JPH104402A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the receiver in which synchronization is obtained precisely at a high speed in digital radio communication. SOLUTION: An antenna 101 receives a radio wave, a tap delay line 102 stores a signal received from the antenna by n-sampling timing, a memory device A105 stores a synchronization word of a desired signal and a correlation device 104 provides an output of a correlation value between the reception signal stored in the tap delay line and the synchronization word of the desired signal stored in the memory device A105. Then the memory device B103 stores the output of the correlation device by m-sampling timing or by the received synchronization words and a synchronization position detector 106 detects the synchronization position based on the result of correlation stored in a memory device B, where n, m are integers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver used for digital TDMA communication, and more particularly to a receiver capable of obtaining good reception performance even in an environment where a large interference signal exists.

[0002]

2. Description of the Related Art A block diagram of a conventional receiver is the same as the block diagram of the receiver according to the first embodiment of the present invention.
As shown in FIG. The receiving apparatus includes an antenna 101 for receiving a radio wave, and a tapped delay line 102 for storing a signal received from the antenna for n sampling timings.
And a first memory device A105 for storing the synchronization word of the desired signal, and a correlation between the received signal stored in the tapped delay line 102 and the synchronization word of the desired signal stored in the first memory device A105, A correlator 104 that provides a good correlation result even when the same frequency interference signal exists; a second memory device B103 that stores the output of the correlator for m sampling timings or a synchronization word time; and a second memory device B103. And a synchronous position detecting device 106 for detecting a synchronous position based on the correlation result stored in the.
However, n and m are integers.

[0003] A case where data is transmitted and received in a frame format as shown in FIG. 2 will be described below.

When transmitting and receiving data, it is necessary to synchronize the transmitting side and the receiving side. Generally, as shown in FIG.
In addition to the original information signal 202 in the signal, a synchronization word 201 for synchronization is inserted, and the reception side correlates the reception signal with the same synchronization word as the transmission side, which is held in advance, and has a high correlation. Let the point be the synchronization position.

[0005] Let R (t) be a received signal sequence, and consider that a synchronization word is just received at time T. The sync word SW _D of the desired _{signal, SW D = {SW D (} 0), SW D (1), SW D (2), SW D (3), ...., SW D (n-1)} Assuming that the correlation value CORR (t) with the received signal at time t is stored in the first memory device A105,

(Equation 1) The correlator 104 calculates this CORR (t) and stores it in the second memory device B103.

FIG. 4 shows CORR (t) when the effects of fading, noise, and multipath are not considered. The correlation value when only the desired signal is included in the received signal is indicated by 401, and the correlation value when only the same frequency interference signal is included is indicated by 402, and the received signal has the same frequency interference signal as the desired signal. Are included at the same power, and the correlation value is indicated by 403. Correlation value where only the same frequency interference wave exists
In the case of 402, since the decoding process cannot be performed even if synchronization is established, it is ignored here. When only the desired signal is included, and when both the desired signal and the same frequency interference signal are included, the highest correlation value is shown at time T.
Synchronous position detecting device 106 outputs a synchronous position detecting signal at time T indicating the highest correlation value as indicated by a circle in FIG. 4, and the receiving device performs demodulation based on the synchronous signal.

[0007]

However, when receiving using the above-described conventional method, considering the effects of fading fluctuation and multipath, the reception power of the same frequency interference signal is less than the reception power of the desired signal. Was sometimes very large.

FIG. 5 shows the result of correlation calculation when the reception power of the desired signal is small and the reception power of the same frequency interference signal is large due to the effect of fading. The correlation value with the desired signal in the case of only the desired signal is indicated by 501, the correlation value in the case of only the same frequency interference signal is indicated by 502, and when the desired signal and the same frequency interference signal are combined with the same power. The correlation value is shown at 503. Originally, the correlation value should be the largest at the time T, but it becomes the largest at the time T-1, and the synchronous position detecting device 106 erroneously detects the synchronous position as the time T-1.

In FIG. 3, since the cross-correlation between the synchronization word of the desired signal and the synchronization word of the same frequency interference signal is relatively high, the correlation value with the desired signal whose correlation value has decreased due to fading fluctuation is relatively high. It is because it becomes big.

