JP7468253B2 - Receiving device - Google Patents

Description

The present invention relates to receiving technology, and in particular to a receiving device for receiving a signal.

In general, a wireless communication device includes a receiving circuit that receives a signal wave transmitted from an external source via an antenna, converts the frequency of the received RF (Radio Frequency) signal to an IF (Intermediate Frequency) signal, and performs demodulation, and an oscillation circuit that outputs a local signal for performing the frequency conversion. The oscillation circuit includes a reference oscillator, and performs PLL (Phase Locked Loop) control using the frequency oscillated by the reference oscillator as the reference frequency. The reference oscillator outputs a reference signal of the reference frequency. Normally, when the reference oscillator oscillates at the reference frequency, it also generates its harmonics. If the harmonics are radiated to the receiving circuit and interfere with the RF signal, this becomes a factor that causes suppression of the receiving sensitivity. Patent Document 1 describes that by changing the reference frequency, the suppression of the receiving sensitivity caused by interference from harmonics can be reduced.

JP 2011-14961 A

However, in a wireless communication device such as that described in Patent Document 1, it is necessary to set whether or not to change the reference frequency depending on the receiving frequency.

The present invention was made in consideration of these circumstances, and its purpose is to provide a technology that automatically reduces the suppression of reception sensitivity caused by harmonic interference.

In order to solve the above problems, a receiving device according to one aspect of the present invention includes a reference oscillator, an oscillation circuit that performs PLL control using the frequency oscillated by the reference oscillator as a reference frequency, a quadrature detector that performs quadrature detection of a received signal using a local signal output by the PLL control in the oscillation circuit, a first high-pass filter that passes high-frequency components in the in-phase components of the received signal quadrature-detected by the quadrature detector, and a second high-pass filter that passes high-frequency components in the quadrature components of the received signal quadrature-detected by the quadrature detector. The frequency oscillated by the reference oscillator is modulated within the band of the loop filter of the oscillation circuit.

In addition, any combination of the above components, and any transformation of the present invention into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present invention.

The present invention can automatically reduce the suppression of reception sensitivity caused by harmonic interference.

FIG. 2 is a diagram illustrating a configuration of a receiving device according to an embodiment. FIG. 2 is a diagram showing the spectrum of a received signal. FIG. 13 is a diagram showing a spurious spectrum due to a reference oscillator. 1A and 1B are diagrams illustrating the spectrum of a received signal and a spurious signal due to a reference oscillator. 1A and 1B are diagrams showing the spectrum of a received signal after detection and a spurious spectrum due to a reference oscillator. 11 is a diagram showing the relationship between the received signal after detection, spurious due to a reference oscillator, and the HPF. FIG. 2 is a diagram showing a spectrum of a local signal output from the oscillator circuit of FIG. 1; 2 is a diagram showing a spectrum of a received signal after detection by the quadrature detector of FIG. 1 and a spurious spectrum due to a reference oscillator. 2 is a diagram showing the relationship between a received signal after detection by the quadrature detector in FIG. 1, a spurious due to a reference oscillator, and an HPF. 1. FIG. 4 is a diagram showing the spectrum of another local signal output from the oscillator circuit of FIG. FIG. 13 is a diagram showing a configuration of a receiving device according to a modified example. FIG. 13 is a diagram showing a configuration of a receiving device according to another modified example.

Before describing the present invention in detail, an overview will be given first. This embodiment relates to a receiving device that receives a wireless signal. The receiving device performs, for example, direct conversion type quadrature detection. The receiving device generates a local signal by PLL control based on the reference frequency of a reference oscillator, and performs quadrature detection of the received signal using the local signal in a mixer. At that time, harmonics generated from the reference oscillator are superimposed on the received signal. By superimposing the harmonics on the received signal, after detection, the spurious interference caused by the harmonics of the reference oscillator interfering with the received signal always becomes DC (Direct Current). As a result, the reception sensitivity is suppressed due to the interference of the harmonics. In order to reduce the spurious interference with the received signal, the in-phase component and quadrature component of the quadrature detected received signal are subjected to HPF (High Pass Filter) processing. However, the received signal is also reduced by the HPF processing, so degradation due to reception distortion occurs. Deterioration in reception distortion can lead to deterioration of received audio and failure to decode signaling such as 2-tone/5-tone.

