JP2006148592A - Cofdm modulation signal receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a COFDM modulation signal receiver capable of always keeping information quality of a received signal excellently by optimizing an analog baseband signal level applied to a demodulation section and an input level applied to a mixer in each stage of the receiver at all times. <P>SOLUTION: An intermodulation disturbance level detected when the level of the analog baseband signal is digitally demodulated by the demodulation section 60 is fed back as an AGC control signal to a gain variable RF amplifier 25, a gain variable RF amplifier 4, and an attenuator 17 for carrying out AGC control using an analog detection signal in each of a Hi-BAND stage, an RF stage, and an IF stage. Thus, the AGC control can be applied to the demodulation section 60 in a way that a prescribed input value of the analog baseband signal applied to the demodulation section 60 and the input level to the mixer of each stage are changed so as to lower the intermodulation disturbance level, and both the enhanced reception sensitivity and the reduction in distortion in the receiver can be realized. Consequently, the receiver can always keep the information quality of the received signal excellently at all times. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a COFDM modulated signal receiver, and more particularly, to an AGC (Automatic Gain Control) that holds an input level to a demodulation unit of an analog baseband signal obtained by converting a received COFDM modulated signal at a predetermined value.

  As an example of a conventional COFDM modulated signal receiver, a DAB mobile receiver that has been internationally standardized earliest in COFDM will be described. FIG. 3 shows the reception of DAB (“ETS300401”), which is an existing COFDM modulation system broadcast (which has already started in Europe, Canada, and Australia, excluding the former socialist sphere), which is also installed in mobile objects such as automobiles. It is the block diagram which showed the structure of the tuner part of a machine (for example, refer patent document 1). This example belongs to the category of digital audio radio using the COFDM modulation system, but the tuner section is not much different from conventional amateur radio equipment or analog NTSC / PAL / SECAM television, FM, AM radio, The objective is to amplify the C / N of the desired signal received by the antenna without losing it as much as possible, and send it to the demodulator as the signal processor at the subsequent stage.

  In FIG. 3, first, power induced in an antenna element (not shown) is taken in from an RF input terminal 45, and L-Band (1452 to 1492 MHz) and Band3 (175 to 240 or 250 MHz) used in an existing DAB by the duplexer 1 are used. Are extracted and sent to the L-band gain variable RF amplifier 25 and the combiner 2, respectively. At this time, a DC current is supplied from the antenna DC supply terminal 35 to the antenna element via the low-pass filter 37.

  The signal sent to the L-Band gain variable RF amplifier 25 is amplified here, and then output from the L-Band local oscillator 27 controlled by the L-Band PLL block 30 in the L-Band mixer 26. To be an RF signal in the Band 3 frequency band, and further sent to the first tracking filter 3 via the combiner 2. On the other hand, the output signal from the L-Band mixer 26 is envelope-detected by the AGC block 31, and the DC signal controls the gain of the L-Band gain variable RF amplifier 25, and the RF signal in the Band3 frequency band. An AGC loop is formed to control so that the input level is optimized.

  After the Band 3 RF signal sent to the combiner 2 is sent to the first tracking filter 3 (many of which the single-tuning type is used) and subjected to band limitation, it is amplified by the Band 3 gain variable amplifier 4. The second tracking filter 5 is subjected to band limitation again and sent to the first mixer 6.

  The RF signal band-limited by the second tracking filter 5 is mixed with the DC signal generated by the PLL block 10, the low-pass filter 15, the RF stage local oscillator 7, and the buffer amplifier 9 by the first mixer 6. The first IF signal is sent to the first IF amplifier 12. The DC signal generated for controlling the oscillation frequency of the RF stage local oscillator 7 is also applied to the first tracking filter 3 and the second tracking filter 5 of the RF stage to control the center frequency of the pass band. To be used together.