[0010] The effects of fading fluctuations are eliminated by averaging the correlation values for each frame. However, during averaging, synchronization cannot be correctly established, and information cannot be received correctly. Therefore, in an environment where co-frequency interference signals are large, such as when an interference canceller is applied to a conventional receiver, synchronization cannot be achieved properly, and signals cannot be received.

[0011]

According to a first aspect of the present invention, there is provided a tapped delay line for delaying and storing a signal received from an antenna, and a first memory device for storing a synchronization word of a desired signal. And calculating a correlation value between a synchronization signal of a received signal stored in the tapped delay line and a synchronization word of a desired signal stored in the first memory device, and obtains a good correlation result even when the same frequency interference signal exists. A second memory device for storing the output of the correlator, and a synchronous position detecting device for generating a synchronous position detection signal based on the correlation value stored in the second memory device. The receiver is characterized in that a correct synchronization position can be detected by using a synchronization word having a small cross-correlation, and the synchronization word is assumed to have the same frequency interference signal. By using a signal having a small cross-correlation, a correlation value with a desired signal can be correctly obtained without performing averaging processing between frames. Therefore, when applied to an apparatus such as an interference canceller, good synchronization performance can be obtained. This has the effect that the reception performance can be improved.

According to a second aspect of the present invention, there is provided a tapped delay line for delaying and storing a received signal from an antenna and a first for storing a synchronization word of a desired signal.
And a third memory device for storing a synchronization word of the same frequency interference signal, and a synchronization word for a received signal stored in the tapped delay line and a desired signal stored in the first memory device. A first correlation device for calculating a correlation value; and a second correlation device for calculating a correlation value of a synchronization word between the received signal stored in the tapped delay line and the same frequency interference signal stored in the third memory device. A correlation device, a second memory device for storing an output of the first correlation device, and a first synchronization position for generating a synchronization position detection signal based on the correlation value stored in the second memory device A detection device, a fourth memory device for storing an output of the second correlation device, and a second synchronization position for generating a synchronization position detection signal based on the correlation value stored in the fourth memory device. A detection device; A synchronous position detection signal is obtained by adding the synchronous positions detected by the first synchronous position detecting device and the second synchronous position detecting device based on the reception power of the same frequency interference signal as the desired signal, and then adding the synchronous positions. And a third synchronous position detecting device for outputting the synchronous position. The synchronous position is obtained from a correlation operation using a synchronous word of the same frequency interference signal even when the same frequency interference signal exists. The detection signal and the synchronization position detection signal obtained from the correlation operation using the synchronization word of the desired signal are weighted by the estimated reception power of the desired signal and the estimated reception power of the interference signal, and the average is obtained. It has a function of obtaining a position detection signal and improving reception performance.

Further, the invention according to claim 3 of the present invention provides:
A first tapped delay line having a plurality of antennas and delaying and storing a received signal from the first antenna;
A second method for delaying and storing the received signal from the second antenna
, A first memory device and a fifth memory device for storing a synchronization word of a desired signal, and a third memory device and a seventh memory device for storing a synchronization word of the same frequency interference signal And a first correlator for calculating a correlation between a received signal from the first antenna stored in the first tapped delay line and a synchronization word of a desired signal stored in the first memory device. And calculating a correlation between a received signal from the first antenna stored in the first tapped delay line and a synchronization word of the same frequency interference signal stored in the third memory device. A correlator, a received word from the second antenna stored in the second tapped delay line and a synchronization word of a desired signal stored in the fifth memory device; Third correlation device for computing the relationship,
A fourth correlator for calculating a correlation between a received signal from the second antenna stored in the second tapped delay line and a synchronization word of the same frequency interference signal stored in the seventh memory device; A second memory device for storing an output of the first correlator, and a first memory for generating a synchronous position detection signal based on the correlation value stored in the second memory device.
And a fourth memory device for storing the output of the second correlation device, and a second memory device for generating a synchronization position detection signal based on the correlation value stored in the fourth memory device. And a sixth memory device for storing the output of the third correlation device, and a fourth memory device for generating a synchronization position detection signal based on the correlation value stored in the sixth memory device. A synchronous position detecting device, an eighth memory device storing the output of the fourth correlating device, and a fifth generating a synchronous position detecting signal based on the correlation value stored in the eighth memory device. , The first synchronous position detecting device, the second synchronous position detecting device, the fourth synchronous position detecting device, and the synchronous position detecting device output by the fifth synchronous position detecting device. The signal is the desired wave of each antenna,
And a third synchronous position detection circuit for outputting a synchronous position detection signal at a time obtained by adding weights for each reception power of the same frequency interference wave. The synchronization position detection signal obtained from the synchronization word of the same frequency interference signal as the synchronization position detection signal obtained from the correlation operation using the synchronization word of the desired signal obtained from the antenna is the desired signal of each antenna, the reception power of the same frequency interference signal. By weighting and averaging, a more accurate synchronous position detection signal can be obtained as compared with the second aspect of the present invention, and the reception performance is improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a block diagram of a receiving apparatus according to a first embodiment of the present invention. In FIG.
The receiving apparatus includes: an antenna 101 for receiving a radio wave; a tapped delay line 102 for storing a signal received from the antenna for n sampling timings; a first memory device A105 for storing a synchronization word of a desired signal; A correlator 104 for correlating the received signal stored in the tapped delay line 102 with the synchronization word of the desired signal stored in the memory device A105, and providing a good correlation result even when the same frequency interference signal exists; A second memory device B103 for storing the output of the correlator for m sampling timings or a synchronization word reception time, and a synchronous position detecting device 106 for detecting a synchronous position based on the correlation result stored in the second memory device B103. It is composed of However, n and m are integers.

A case where data is transmitted and received in a frame format as shown in FIG. 2 as in the conventional example will be described.

When transmitting and receiving data, the transmitting side and the receiving side are synchronized. As shown in FIG. 2, in addition to the original information signal 202, a synchronization word 201 for synchronization is inserted into the signal. On the receiving side, the same synchronization word as the transmitting side, which is held in advance, is correlated with the received signal, and a point having a high correlation is defined as a synchronization position.

It is assumed that a received signal sequence is R (t) and that a synchronization word is just received at time T. Sync word SW _D of the desired signal, the same frequency interference signal SW _{I, respectively, SW D = {SW D (} 0), SW D (1), SW D (2), SW D (3), ..., SW _D (n-1)} SW _I = {SW _I (0), SW _I (1), SW _I (2), SW _I (3), ..., SW _I (n-1)} and receive It is assumed that the signal contains the same frequency interference signal as the desired signal at the same level.

On the receiving side, the synchronization word of the desired signal is
_D is stored in the memory device A105. At this time, for example, a Gold sequence used as a CDMA spreading code is used as the synchronization words SW _D and SW _I in the transmission signal. Alternatively, a Gold sequence is used as a part of the synchronization word. As a result, the cross-correlation between the synchronization words can be suppressed to a small value, and even when the reception power of the desired signal decreases due to fading, the cross-correlation value with the interference signal other than the synchronization position is small, so that the correct synchronization position is detected. It is possible to do.

It is to be noted that generality is not lost even if a sequence other than the Gold sequence that can take a small cross-correlation is used. For example,
The correlation value CORR (t) with the received signal at the time t is as represented by the above-described equation (1). The correlator 104 outputs this CORR (t), and the second memory device B103 stores the value of CORR (t).

When the effects of fading, noise, and multipath are not considered, CORR (t) is as indicated by 403 in FIG. 4 as in the case of using the conventional receiver. Further, the correlation value when the reception power of the desired signal is reduced due to fading is also as indicated by 403 in FIG. This is because the cross-correlation between SW _D and SW _I is small, and the correlation value does not increase even in the case of FIG. Therefore, the synchronous position detecting device 106 can correctly generate a synchronous position detecting signal at the synchronous position T, and the receiving device can correctly receive information.

(Second Embodiment) FIG. 6 shows a second embodiment of the present invention.
FIG. 6 is a block diagram of a receiving device according to the embodiment. In FIG. 6, an antenna 601 for receiving information from a wireless section
And a first memory device A 602 for storing a synchronization word of a desired signal, and a tapped delay line 606 for storing a signal received from the antenna 601 for n sampling timings.
A first correlator A 603 for calculating a correlation value between the synchronization word of the desired signal stored in the first memory device A 602 and the received signal stored in the tapped delay line 606, and a synchronization word of the same frequency interference signal And a tapped delay line and a synchronization word of the same frequency interference signal stored in the third memory device B608.
A second correlator B607 for calculating the correlation value of the received signal stored in 606, and a second memory device A2 (60) for storing the output of the first correlator A603 for m sampling timings.
4) and a fourth memory device B2 (609) for storing the output of the second correlation device B607 for m sampling timings,
A first synchronous position detecting device A605 for detecting a synchronous position based on the correlation result stored in the second memory device A2 (604).
And a second synchronous position detecting device B for detecting a synchronous position based on the correlation result stored in the fourth memory device B2 (609).
610, and a third synchronous position detecting device C611 which weights and outputs the outputs of the first synchronous position detecting device A 605 and the second synchronous position detecting device B 610 from the desired signal and the reception power of the same frequency interference signal. It is configured. FIG.
3 also shows an estimated power 612 of the desired signal obtained as a result of the correlation operation with the synchronization word of the desired signal, and an estimated power 613 of the interference signal obtained as a result of the correlation operation with the synchronization word of the same frequency interference signal. .

The received signal sequence is defined as R (t), and the synchronization word SW _D of the desired signal and the same frequency interference signal SW _I are represented by SW _D = {SW _D (0), SW _D (1), SW _D (2 ), SW _D (3), ..., SW _D (n-1)} SW _I = {SW _I (0), SW _I (1), SW _I (2), SW _I (3), .. ., SW _I (n-1)}, the correlation value between the received signal and the synchronization word of the desired signal
CORR _D (t), the correlation value CORR _I (t) with the same frequency interference signal,
Each

(Equation 2)

(Equation 3) , And are calculated by the first correlator A 603 and the second correlator B 607, respectively.

CORR _D (t) and CORR _I (t) are stored in the second memory device A2 (604) and the fourth memory device B2 (609), respectively, as in the first embodiment. first synchronous position detecting device A605 and the second synchronous position detecting device B610 outputs a sync position detecting timing T _D, T _I.

On the other hand, the first correlator A 603 and the second correlator B 607 use the estimated received power P _D (61) of the desired signal at the times T _D and T _I in the course of the correlation operation between the synchronization word and the received signal.
2), it is possible to obtain the estimated reception power P _I (613) of the same frequency interference signal, and this is used as the synchronous position detection device C611.
Pass on. The synchronous position detecting device C611 outputs the T _D , T _I , P _D , P _I
Using, as the synchronization position time _{T D P D + T I P} I / P D + P I, and outputs a synchronous position detection signal at this time, the receiving apparatus performs demodulation.

When only the desired signal and the interference signal are present, the respective synchronization positions are output. When both the desired signal and the interference signal are present, weighting is performed based on the received power, so that synchronization with higher precision than in the prior art is obtained. It is possible,
The performance of the receiving device can be improved.

In this embodiment, the case where there is one interference signal is shown. However, when there is a possibility that a plurality of interference signals exist, the same operation can be performed by using the synchronization word of another interference signal.