The receiving device in this embodiment performs low-frequency frequency modulation on the control voltage of the reference oscillator, and a frequency-modulated local signal is input to the mixer. By performing quadrature detection using this local signal, the in-phase and quadrature components of the received signal are also frequency-modulated. The in-phase and quadrature components of the quadrature-detected received signal are HPF-processed to reduce spurious interference with the received signal, but the components of the received signal remain. This reduces the suppression of receiving sensitivity due to spurious, and also reduces degradation due to receiving distortion.

Figure 1 shows the configuration of a receiving device 100. The receiving device 100 includes a modulated signal generator 10, a first filter 12, a reference oscillator 16, an oscillator circuit 18, an antenna 20, a second filter 22, an LNA (Low Noise Amplifier) 24, a third filter 26, a first mixer 28a and a second mixer 28b collectively referred to as mixer 28, a first variable amplifier 30a and a second variable amplifier 30b collectively referred to as variable amplifier 30, a first AAF 32a and a second AAF 32b collectively referred to as AAF (Anti-Aliasing Filter) 32, a first ADC 34a and a second ADC 34b collectively referred to as ADC (Analog to Digital Converter) 34, and a HPF (High Pass Filter). The oscillator circuit 18 includes a first HPF 36a, a second HPF 36b, a fourth filter 38, a fifth filter 40, and a demodulator 42, collectively referred to as a PLL (Phase-Locked Loop) 36. The oscillator circuit 18 includes a PLL 50, a loop filter 52, and a VCO (Voltage-Controlled Oscillator) 54.

Here, the following will be described in the order of (1) the configuration common to the conventional receiving device, (2) problems with the conventional receiving device, and (3) the configuration of this embodiment.
(1) Configuration in common with conventional receiving devices The antenna 20 receives an RF (Radio Frequency) signal from a transmitting device (not shown). The RF signal corresponds to a received signal. The RF signal is, for example, FM modulated, but is not limited to this. The antenna 20 outputs the received RF signal to the second filter 22. The second filter 22 reduces noise components contained in the RF signal. The second filter 22 outputs the RF signal with reduced noise components (hereinafter also referred to as the "RF signal") to the LNA 24.

The LNA 24 amplifies the RF signal from the second filter 22. The LNA 24 outputs the amplified RF signal to the third filter 26. The third filter 26 reduces noise components contained in the amplified RF signal. The third filter 26 reduces the noise components and outputs the amplified RF signal (hereinafter also referred to as the "RF signal") to the first mixer 28a and the second mixer 28b.

The reference oscillator 16 outputs a reference frequency (hereinafter referred to as the "reference frequency") to the oscillation circuit 18. The oscillation circuit 18 executes PLL control based on the reference frequency oscillated by the reference oscillator 16. The PLL control is performed by the PLL 50, the loop filter 52, and the VCO 54, and a local signal is output to the first mixer 28a and the second mixer 28b. Here, the phase of the local signal output to the second mixer 28b is shifted by 90 degrees from the phase of the local signal output to the first mixer 28a.

The first mixer 28a generates an I-phase baseband signal (hereinafter referred to as the "I signal") by multiplying the RF signal from the third filter 26 with the local signal from the oscillator circuit 18. The I signal is an in-phase component of the RF signal. The first mixer 28a outputs the I signal to the first variable amplifier 30a. The second mixer 28b generates a Q-phase baseband signal (hereinafter referred to as the "Q signal") that is orthogonal to the I-phase baseband signal by multiplying the RF signal from the third filter 26 with the local signal from the oscillator circuit 18. The Q signal is an orthogonal component of the RF signal. The second mixer 28b outputs the Q signal to the second variable amplifier 30b. The first mixer 28a and the second mixer 28b correspond to a quadrature detector, and the quadrature detector performs quadrature detection of the RF signal using the local signal.

The first variable amplifier 30a adjusts the level of the I signal. The first variable amplifier 30a outputs the level-adjusted I signal (hereinafter also referred to as the "I signal") to the first AAF 32a. The second variable amplifier 30b adjusts the level of the Q signal. The second variable amplifier 30b outputs the level-adjusted Q signal (hereinafter also referred to as the "Q signal") to the second AAF 32b.

The first AAF 32a performs band limiting on the I signal. The first AAF 32a outputs the band-limited I signal (hereinafter also referred to as the "I signal") to the first ADC 34a. The second AAF 32b performs band limiting on the Q signal. The second AAF 32b outputs the band-limited Q signal (hereinafter also referred to as the "Q signal") to the second ADC 34b.

The first ADC 34a performs analog-to-digital conversion on the I signal from the first AAF 32a. The first ADC 34a outputs the I signal converted into a digital signal (hereinafter also referred to as the "I signal") to the first HPF 36a. The second ADC 34b performs analog-to-digital conversion on the Q signal from the second AAF 32b. The second ADC 34b outputs the Q signal converted into a digital signal (hereinafter also referred to as the "Q signal") to the second HPF 36b. The first ADC 34a and the second ADC 34b can be said to be sampling units that sample the quadrature-detected signal at a predetermined timing.

The first HPF 36a is a filter that passes the high-frequency components of the I signal from the first ADC 34a. The first HPF 36a outputs the high-frequency components of the I signal (hereinafter also referred to as the "I signal") to the fourth filter 38. The second HPF 36b is a filter that passes the high-frequency components of the Q signal from the second ADC 34b. The second HPF 36b outputs the high-frequency components of the Q signal (hereinafter also referred to as the "Q signal") to the fifth filter 40.

The fourth filter 38 performs band limiting on the I signal. The fourth filter 38 outputs the band-limited I signal (hereinafter also referred to as the "I signal") to the demodulator 42. The fifth filter 40 performs band limiting on the Q signal. The fifth filter 40 outputs the band-limited Q signal (hereinafter also referred to as the "Q signal") to the demodulator 42.

The demodulator 42 demodulates the I signal from the fourth filter 38 and the Q signal from the fifth filter 40, and outputs the demodulated audio signal and data. Since any known technology can be used for the demodulation process, a description thereof will be omitted here.

(2) Problems of the conventional receiving device Fig. 2 shows the spectrum of the received signal. This corresponds to the RF signal input to the first mixer 28a and the second mixer 28b in Fig. 1. As shown in the figure, the received signal is, for example, an unmodulated signal. Fig. 3 shows the spectrum of the spurious due to the reference oscillator. This corresponds to the harmonics oscillated from the reference oscillator 16. Here, it is assumed that the frequency of any of the spurious due to the reference oscillator is the same as the frequency of the received signal in Fig. 2. Fig. 4 shows the spectrum of the received signal and the spurious due to the reference oscillator. This is a signal in which the spurious due to the reference oscillator is superimposed on the received signal, and is a signal input to the first mixer 28a and the second mixer 28b in Fig. 1. Any of the spurious due to the reference oscillator overlaps with the received signal.

Figure 5 shows the spectrum of the received signal after detection and the spurious due to the reference oscillator. This is the signal obtained by quadrature detection of the signal in Figure 4, and is the I signal and Q signal mentioned above. As a result of quadrature detection, the spurious due to the reference oscillator and the received signal that interfere with the received signal are output as DC components. In order to reduce the influence of interference due to the spurious due to the reference oscillator, high-frequency components are extracted in the first HPF 36a and the second HPF 36b in Figure 1. Figure 6 shows the relationship between the received signal after detection, the spurious due to the reference oscillator, and the HPF. This shows the frequency characteristics of the HPF 36 in addition to Figure 5. The first HPF 36a and the second HPF 36b remove the spurious due to the reference oscillator that interferes with the received signal. However, the received signal is also removed. In this way, if the received signal is unmodulated, the received signal is completely removed, making it impossible to receive the received signal. Furthermore, if the received signal is a modulated wave, removing the DC component with HPF 36 will increase reception distortion.