  The signal down-converted to the first IF frequency is amplified by the first IF amplifier 12 and then narrowed by the first IF bandpass filter (fixed type) 13 as compared with the processing in the RF stage. Receive limited bandwidth. The first IF frequency signal subjected to the band limitation is amplified again by the second IF amplifier 14, passes through the attenuator 16, and is then sent to the second mixer 17.

  On the other hand, the signal down-converted by the first mixer 6 is extracted by the RF stage AGC block 11 where it is subjected to envelope detection to become a DC signal, which is applied to the gain variable RF amplifier 4. As a result, an AGC loop is built and the gain of the RF signal is adjusted.

  Further, the second mixer 17 mixes the input RF signal and a fixed frequency signal generated by the combination of the crystal 20 and the local oscillator 32, down-converts a certain frequency, and performs the second conversion. The IF signal is input to the second IF stage AGC block 18, the RSSI block 19, and the second IF amplifier 22. The IF signal is extracted by the IF stage AGC block 18 and subjected to envelope detection to become a DC signal. When the signal is applied to the attenuator 16, another AGC loop is formed, The gain of the IF signal 2 is adjusted.

  After the signal sent to the second IF amplifier 22 is amplified, it is subjected to the final narrowband restriction by the second IF bandpass filter (fixed type) 23 in the next stage, and is illustrated by the second IF amplifier 24. Amplified to a signal level suitable for the input range of the demodulator, which is not transmitted, and is sent from the IF output terminal 40 to the demodulator as an analog baseband signal of the receiver.

  On the other hand, the second IF signal sent out from the second mixer 17 is also applied to an RSSI (Received Signal Strength Detector) block 19, subjected to envelope detection with a small time constant, and then passed through a low-pass filter 41. The high-frequency component is removed, and it is output from the RSSI output terminal 42 as an RSSI signal required by the subsequent demodulator at the initial stage of synchronization (timing synchronization with the burst signal) via the buffer amplifier 21.

The communication terminal with the external system controller has, for example, three terminals (DATA 36, CLOCK 37, LOCK 38) for controlling the N value of the PLL block 10 and recognizing the PLL lock in the I2C (eye squarer) bus. An AFC terminal 39 is provided for fine frequency tuning from the subsequent demodulator.
JP 11-46154 A (page 5-6, FIG. 1)

  However, in each of the AGC control loops provided in the Hi-Band, RF stage, and first IF stage in the above-described conventional COFDM modulated signal receiver, analog detection (envelope detection) is performed by the AGC blocks 31, 11, and 18. Since the AGC control is performed only according to the selected level, and the total power of the COFDM modulated signal is controlled accordingly, even if intermodulation interference between multicarriers is caused by the nonlinearity inside the receiving module, the demodulator Only a total signal of a predetermined level is input from the terminal 40, and the input level to the ADC block, which is the first stage of the demodulator, is not always optimally maintained against the generation of distortion components. There is a problem that BER (Bit Error Rate), which is an indicator of signal information quality, deteriorates.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to always optimize the analog baseband signal level to the demodulator and always keep the information quality of the received signal good. It is an object of the present invention to provide a COFDM modulated signal receiver.

  In order to achieve the above-mentioned object, the present invention achieves analog detection of each of the Hi-BAND stage, the RF stage, and the IF stage when receiving a COFDM modulated wave of a desired channel and inputting it as an analog baseband signal to the demodulation unit. A COFDM signal receiver that holds the analog baseband signal level input to the demodulator at a predetermined value by providing each stage with an AGC loop controlled by a signal, wherein the analog baseband signal Detecting means for detecting an intermodulation interference level when the demodulator digitally demodulates the level, and feeding back the detected intermodulation interference level to the AGC loop of each stage as an AGC control signal. Feedback means for varying the predetermined input value of the signal to the demodulator. That.

  As described above, in the COFDM modulated signal receiver according to the present invention, in addition to performing AGC control of each stage with the analog detection signals of each stage of the Hi-BAND stage, the RF stage, and the IF stage, when the digital demodulation is performed by the demodulation unit By detecting the intermodulation interference level and feeding it back to the AGC control loop of each stage as an AGC control signal, the predetermined input value to the demodulator of the analog baseband signal is changed so that the intermodulation interference level is lowered. By performing the AGC control, it is possible to always optimize the analog baseband signal level to the demodulator and keep the information quality of the received signal good.

  According to the present invention, in addition to performing AGC control of each stage by the analog detection signal of each stage of the Hi-BAND stage, RF stage, and IF stage, the intermodulation interference level detected when digital demodulation is performed by the demodulator. Is fed back to the AGC control loop of each stage as an AGC control signal, so that the analog baseband signal level to the demodulator is always optimized to significantly reduce the deterioration of the BER, which is an indicator of the information quality of the received signal. As a result, the information quality of the received signal can always be kept good.

  AGC control of each stage by analog detection signal of each stage in BAND stage, RF stage, and IF stage for the purpose of always maintaining good quality of received signal information by always optimizing analog baseband signal level to demodulator In addition, when the demodulation unit performs digital demodulation, the intermodulation interference level at a frequency where no multicarrier exists is detected and fed back to the AGC control loop of each stage as an AGC control signal. This is realized by performing AGC control to change the predetermined input value to the demodulator of the analog baseband signal so that the level becomes low.

  FIG. 1 is a block diagram showing a configuration example of a COFDM modulated signal receiver according to an embodiment of the present invention. However, the same parts as those in the conventional example will be described with the same reference numerals. The COFDM signal receiver includes a diplexer (distributor) 1, a combiner 2, a first tracking filter 3, a variable gain RF amplifier 4, a second tracking filter 5, a first mixer 6, and an RF stage local oscillator 7. , First buffer 8, second buffer 9, second PLL block 10, RF stage AGC block 11, first IF amplifier 12, first IF fixed bandpass filter 13, first IF amplifier 14, first low-pass filter 15, attenuator 16, second mixer 17, IF stage AGC block 18, RSSI block 19, crystal 20, third buffer 21, second IF amplifier 22, second IF fixed Bandpass filter 23, second IF amplifier 24, L-Band variable gain RF amplifier 25, L-Band mixer 26, L- and local oscillator 27, second low pass filter 28, third low pass filter 29, first PLL block 30, L-Band AGC block 31, IF local oscillator 32, first band pass filter 33, reference local oscillator 34, The antenna power supply terminal 35, DATA 36, CLOCK 37, LOCK 38, AFC control terminal 39, IF output terminal 40, fourth low-pass filter 41, RSSI output terminal 42, RF input terminal 45, demodulator 60, An AGC loop is provided in which an output of a detection value (for example, DAC output) in the DFT processing of the center frequency from the demodulator 60 is supplied to the L-Band variable gain RF amplifier 25, the variable gain RF amplifier 4, and the attenuator 16. Is different from the past. Further, the AGC control at each stage is configured so as to have a time constant in order from the subsequent stage from the viewpoint of reception sensitivity, in other words, maintaining a high C / N, and the amplifier (25, 4, 4) in the AGC loop of each stage. 16) In order to enable control from two signals, a signal obtained by analog detection (envelope detection) of the signal level of each stage and a signal output from the DAC after the DFT processing from the demodulator 60, The amplifying element is composed of, for example, a dual gate FET.

  Next, the operation of the present embodiment will be described. First, power induced in an antenna element (not shown) is taken in from an RF input terminal 45, and two bands of L-Band (1452 to 1492 MHz) and Band3 (175 to 240 or 250 MHz) used in the existing DAB are obtained by the duplexer 1. Extracted and sent to the L-Band gain variable RF amplifier 25 and the combiner 2, respectively. At this time, a DC current is supplied from the antenna DC supply terminal 35 to the antenna element via the low-pass filter 37.

  The signal sent to the L-Band gain variable RF amplifier 25 is amplified here, and then output from the L-Band local oscillator 27 controlled by the L-Band PLL block 30 in the L-Band mixer 26. To be an RF signal in the Band 3 frequency band, and further sent to the first tracking filter 3 via the combiner 2. On the other hand, the output signal from the L-Band mixer 26 is subjected to envelope detection by the AGC block 31, and the DC signal is input to one control terminal of the L-Band gain variable RF amplifier 25. At the same time, the detection value output 80 in the DFT processing from the demodulator 60 is input to the other control terminal of the L-Band gain variable RF amplifier 25. Therefore, the L-Band gain variable RF amplifier 25 sets the gain of the input RF signal in the Band 3 frequency band to a value determined by the envelope detection signal and the DFT processing detection value 80 and outputs it to the L-Band mixer 26. .

  After the Band 3 RF signal sent to the combiner 2 is sent to the first tracking filter 3 (many of which the single-tuning type is used) and subjected to band limitation, it is amplified by the Band 3 gain variable amplifier 4. The second tracking filter 5 is subjected to band limitation again and sent to the first mixer 6.

  The RF signal band-limited by the second tracking filter 5 is an RF stage local oscillator 7 whose oscillation frequency is controlled by the DC signal generated by the PLL block 10, the low pass filter 15, the RF stage local oscillator 7, and the buffer amplifier 9. Are mixed with the first output signal by the first mixer 6 and then sent to the first IF amplifier 12 as a first IF signal. The DC signal generated for controlling the oscillation frequency of the RF stage local oscillator 7 is also applied to the first tracking filter 3 and the second tracking filter 5 of the RF stage to control the center frequency of the pass band. To be used together.

  The signal down-converted to the first IF frequency by the first mixer 6 is amplified by the first IF amplifier 12 and then processed by the first IF fixed bandpass filter 13 at the RF stage. Compared with narrow band limitation. The first IF frequency signal subjected to the band limitation is amplified again by the second IF amplifier 14, passes through the attenuator 16, and is then sent to the second mixer 17.

On the other hand, the signal down-converted by the first mixer 6 is extracted by the RF stage AGC block 11 where it is subjected to envelope detection to become a DC signal, and this signal is one of the gain variable RF amplifiers 4. The detection value output 80 in the DFT processing from the demodulator 60 is input to the other control terminal. Therefore, the variable gain RF amplifier 4 sets the gain of the input RF signal to a value determined by the envelope detection signal and the DFT processing detection value 80 and outputs the value to the first mixer 6.

  Further, the second mixer 17 mixes the input RF signal and a fixed frequency signal generated by the combination of the crystal 20 and the local oscillator 32, thereby down-converting the signal by a certain frequency. 2 IF signal. The second IF signal is input to the IF stage AGC block 18, the RSSI block 19, and the second IF amplifier 22. The second IF signal is extracted by the IF stage AGC block 18 and subjected to envelope detection to become a DC signal, which is applied to one control terminal of the attenuator 16 and the other A detection value output 80 in DFT processing from the demodulator 60 is input to the control terminal. Therefore, the attenuator 16 attenuates the gain of the input first IF signal to a value determined by the envelope detection signal and the DFT processing detection value 80 and outputs the attenuated value to the second mixer 17.

  After the signal sent to the second IF amplifier 22 is amplified, it is subjected to the final narrowband restriction by the second IF fixed bandpass filter 23 in the next stage, and the second IF amplifier 24 demodulates the signal. Amplified to a signal level suitable for the input range of 60, and is sent to the demodulator 60 from the IF output terminal 40 as an analog baseband signal of the receiver.

  On the other hand, the second IF signal sent from the second mixer 17 is also applied to the RSSI block 19 and subjected to envelope detection with a small time constant, and then the high-frequency component is removed by the low-pass filter 41. Is output from the RSSI output terminal 42 to the demodulator 60 as an RSSI signal required by the subsequent demodulator 60 in the initial stage of synchronization.

  In the demodulator 60, the multi-carrier second IF signal transmitted from the IF output terminal 40 is converted into a digital signal by an AD converter, and then IQ demodulated (direct component demodulation), FFT (time axis-frequency expansion) In this case, the number of FET points is 2N (N is an integer) by performing DFT (Discrete Fourier Transform). The demodulator 60 performs FFT processing with the number of points equal to or greater than the number of multi-carriers of the OFDM modulated wave and 2N. The intermodulation distortion interference (IMD) level at the DFT point of the center frequency after the DFT processing in the demodulator 60 is used as the above-described DFT processing detection value 80, and the L-band gain variable RF amplifier 25, the gain variable RF amplifier 4, the attenuator. 16 will be fed back. It should be noted that the control method for each AGC loop by the feedback system from the demodulator 60 is adjusted by a time constant circuit (not shown) so that the AGC loops in the IF stage, the RF stage, and the Hi-BAND stage are in order. It shall be.

  By the feedback system from the demodulator 60 to each AGC loop, the analog baseband signal level sent from the IF output terminal 40 is set to the dynamic range in the AD converter (not shown) at the first stage of the demodulator 60. Control can be made to be always optimum, while deterioration of BER can be prevented by preventing intermodulation distortion interference from increasing. Conventionally, each AGC loop has worked so that the analog baseband signal level is constant with respect to the dynamic range of the AD converter regardless of the state of the received radio wave. However, in this embodiment, control by each AGC loop is performed. That is, the analog baseband signal level, which is the voltage target, is added so that the above-described intermodulation distortion interference is not increased by a feedback system from the demodulator 60 to each AGC loop.

  FIG. 2 is a diagram showing a waveform on the frequency axis of a signal subjected to COFDM modulation, and the above-described intermodulation distortion interference component in which the third and fifth orders are main components. The DFT point of Δf = 0 originally has no modulation signal component, but multicarriers arranged at equal frequency intervals generate distortion components due to intermodulation interference due to nonlinearity in the receiver. The same component is also generated at the upper and lower Δf step points outside the modulation band. In the figure, k is ½ of the number of multicarriers, and for example, in DAB mode I, k = 768 (* depending on standards such as DVB, IEEE802.11.a, or transmission MODEs therein). fsp is a multicarrier frequency step and is the reciprocal of the baud rate of each multicarrier in COFDM modulation. For example, in DAB mode I, fsp = 1 [kHz] (* DVB, IEEE802.11.a standard, or the like Depending on the transmission mode in the middle).

  Further, as the extensibility of the present embodiment, the number of DFT points is N to the power of 2, and the number of points is always set to exceed 2 × k, so that the upper and lower frequencies of Δf = fsp × k or more There is also a DFT calculation point in the band, and the detection level of this point detects not only intermodulation distortion but also the sum of ACS (adjacent channel leakage power). By further using this calculated value to generate a digital AGC control voltage from the demodulator 60, it is possible to realize AGC control that is more faithful to signal quality, such as when an undesired wave signal with a bad DU ratio exists in an adjacent channel. Is possible.

  The communication terminal with the external system controller has a bus (in this case, I2C bus: DATA36, CLOCK37, LOCK38) for controlling the N value of the PLL block 10 and recognizing the PLL lock, and the subsequent demodulator An AFC terminal 39 for fine frequency tuning from 60 is provided.

  According to the present embodiment, the DFT processing detection value (corresponding to the intermodulation distortion interference level) 80 from the demodulator 60 to the L-Band gain variable RF that constitutes each AGC loop of the Hi-BAND stage, the RF stage, and the IF stage. By adding AGC control according to the level of the intermodulation distortion component through a loop that feeds back to the amplifier 25, the variable gain RF amplifier 4, and the attenuator 16, an analog baseband signal corresponding to the dynamic range in the AD conversion unit that is the first stage of the demodulation unit 60 And the input level to the mixer at each stage can be kept optimal at all times, and therefore, BER device degradation, which is an indicator of the information quality of the received signal, can be greatly reduced.

