing FM detection on the baseband signal corrected by the correction unit;
An addition unit that smoothes the detection signal generated in the FM detection unit and adds an offset;
An AFC unit that generates a control signal for controlling the frequency of the local oscillation signal based on the detection signal that has been smoothed and offset, and that feeds back the control signal to the local oscillator;
An FM receiving apparatus comprising:
A quadrature detection of the FM signal based on the local oscillation signal output from the local oscillator, and outputting a baseband signal;
Reducing the DC component contained in the baseband signal;
Regenerating the DC component by correcting the baseband signal so that the origin of polar coordinates is centered on the IQ plane;
FM detecting the corrected baseband signal to generate a detection signal;
Smoothing the generated detection signal and adding an offset;
Generating a control signal for controlling the frequency of the local oscillation signal based on the smoothed and offset-added detection signal, and feeding back the control signal to the local oscillator;
An FM receiving method comprising: