JPH1146151A - Ofdm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress distortion due to improper control caused by a too high power ratio of each OFDM carrier in a DAB mobile receiver. SOLUTION: A demodulation section calculates a power at a center frequency of an OFDM modulation wave, that is at a center point of FFT. A signal relating to the calculated value is fed to an IF stage AGC Amp 52 or the like via a time constant circuit 53. The IF stage AGC Amp 52 or the like amplifies an output of a 2nd stage mixer 22 with respect to a control signal of a prescribed value or over from the time constant circuit 53, the amplified signal is outputted to an IF stage AGC block 23, resulting that an output of an attenuator 21 is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a DAB (Digital Au
OFDM (Orthogonal Freauency Div) such as dio Broadcasting
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM receiver for receiving an ision multiplex broadcast, and more particularly, to an OFDM receiver having an improved AGC function.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional DAB mounted on an automobile or the like.
It is a block diagram of a tuner part of a mobile receiver. This example corresponds to a digitally modulated radio, but the tuner is not significantly different from radios, analog televisions, FMs and AMs, and maintains electrical power while maintaining C / N (carrier power / noise power). It is still intended to amplify the signal to an amplitude level which can be easily processed, to extract only the desired signal, and to transmit the signal faithfully (without distortion) to the demodulation unit.

[0003] 40 is an antenna power supply terminal, 56 is a low-pass filter. The power induced in the antenna element is
It is taken in from the RF input terminal 47, and by the triplexer 1,
L-Band (1452-1492 MHz) currently used in DAB, Ba
The three bands of ndIII (175 to 250 MHz) and BandII (87.5 to 108 MHz) are extracted and sent to the L-Band gain variable RF Amp 30, combiner 2, and input-side BandII tracking double-tuned filter 6, respectively.

[0004] Input-side BandII tracking double-tuned filter
The RF signal sent to 6 is band-limited there, amplified by the Band II gain variable RF Amp 7, and further band-limited by the output Band II tracking double-tuned filter 8, and the first stage Band I
It is sent to I mixer 9.

[0005] L-Ba sent to the variable L-Band gain RF Amp30
After the nd RF signal is amplified, the L-Band mixer 31
The oscillation frequency generated from the crystal 48, the buffer 34, the L-Band PLL block 35, the low-pass filter 33, and the L-Band local oscillator 32 is mixed with a fixed signal, and the band III band RF signal is transmitted to the combiner 2. . The output signal from the L-Band mixer 31 is smoothed after envelope detection by the L-Band AGC block 36, then converted to a DC voltage, and the signal is used to control the gain of the L-Band gain variable RF Amp 30. AGC of L-Band down converter block
A loop is formed.

[0006] The BandIII RF signal sent to the combiner 2 is sent to the input BandIII tracking double-tuned filter 3, band-limited in the same manner as the BandIIRF signal, amplified by the BandIII gain variable RF Amp 4, and then output BandIII tracking complex. The band is limited again by the tuning filter 5, and the first stage B
It is sent to the andIII mixer 10.

Output-side BandII tracking double-tuned filter
8. The band II and Band III RF signals whose band is limited by the output Band III tracking double-tuned filter 5 are each a first-stage PLL.
A block 15, a low-pass filter 20, a buffer 14, a buffer 13, a Band II local oscillator 12, a Band III local oscillator 11, and a transmission line including DATA 41 and CLOCK 42 receive an N value, which is one of the control signals from the system controller, and The signal whose oscillation frequency is variable, which is generated by performing
The ndII mixer 9 and the first-stage BandIII mixer 10 mix. In addition, the tuning voltage transmitted from the low-pass filter 20, which is a control signal for the oscillation frequency of the Band II local oscillator 12 and the Band III local oscillator 11, is input to the input side Ba.
The ndII tracking double-tuned filter 6, the output side BandII tracking double-tuned filter 8, the input side BandIII tracking double-tuned filter 3, and the output side BandIII tracking double-tuned filter 5 are also provided to adjust the center frequency of each to the desired reception frequency. Used for

The signals down-converted to the first-stage IF frequency by the first-stage BandII mixer 9 and the first-stage BandIII mixer 10 are amplified by the first-stage IF 17 for the first-stage IF, and then amplified by the band-pass filter 18 for the first-stage IF. Amplified by the first stage IF 19 for the output side IF
, And is sent to the second-stage mixer 22. On the other hand, the IF signal is envelope-detected by the RF-stage AGC block 16, is smoothed and converted to a DC voltage, and has a BandII gain variable RF Amp7, BandI
This is supplied to the II gain variable RF Amp4 as a gain control signal, and an AGC loop of BandII and BandIII front ends is formed.

First stage IF sent from attenuator 21
The signal is further supplied to the second mixer 22 by the crystal 49 and the IF.
By mixing with a signal generated by the local oscillator 37 and having a fixed oscillation frequency, it is down-converted to a second-stage IF frequency, and the input-side second-stage IF Amp 27, the IF-stage AGC block 23, the envelope detector 24 Sent to

In the IF stage AGC block 23, the second stage mixer 22
After the envelope signal is detected, the signal is smoothed, converted to a direct current, and a signal for controlling the attenuation of the attenuator 21 is sent out.

The second stage I sent to the input side second stage IF Amp27
The F signal is then amplified and the second-stage IF bandpass filter 28
In the second stage IF 29 for the output side, the signal is amplified to the signal level suitable for the demodulation unit, and the IF output terminal 45
Sent to

The second-stage IF signal sent to the envelope detector (RSSI block) 24 is subjected to envelope detection there, and the low-pass filter 25 at the next stage limits the frequency band above the frequency of the second IF. Thereafter, the signal is sent to the RSSI output terminal 46 via the buffer 26 as an RSSI signal which is a synchronization signal of the demodulation unit.

An AFC control signal having information on the frequency offset amount is sent from the demodulation unit to the AFC control terminal 44, and the oscillation frequency of the reference local oscillator 39 is finely controlled. Then, the output signal of the reference local oscillator 39 is subjected to high-precision tuning to a desired signal after the harmonics are removed by a band-pass filter 38 and supplied to the first-stage PLL block 15 as a reference frequency source. Will be In addition, PLL
Is sent from the lock terminal 43 to the outside (for example, a microcomputer).

[0014]

In the closed loop according to the AGC blocks 16, 23, and 36 of the conventional DAB mobile receiver, the distortion caused by the excessive input level, which is located on the reception signal line in the loop, is obtained. An operation is performed so that the output level of the device whose occurrence is to be suppressed is constant. However, since the operation indirectly prevents the occurrence of distortion, since the operation is not performed by directly sensing the amount of distortion, the circuit characteristics (mainly the dynamic range with respect to the input signal level of the active circuit) depend on the temperature. Frequency-selective fading, which is caused by fluctuations in the detection efficiency of the envelope detector) or by a plurality of carriers such as OFDM modulated waves and a wide bandwidth occupied by the plurality of carriers. The function is sufficient for suppressing distortion due to improper control when the power ratio of each carrier constituting the multicarrier at the time is excessive, and also at the time of the third-order intermodulation interference by the undesired OFDM wave. I couldn't say.

An object of the present invention is to provide an OFDM receiver which overcomes the above problems.

[0016]

The OFDM receiver according to the present invention has the following (a) to (c). (A) Amplitude changing means (4, 7, 21, 30) for changing the amplitude of an OFDM signal in the tuner stage at an amplitude change rate corresponding to the amount of AGC feedback from the output side in the tuner stage (b) OFDM in the demodulation stage Power detection means for detecting power at FFT point points not corresponding to OFDM carriers based on signal demodulation. (C) To amplitude changing means (4, 7, 21, 30) so that the detection amount of power detection means decreases. AGC amount correction means (50, 51, 52) for correcting the amount of AGC feedback based on the output of the power detection means

The amplitude changing means (4, 7, 21, 30) includes an amplifier and an attenuator. In addition, the amplitude changing means (4, 7, 21,
The amplitude change rate of 30) is a gain for an amplifier and an attenuation rate for an attenuator.

In the OFDM demodulation unit, the multicarrier IF signal transmitted from the tuner unit is converted into a digital signal by an AD converter, and the OFDM wave such as IQ demodulation and FFT is demodulated. As one of the demodulation results, the level of each carrier constituting the multicarrier is also calculated.
The number of points is, of course, 2 ^ N (where ^ N means the Nth power and N is an integer), and the number of points that is equal to or greater than the number of OFDM modulated wave multicarriers and 2 ^ N in the demodulation unit With FFT
Processing is being performed. However, DAB (Digital Au
dio Broadcasting) and DVB (Digital Video Bro
In the OFDM modulation of the existing broadcasting system such as adcasting, the center carrier corresponding to the center frequency is not provided, but the power level of a point that should not exist originally is calculated by the third-order intermodulation interference level or the like. The amplitude change rate of the amplitude change means (4, 7, 21, 30) is controlled based on the power of the FFT point point that should not exist, and the distortion level affects the reliability of information on signal demodulation. The amplitude changing rate of the amplitude changing means (4, 7, 21, 30) inside the tuner can be changed so that the area hardly affects (the bit error rate is deteriorated). Therefore, this leads to a reduction in the margin for distortion of the transfer level to the amplifier, attenuator, mixer, etc. in the design of the level diagram in the tuner (line design), and the minimum sensitivity, C / N (carrier power / noise) It is possible to improve the reliability of received information due to the improvement in power).

Further, an RF stage (RF IN
(Between the first and second mixers) AGC can be set to a small amount to reduce the amount of AGC attenuation. Therefore, it is possible to reduce the sensitivity suppression phenomenon (a case in which the required power of the desired wave is lost due to the attenuation generated in the attenuator constituting the AGC).

Further, since the AGC operation corresponding to the third-order intermodulation interference level is enabled, the power level difference between the multi-carriers is reduced as in the case of frequency selective fading when receiving an OFDM wave as a terrestrial wave. C / N degradation due to excessive attenuation in large cases (optimizing the transfer level to active devices is not simple),
Alternatively, the amount of distortion generated due to insufficient attenuation can be reduced.

The OFDM receiver according to the present invention has a delay means (53) for delaying the output of the power detection means and sending it to the AGC amount correction means (50, 51, 52).

The delay means (53) appropriately delays a signal sent from the power detection means to the AGC amount correction means (50, 51, 52), and abruptly changes the output of the power detection means. Suppress control fluctuation.

According to the OFDM receiver of the present invention, the amplitude changing means (4, 7) includes an RF signal amplifier (4, 7) for amplifying the RF signal.
7).

According to the OFDM receiver of the present invention, the amplitude changing means (21) is an IF signal attenuator (21) for attenuating an IF signal.

According to the OFDM receiver of the present invention, the first
A mixer (31) for down-converting the RF signal of the first band to the band of another RF signal of the second band, and an amplitude changing means (30) amplifying the RF signal of the first band to a mixer (31). The RF amplifier (30) for the frequency conversion unit to be sent to (31).

According to the OFDM receiver of the present invention, the first
A mixer (31) for down-converting the RF signal of the second band to the band of the RF signal of another second band, and an amplitude changing means (4, 7, 21, 30) for providing an RF signal for amplifying the RF signal Amplifiers (4, 7), IF signal attenuators (2
1), and amplifies the RF signal of the first band and a mixer (31)
Including the frequency conversion unit RF amplifier (30) to send to, AGC amount correction means (50, 51, 52), attenuator for IF signal (21), corresponding to small, medium, and large detection power of the power detection means, Next, an RF signal amplifier (4, 7), and finally, a frequency converter RF amplifier (30),
The corrected AGC feedback amount based on the output of the power detection means is sent so that the AGC feedback amount increases in order from the latter stage.

The change in the amplitude of the OFDM signal has a greater effect on the demodulation stage as the change in the amplitude by the preceding amplitude changing means (4, 7, 21, 30). Depending on the detection power of the power detection means, small, medium, and large, A is used in the order of the attenuator for the IF signal (21), the amplifier for the RF signal (4, 7), and the RF amplifier (30) for the frequency conversion unit from the rear stage
By receiving control to increase the amount of AGC feedback by the GC amount correcting means (50, 51, 52), it is possible to perform appropriate AGC control according to the magnitude of intermodulation interference caused by multicarriers. Further, since the amplitude change rate is of a form in which the amount of AGC feedback to the amplitude change means (4, 7, 21, 30) is corrected based on the output of the power detection means, the AGC feedback amount from the output side in the tuner stage is adjusted. The AGC based on the output of the power detection means is performed in parallel while the original AGC based on the amount is performed.

According to the OFDM receiver of the present invention, OFDM
The FFT point point not corresponding to the carrier is the center frequency of the OFDM modulated wave.

Since the third-order intermodulation interference appears most at the center frequency of the OFDM modulated wave, the magnitude of the intermodulation interference caused by the multicarrier can be accurately detected by the power at the center frequency of the OFDM modulated wave.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is mounted on a car etc.
It is a block diagram of the tuner part of a DAB mobile receiver. Four
0 is an antenna power supply terminal, and 56 is a low-pass filter. R
The power induced in the antenna element is taken from the F input terminal 47, and the triplexer 1 uses the L-Band (1452 to 1492MHz) and BandIII (175 to 250MHz) currently used in DAB.
z), three bands of BandII (87.5-108MHz) were extracted, and L-Band gain variable RF Amp30, combiner 2,
The input band II tracking is sent to the double tuning filter 6.

Input-side BandII tracking double-tuned filter
The RF signal sent to 6 is band-limited there and amplified by Band II gain variable RF Amp7. The amplified BandIIRF signal is further band-limited by the output-side BandII tracking double-tuned filter 8 and sent to the first-stage BandII mixer 9.

L-Ba sent to variable L-Band gain RF Amp30
After the nd RF signal is amplified, the L-Band mixer 31
After being mixed with the signal generated by the buffer 34, the L-Band PLL block 35, the low-pass filter 33, the L-Band local oscillator 32, and the like, and down-converted to a Band III band RF signal,
It is sent to combiner 2. Also, L-Band mixer 31
After the output signal from the L-Band AGC Amp50 gains a specific gain, after the envelope detection in the L-Band AGC block 36,
Smoothed, converted to DC voltage and variable L-Band gain RFAmp3
The operation is to control the gain of 0, and the AGC loop of the L-Band down converter block is formed.

The BandIII RF signal sent from the triplexer 1 or from the L-Band mixer 31 to the combiner 2 is band-limited by the input BandIII tracking double-tuned filter 3 and amplified by the BandIII gain variable RF Amp4. The amplified BandIII RF signal is further band-limited by the output BandIII tracking double-tuned filter 5, and sent to the first-stage BandIII mixer 10.

A transmission line composed of DATA 41 and CLOCK 42 for receiving an N value which is one of control signals from the system controller, a first-stage PLL block 15, a low-pass filter 20, a buffer 14, a buffer 13, a Band II local oscillator 12
Alternatively, a local signal having a variable oscillation frequency generated by synthesized tuning by the Band III local oscillator 11 is transmitted to the first-stage Band II mixer 9 and the first-stage Band III mixer 10. Then, the band-limited BandIII and BandII from the output-side BandIII tracking double-tuned filter 5 and the output-side BandII tracking double-tuned filter 8 are output.
The RF signals are the first-stage BandIII mixer 10 and the first-stage BandI
The mixture is mixed in the I mixer 9.

The signals down-converted to the first-stage IF frequency by the first-stage BandII mixer 9 and the first-stage BandIII mixer 10 are amplified by the first-stage IF 17 for the first-stage IF. The first-stage IF band-pass filter 18 is suitable for narrow band limitation corresponding to the occupied bandwidth of a certain broadcast signal (for example, 1.5 MHz in the case of DAB), and is amplified again by the output first-stage IF 19 After passing through the attenuator 21, it is sent to the second-stage mixer 22.

On the other hand, the first-stage IF signal amplified by the RF-stage AGC Amp 51 is envelope-detected by the RF-stage AGC block 16, smoothed, converted to a DC voltage, and used as a gain control signal with a variable Band II gain. Provided to RF Amp7 and BandIII variable gain RF Amp4. This closed loop is BandII, BandI
It will be the front-end AGC for II.

The first stage IF sent from the attenuator 21
The signal is further supplied to the second stage mixer 22 by the IF local oscillator.
The signal 37 is mixed with a signal generated by the reference local oscillator 49 and down-converted to a second-stage IF signal. Thereafter, the signal is sent to the input-side second-stage IF Amp 27, IF-stage AGCAmp 52, and envelope detector 28.

The second-stage IF signal sent to the IF-stage AGC Amp 52 is amplified there, envelope-detected by the IF-stage AGC block 23, smoothed, converted into a DC current, and used as a signal for controlling the amount of attenuation. Is sent to the attenuator 21. This closed loop becomes the AGC of the IF stage centering on the second stage mixer 22.

The second stage I sent to the input side second stage IF Amp27
After the F signal is amplified there, the second-stage IF bandpass filter 2
In 8, the band is limited in a narrow band close to the characteristics of the first-stage IF band-pass filter 18, and finally the output-side second-stage IF 29
Then, the signal is amplified to a signal level suitable for a subsequent demodulation unit (for example, an AD converter), and sent to an IF output terminal 54.

The second-stage IF sent to the envelope detector 28
The signal is then envelope-detected and the next stage low-pass filter
At 25, the band above the frequency of the second stage IF is restricted. After that, it becomes a time synchronization signal of the demodulation unit via the buffer 26.
As RSSI (Received Signal Strength Indicator) signal
It is sent from the RSSI output terminal 46 to the demodulation unit.

An AFC control signal having a frequency offset amount (a DC voltage when the reference local oscillator is voltage-controlled) is sent from the demodulation unit to the AFC control terminal 44, and during mobile reception, the center frequency of the desired wave is adjusted. Fine control of the oscillation frequency of the reference local oscillator 39 is performed every moment with respect to the Doppler shift. Then, the output signal of the reference local oscillator 39 is subjected to harmonic removal by a band-pass filter 38, and then supplied to the first-stage PLL block 15 as a reference frequency source, thereby performing highly accurate tuning to a desired signal. Will be

In the subsequent demodulation section, the second-stage multicarrier IF signal transmitted from the IF output terminal 45 is converted into a digital signal by an AD converter, and OFDM waves such as IQ demodulation and FFT are demodulated. As one of the demodulation results, the level of each carrier constituting the multicarrier is also calculated, but the number of FFT points is naturally 2 ^ N (^ N means Nth power, N is an integer). In the demodulation unit, the FFT is performed with the number of points equal to or greater than the number of multicarriers of the OFDM modulated wave and 2 ^ N
Processing is being performed. However, in the existing broadcast system OFDM modulation such as DAB and DVB (Digital Video Broadcasting), since the center carrier corresponding to the center frequency is not provided, the actual receiver calculates the power level of the point that should not exist originally Will be.

FIG. 2 is a power spectrum diagram of the IF signal output from the tuner unit to the demodulation unit. Solid bars are OF
It corresponds to each carrier of DM. Each dashed bar corresponds to a third order intermod. The power level is subjected to a process such as Sk → ak + jbk (k: 1 to + −N / 2, N: the number of multicarriers) for each carrier in the process of the FFT calculation process after IQ demodulation in the demodulation unit. Pk = √ (ak
The power level Pk is calculated from (2 + b2). 3rd-order intermodulation interference with the highest power, that is, IM 3RD 0 (InterModurati
on 3rd order) appears at the center frequency of the OFDM modulated wave, and P0
Corresponding to An additional note is made on third-order intermodulation interference. The relationship between the input voltage Vi and the output signal Io in the active device is as shown in the following equation (1). Here, ^ indicates a power, and ^ 2, ^ 3, ... mean square, third power, .... (1): Io = a0 + a1 · Vi + a2 · Vi ^ 2 + a3 · Vi ^ 3
＋ ・ ・ ・

Consider the case of three signals ω1, ω2, ω3. 3
The next term is expressed by the following equation (2). (2): a3 · Vi ^ 3 = a3 · (V1 · sin ω1t + V2 ·
sinω2t + V3 · sinω3t) ^ 3

When the equation (2) is expanded, the term of the maximum coefficient of a3 becomes the following equation (3). (3): 6 ・ a3 ・ V1 ・ V2 ・ V3 ・ sinω1t ・ si
nω2t ・ sinω3t

When the equation (3) is rewritten into a linear equation, the following equation (4) is obtained. (4): (3/2) · V1 · V2 · V3 ｛sin (ω1−ω
2 + ω3) t-sin (ω1-ω2-ω3) t-sin (ω1
+ Ω2 + ω3) t + sin (ω1 + ω2-ω3) t｝

From equation (4), it can be seen that among the distortion components of the third order, distortion occurs in which the frequency difference between the undistorted signals is offset from the original signal. When carriers are arranged at equal intervals as in OFDM, third-order distortion occurs at equal intervals of the carriers, and the sum of distortions is maximized at the center frequency without modulated multicarriers due to the number of combinations. It turns out that it becomes.

Returning to FIG. 1, in this DAB mobile receiver,
Using the fact that the center frequency is the point where the sum of the third-order intermodulation interference caused by the multicarrier of the desired wave itself is the largest, or the combination of the relationship is the most frequent point,
The demodulation unit converts the calculated value from DA to AG and converts it to a DC voltage signal.
It is sent to the C control terminal 54. On the tuner side, a time constant circuit 53 provided for the purpose of removing unnecessary harmonic components of the signal sent to the AGC control terminal 54 and for preventing abrupt fluctuations in the operation of the AGC loop to be controlled is desired to meet the design specifications. The same control signal for L-Band after satisfying the characteristics of
It is transmitted to AGC Amp50, AGC Amp51 for RF stage, and AGC Amp52 for IF stage.

FIG. 3 shows an IM 3RD 0 (Inter Modurat) in the demodulation unit.
3 shows the relationship between the 3rd order) and the DC voltage at the IF output terminal 54. The DC voltage at the IF output terminal 54 increases as the amount of power of the IM 3RD0 increases. In FIG. 3, “from the demodulation unit
Since the trajectory of "AGC control voltage characteristic" is an output from a DA converter with a certain number of quantization bits, the horizontal axis is IM3R
When expressed as D 0, that is, as a level calculation value at the center frequency, it has a stepped shape. In addition, the gain of each AGC Amp is set in two ways, and the threshold values at which the gain of each AGC Amp changes are set in order from the rear stage, and the AGC Amp 52 for the IF stage is AV, R
The AGC Amp51 for F-stage becomes BV and the AGC Amp50 for L-Band becomes CV. I
AGC Amp52 for F stage, AGC Amp51 for RF stage, and AGC A for L-Band
When mp50 is turned on, AGC Amp52 for IF stage, AGC Amp for RF stage
51, and AGC Amp50 for L-Band to IF stage AGC block 23, RF
The control amount to the stage AGC block 16 and the L-Band AGC block 36 increases, and as a result, the attenuation amount of the attenuator 21 increases, and the Band III gain variable RF Amp4 and the Band II gain variable RF
The amplification amount of Amp7 decreases, and the amplification amount of L-Band variable gain RF Amp30 decreases. With this configuration and setting, the control voltage from the demodulation unit increases in proportion to the power detection level of the center frequency in the demodulation unit while the normal analog AGC loop is operated. 3 when receiving Band
Stage) The signal level held down by the AGC decreases.

By operating according to the increase or decrease of the power corresponding to the direct third-order intermodulation distortion, a gain and a gain for preventing the distortion, which is the original purpose, as compared with the conventional method are obtained.
This is an operation for controlling.

[Brief description of the drawings]

FIG. 1 is a block diagram of a tuner section of a DAB mobile receiver mounted on an automobile or the like.

FIG. 2 is an IF output from a tuner unit to a demodulation unit;
It is a power spectrum diagram of a signal.

FIG. 3 is a diagram illustrating an IM 3RD 0 (Inter Moduration) in a demodulation unit.
3rd order) and the DC voltage of IF output terminal 54.

FIG. 4 is a block diagram of a tuner section of a conventional DAB mobile receiver mounted on an automobile or the like.

[Explanation of symbols]

4 Band III gain variable RF Amp (amplitude changing means, RF signal amplifier) 7 BandII gain variable RF Amp (amplitude changing means, RF signal amplifier) 21 Attenuator (amplitude changing means, IF signal attenuator) 30 L-Band gain variable RF Amp (amplitude changing means, frequency conversion section RF amplifier) 31 L-Band mixer (mixer) 50 AGC Amp for L-Band (AGC amount correcting means) 51 AGC Amp for RF stage (AGC amount correcting means) 52 for IF stage AGC Amp (AGC amount correction means) 53 Time constant circuit (delay means)

Claims (7)

[Claims] (A) amplitude changing means (4, 7, 21, 30) for changing the amplitude of an OFDM signal in a tuner stage at an amplitude change rate according to an AGC feedback amount from an output side in the tuner stage;
(B) power detection means for detecting power at an FFT point point not corresponding to an OFDM carrier based on demodulation of an OFDM signal in a demodulation stage; and (c) changing the amplitude so that the detection amount of the power detection means decreases. AGC for correcting the amount of AGC feedback to the means (4, 7, 21, 30) based on the output of the power detection means
An OFDM receiver characterized by having an amount correcting means (50, 51, 52). 2. The apparatus according to claim 1, further comprising a delay unit (53) for delaying an output of the power detection unit and sending the output to the AGC amount correction unit (50, 51, 52). OFDM receiver. 3. The OFDM receiver according to claim 1, wherein said amplitude changing means is an RF signal amplifier for amplifying an RF signal. 4. The OFDM receiver according to claim 1, wherein said amplitude changing means is an IF signal attenuator for attenuating an IF signal. 5. A mixer for down-converting an RF signal of a first band into another band of an RF signal of a second band.
Is provided, and the amplitude changing means (30) is provided for the first band.
Frequency converter for amplifying an RF signal and sending it to the mixer (31)
6. An OFDM receiver according to claim 1, wherein said receiver is an RF amplifier. 6. A mixer for down-converting a first band RF signal to another second band RF signal band.
The amplitude changing means (4, 7, 21, 30) is an RF signal amplifier (4, 7) for amplifying an RF signal, and an IF for attenuating an IF signal.
A signal attenuator (21), and a frequency converter RF amplifier (30) for amplifying and sending the first band RF signal to the mixer (31), and the AGC amount correcting means (50, 51, 52) The IF signal attenuator (21), then the RF signal amplifier (4, 7), and finally the frequency conversion unit RF, corresponding to the small, medium, and large detection power levels of the power detection means. Amplifier (30)
3. The OFDM receiver according to claim 1, wherein a corrected AGC feedback amount based on an output of the power detection means is transmitted such that the AGC feedback amount increases in order from a subsequent stage. 7. The OFDM receiver according to claim 1, wherein the FFT point point that does not correspond to an OFDM carrier is a center frequency of an OFDM modulated wave.