(Third Embodiment) FIG. 7 shows a third embodiment of the present invention.
FIG. 6 is a block diagram of a receiving device according to the embodiment. In FIG. 7, a receiving apparatus includes a first antenna 0 (701) and a second antenna 1 for receiving an information signal from a radio section.
(702), the first memory device A0 (703) and the fifth memory device A1 (70) for storing the synchronization word of the desired signal.
5) and the third memory device B0 (708) and the seventh memory device B for storing the synchronization word of the same frequency interference signal
1 (713), a tapped delay line 0 (706) and a tapped delay line 1 (709) for storing signals received from antennas 0 and 1 for n sampling timings respectively, and a first memory device A0 ( A first correlator A0 (702) for calculating a correlation value between the synchronization word of the desired signal stored in 703) and the received signal stored in the first tapped delay line 0 (706); and a third memory A second correlator B0 that calculates a correlation value between the synchronization word of the same frequency interference signal stored in the device B0 (708) and the received signal stored in the tapped delay line 0 (706).
(707) and a third value for calculating a correlation value between the synchronization word of the desired signal stored in the fifth memory device A1 (714) and the received signal stored in the second tapped delay line 1 (711). The correlation device A1 (710) and the seventh memory device B1 (7
A fourth correlation device B1 (712) for calculating a correlation value between the synchronization word of the same frequency interference signal stored in 13) and the received signal stored in the second tapped delay line 1 (711).
And a second memory device A20 (70) for storing the output of the first correlation device A0 (702) for m sampling timings.
4) and a fourth memory device B20 (71) for storing the output of the second correlation device B0 (707) for m sampling timings.
5) and a sixth memory device A21 (72) for storing the output of the third correlation device A1 (714) for m sampling timings.
5) and an eighth memory device B21 (71) for storing the output of the fourth correlation device B1 (712) for m sampling timings.
6), the first synchronous position detecting device A0 (705) for detecting a synchronous position based on the correlation result stored in the second memory device A20 (704), and the eighth memory device B21 (716). A fifth synchronous position detecting device B1 (720) for detecting a synchronous position based on the stored correlation result, and a fourth memory device B20
A second synchronous position detecting device B0 (717) for detecting a synchronous position based on the correlation result stored in (715), and a synchronous position based on the correlation result stored in the sixth memory device A21 (725). Fourth synchronous position detection device A1 (719) for detecting
The output of the synchronous position detector A0 (705) and the output of the synchronous position detector B0 (717) and the output of the synchronous position detector A1 (719) and the output of the synchronous position detector B1 (720) are the same as the desired signal at each antenna. And a synchronous position detecting device C718 for weighting and outputting the reception power of the frequency interference signal. In this example, the number of antennas is two, but a similar effect can be obtained by using more antennas.

As in the second embodiment, the first synchronous position detecting circuit A0 (705) and the second synchronous position detecting circuit B
0 (717), the fourth synchronous position detection circuit A1 (719), the fifth
The synchronous position timings T _D0 , T _I0 , T _D1 , and T _I1 output from the synchronous position detection circuit B1 (720) are calculated by using the estimated reception power P _D0 (721) of the desired signal at the antenna 0 (701) and the antenna 0 ( 70
The estimated received power P _I0 (72
2) Estimated received power P of desired signal at antenna 1 (709)
_The next time T _D0 P _D0 + T _I0 P _I0 + T _D1 P _D1 + T _I1 P using _D1 (723) and the estimated reception power P _I1 (724) of the same frequency interference signal at antenna 1 (709). _{I1 / P D0 + P I0 +} P D1 + P I1 to the third sync position detecting device C718 outputs the sync position detecting signal, the receiving apparatus performs demodulation.

It is considered that the accuracy is increased by increasing the number of antennas as compared with the second embodiment. Further, in the present embodiment, the case where there is one interference signal is shown, but when there is a possibility that a plurality of interference signals exist, the same operation can be performed using the synchronization word of another interference signal.

[0030]

As described above, the present invention relates to a receiving apparatus for performing communication by synchronizing between a transmitting side and a receiving side.
Synchronization can be performed faster and more accurately than in a conventional receiver, so that reception performance is also improved. By using the receiving device of the present invention, even in an environment where a large interference signal exists,
Since good reception performance can be obtained, it can be used for, for example, an interference canceller or the like. Even when reception power of a desired signal is low due to fading or the like, synchronization can be properly obtained, and there is an effect that higher reception performance can be obtained than before.

[Brief description of the drawings]

FIG. 1 is a block diagram of a receiving device according to a first embodiment of the present invention;

FIG. 2 is a diagram showing a frame format of a signal to be transmitted and received;

FIG. 3 is a diagram showing an example of a case where when a correlation is obtained between synchronization words of the same frequency interference signal and a desired signal, if the cross-correlation is high, a problem occurs.

FIG. 4 is a diagram showing a correlation value between a received signal (sum of a desired signal and the same frequency interference signal) at the time of static characteristics and a synchronization word of the desired signal;

FIG. 5 is a diagram showing a correlation value between a received signal (sum of a desired signal and the same frequency interference signal) at the time of dynamic characteristics and a synchronization word of the desired signal;

FIG. 6 is a block diagram of a receiving device according to a second embodiment of the present invention;

FIG. 7 is a block diagram of a receiving device according to a third embodiment of the present invention.

[Explanation of symbols]

 101, 601, 701, 709 Antenna 102, 606, 706, 711 Tapped delay line 103, 602, 703 First memory device 104 Correlator 105, 604, 704 Second memory device 106 Synchronous position detecting device 603, 702 First correlator 605, 705 First synchronous position detector 607, 707 Second correlator 608, 708 Third memory device 609, 715 Fourth memory device 610, 717 Second synchronous position detector 611, 718 Third synchronous position detecting device 612, 721, 723 Estimated power of desired signal 613, 722, 724 Estimated power of interference signal 710 Third correlator A1 712 Fourth correlator B1 713 Seventh memory device B1 714 Fifth memory device A1 716 Eighth memory device B21 719 Fourth synchronous position detecting device A1 720 Fifth synchronous position detecting device B1 725 Sixth memory device A21

Claims (3)

[Claims] 1. A tapped delay line for delaying and storing a received signal from an antenna, a first memory device for storing a synchronization word of a desired signal, and a received signal stored in the tapped delay line. Calculating a correlation value of a synchronization word of a desired signal stored in the first memory device, and outputting a good correlation result even when the same frequency interference signal exists; and storing an output of the correlator. A second memory device; and a synchronous position detecting device for generating a synchronous position detection signal based on the correlation value stored in the second memory device. Characterized in that the receiving device can detect a signal. 2. A tapped delay line for delaying and storing a received signal from an antenna, a first memory device for storing a synchronization word of a desired signal, and a third memory device for storing a synchronization word of the same frequency interference signal. A memory device, a first correlator for calculating a correlation value between a received signal stored in the tapped delay line and a synchronization word of a desired signal stored in the first memory device; A second correlator for calculating a correlation value between the stored received signal and a synchronization word of the same frequency interference signal stored in the third memory device; and a second correlator for storing an output of the first correlator. A memory device; a first synchronous position detecting device for generating a synchronous position detecting signal based on the correlation value stored in the second memory device; and a fourth synchronous device for storing an output of the second correlating device. Me Memory device, a second synchronous position detecting device for generating a synchronous position detecting signal based on the correlation value stored in the fourth memory device, and the first synchronous position detecting device and the second synchronous position detecting device. A third synchronous position detecting device for outputting a synchronous position detecting signal at a time obtained by weighting the synchronous position detected by the position detecting device based on the reception power of the same frequency interference signal as the desired signal and then adding the weighted signal; A receiving device. 3. A first tapped delay line having a plurality of antennas for delaying and storing a signal received from a first antenna, and a second tap for delaying and storing a signal received from a second antenna. And a first memory device for storing a synchronization word of a desired signal and a fifth memory device.
, A third memory device and a seventh memory device for storing a synchronization word of the same frequency interference signal, and a reception signal from the first antenna stored in the first tapped delay line. And a first correlator for calculating a correlation of a synchronization word of a desired signal stored in the first memory device; and a received signal from the first antenna stored in the first tapped delay line. And a second correlator for calculating a correlation between synchronization words of the same frequency interference signal stored in the third memory device, and the second correlator stored in the second tapped delay line.
A third correlator for calculating the correlation between the received signal from the antenna of the second antenna and the synchronization word of the desired signal stored in the fifth memory device; and a second correlator stored in the second tapped delay line. A fourth correlator for calculating a correlation between a received signal from the antenna and a synchronization word of the same frequency interference signal stored in a seventh memory device, and a second memory device for storing an output of the first correlator A first synchronous position detection device for generating a synchronous position detection signal based on the correlation value stored in the second memory device, and a fourth memory device for storing the output of the second correlation device A second synchronous position detection device for generating a synchronous position detection signal based on the correlation value stored in the fourth memory device, and a sixth memory device for storing the output of the third correlation device And stored in the sixth memory device A fourth synchronous position detecting apparatus for generating a synchronous position detection signal on the basis of the correlation values, and the eighth memory device that stores an output of said fourth correlator, the eighth
A fifth synchronous position detecting device that generates a synchronous position detecting signal based on the correlation value stored in the memory device, the first synchronous position detecting device, the second synchronous position detecting device, and the fourth synchronous position detecting device. Of the synchronous position detection signals respectively output by the synchronous position detecting device and the fifth synchronous position detecting device, weighted for each of the reception powers of the desired wave and the same frequency interference wave of each antenna. And a third synchronous position detection circuit for outputting a signal.