(3) Configuration of this embodiment The modulation signal generator 10 in Fig. 1 outputs a modulation signal to the reference oscillator 16 via the first filter 12 to cause the reference oscillator 16 to execute modulation. The modulation signal from the first filter 12 is input to the control voltage terminal of the reference oscillator 16, and the frequency at which the reference oscillator 16 oscillates is frequency modulated by the modulation signal. When the frequency is modulated at a modulation rate of a frequency within the band of the loop filter 52, the local signal output from the oscillation circuit 18 is also frequency modulated. Fig. 7 shows the spectrum of the local signal output from the oscillation circuit 18. As shown in the figure, a frequency modulated local signal is shown. Return to Fig. 1.

The first mixer 28a and the second mixer 28b use a frequency-modulated local signal to perform quadrature detection of the received signal and spurious emissions from the reference oscillator. Figure 8 shows the spectrum of the received signal after detection by the quadrature detector and the spurious emissions from the reference oscillator. This is shown in the same way as Figure 5, but the I and Q signals are frequency modulated, and the components of the spurious emissions from the reference oscillator that interfere with the received signal are DC components.

As explained above, in order to reduce the effects of interference caused by spurious signals from the reference oscillator, high-frequency components are extracted in the first HPF 36a and second HPF 36b in FIG. 1. FIG. 9 shows the relationship between the received signal after detection by the quadrature detector, the spurious signals from the reference oscillator, and the HPFs. The first HPF 36a and second HPF 36b remove spurious signals that interfere with the received signal. Although a portion of the received signal is removed, some remains. In other words, whether the received signal is an unmodulated wave or a modulated wave, the portion of the received signal that is removed by the HPF 36 is reduced. This reduces reception distortion degradation.

Here, when the frequency at which the reference oscillator 16 oscillates is called a first frequency, the frequency of the RF signal is called a second frequency. When the modulation depth of the reference oscillator 16 is m and the modulation depth of the oscillation circuit 18 is n, the following relational expression holds:
n = m × second frequency / first frequency When the modulation depth n of the oscillator circuit 18 is increased, the band of the received signal also widens. If the band of the received signal becomes wider than the passbands of the first HPF 36a, the second HPF 36b, the fourth filter 38, and the fifth filter 40, part of the received signal is removed by the filters, causing distortion and degradation. Therefore, the modulation depth of the reference oscillator 16 is set to an appropriate value.

The modulation signal output from the modulation signal generator 10 may be subjected to a condition where the carrier level of the Bessel function becomes zero. The local signal at that time is frequency modulated under the condition where the carrier level of the Bessel function becomes zero. FIG. 10 shows the spectrum of another local signal output from the oscillator circuit 18. By performing quadrature detection using such a local signal, the DC components of the I and Q signals are reduced. Even if the DC components are removed by the first HPF 36a and the second HPF 36b, the effect of the removal on the received signal is reduced, and the deterioration of the reception distortion is further reduced.

In terms of hardware, this configuration can be realized by the CPU, memory, and other LSIs of any computer, and in terms of software, it can be realized by programs loaded into memory, but here we are illustrating functional blocks that are realized by the cooperation of these. Therefore, those skilled in the art will understand that these functional blocks can be realized in various ways using only hardware, only software, or a combination of both.

Up to now, the receiving device 100 has performed direct conversion, but is not limited to direct conversion. FIG. 11 shows the configuration of the receiving device 100 according to a modified example. The receiving device 100 has the configuration of a low IF receiver. The receiving device 100 further includes an oscillator 60, a first mixer 62a, and a second mixer 62b, which are collectively referred to as mixer 62, in addition to the configuration of FIG. 1. The first mixer 28a and the second mixer 28b generate low IF I and Q signals by performing quadrature detection. The first mixer 62a converts the I signal from low IF to baseband based on the oscillation signal from the oscillator 60. The second mixer 62b converts the Q signal from low IF to baseband based on the oscillation signal from the oscillator 60.

Figure 12 shows the configuration of a receiving device according to another modified example. The receiving device 100 has the configuration of a heterodyne receiver. The receiving device 100 further includes a mixer 70, an MCF 72, an IF amplifier 74, and a variable amplifier 76 in addition to the configuration of Figure 1, and includes a first oscillation circuit 18a and a second oscillation circuit 18b collectively referred to as an oscillation circuit 18. The first oscillation circuit 18a includes a first PLL 50a, a first loop filter 52a, and a first VCO 54a, and the second oscillation circuit 18b includes a second PLL 50b, a second loop filter 52b, and a second VCO 54b. The first PLL 50a and the second PLL 50b are collectively referred to as PLL 50, the first loop filter 52a and the second loop filter 52b are collectively referred to as loop filter 52, and the first VCO 54a and the second VCO 54b are collectively referred to as VCO 54. Since any known technology can be used as a heterodyne receiver, we will not go into detail here.

According to this embodiment, the harmonic components from the reference oscillator are reduced by passing the high-frequency components in the in-phase and quadrature components of the quadrature-detected received signal, so that the suppression of reception sensitivity due to interference from harmonics can be automatically reduced. In addition, since frequency modulation is performed on the reference frequency, the received signal can be frequency modulated by a local signal. In addition, since the received signal is frequency modulated by a local signal, the components removed can be reduced even when the I and Q signals are processed by the HPF. In addition, since the components removed can be reduced even when the I and Q signals are processed by the HPF, reception distortion deterioration can be reduced. In addition, since reception distortion deterioration is reduced, decoding such as 2tone/5tone can be performed. In addition, since a modulation signal for causing the reference oscillator to perform modulation is output to the reference oscillator, modulation in the reference oscillator can be performed. In addition, since the modulation degree of the modulation applied to the reference oscillator is set so that the band of the received signal is within the pass band of the first HPF 36a, the second HPF 36b, the fourth filter 38, and the fifth filter 40, the influence of modulation can be reduced.

The present invention has been described above based on examples. These examples are merely illustrative, and those skilled in the art will understand that various modifications are possible in the combination of each component and each treatment process, and that such modifications are also within the scope of the present invention.

10 Modulation signal generator, 12 First filter, 16 Reference oscillator, 18 Oscillator circuit, 20 Antenna, 22 Second filter, 24 LNA, 26 Third filter, 28 Mixer, 30 Variable amplifier, 32 AAF, 34 ADC, 36 HPF, 38 Fourth filter, 40 Fifth filter, 42 Demodulator, 50 PLL, 52 Loop filter, 54 VCO, 60 Oscillator, 62, 70 Mixer, 72 MCF, 74 IF amplifier, 76 Variable amplifier, 100 Receiver.

Claims (3)

A reference oscillator;
an oscillation circuit that performs PLL control using a frequency oscillated by the reference oscillator as a reference frequency;
a quadrature detector that performs quadrature detection on a received signal using a local signal output by PLL control in the oscillator circuit;
a first high-pass filter that passes a high-frequency component of an in-phase component of a received signal that has been quadrature detected by the quadrature detector;
a second high-pass filter that passes a high-frequency component of the quadrature components of the received signal quadrature-detected by the quadrature detector;
A receiving device, characterized in that the frequency oscillated by said reference oscillator is modulated within the band of a loop filter of said oscillation circuit. The receiving device according to claim 1, further comprising a modulation signal generating unit that outputs a modulation signal to the reference oscillator to cause the reference oscillator to perform modulation. a first band-limiting filter that limits the band of the signal received from the first high-pass filter;
a second band-limiting filter that limits the band of the signal received from the second high-pass filter;
a demodulator that demodulates a signal band-limited by the first band-limiting filter and a signal band-limited by the second band-limiting filter,
3. The receiving device according to claim 1, wherein the modulation depth of the reference oscillator is set so that the band of the received signal is within the bands of the first high-pass filter, the second high-pass filter, the first band-limiting filter, and the second band-limiting filter.

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