  Also, a component block newly added to the hardware configuration of the demodulator 60 by using the DFT point detection level at Δf = 0 (center frequency), which is always processed during demodulation by the demodulator 60, for the AGC control. Therefore, the above effect can be obtained without impairing the downsizing of the apparatus or impairing the cost increase suppression.

  Further, since level detection is performed at a frequency equal to or higher than the sequential baud rate, it is possible to expect follow-up performance corresponding to mobile reception that is subjected to Rayleigh fading.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect.

It is the block diagram which showed the structural example of the COFDM modulation signal receiver which concerns on one embodiment of this invention. It is the figure which showed the waveform on the frequency axis | shaft of the signal by which COFDM was modulated, and the intermodulation distortion interference component which becomes the main as a 3rd order and 5th order component. It is the block diagram which showed the structural example of the tuner part of the receiver of DAB which is the conventional COFDM modulation system broadcast

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Diplexer (distributor), 2 ... Combiner, 3 ... 1st tracking filter, 4 ... Gain variable RF amplifier, 5 ... 2nd tracking filter, 6 ... 1st mixer, 7 ... RF stage local oscillator, 8 ... first buffer, 9 ... second buffer, 10 ... second PLL block, 11 ... RF stage AGC block, 12 ... first IF IF 1 IF amplifier, 13... First IF fixed bandpass filter, 14... 2 IF second IF amplifier, 15... 1st low-pass filter, 16... Attenuator, 17. , 18 ... IF stage AGC block, 19 ... RSSI block, 20 ... crystal, 21 ... third buffer, 22 ... first IF amplifier of second IF, 23 ... fixed band of second IF Pass-fill 24... 2nd IF second IF amplifier, 25... L-Band gain variable RF amplifier, 26... L-Band mixer, 27... L-Band local oscillator, 28. 29... Third low-pass filter, 30... First PLL block, 31... L-Band AGC block, 32... IF local oscillator, 33. 35 …… Antenna power supply terminal, 36 …… DATA, 37 …… CLOCK, 38 …… LOCK, 39 …… AFC control terminal, 40 …… IF output terminal, 41 …… fourth low-pass filter, 42 …… RSSI output Terminal 45... RF input terminal 60.

Claims (6)

When receiving the COFDM modulated wave of the desired channel and inputting it as an analog baseband signal to the demodulator, the AGC loop controlled by the analog detection signal of each stage of the Hi-BAND stage, the RF stage, and the IF stage is A COFDM modulated signal receiver that holds the analog baseband signal level input to the demodulator at a predetermined value by providing in a stage;
Detecting means for detecting an intermodulation interference level when the demodulator digitally demodulates the analog baseband signal level;
Feedback means for feeding back the detected intermodulation interference level to the AGC loop of each stage as an AGC control signal to vary the predetermined input value of the analog baseband signal to the demodulator;
A COFDM modulated signal receiver.   2. The COFDM modulated signal receiver according to claim 1, wherein the detecting means detects an intermodulation interference level at a DFT point of a center frequency after discrete Fourier transform (DFT) processing in the demodulator.   2. The COFDM modulation according to claim 1, wherein the feedback means applies the AGC control signal to the variable gain amplifying unit in order to adjust a gain of a variable gain amplifying unit constituting the AGC loop of each stage. Signal receiver.   4. The COFDM modulated signal receiver according to claim 3, wherein a dual gate FET is used as an amplifying element of the variable gain amplifying unit.   The AGC control signal by the feedback means is applied to the AGC loop of each stage through a time constant circuit, and a time difference is provided in the effect of the AGC control signal to the AGC loop of each stage. 5. The COFDM modulated signal receiver according to 4.   2. The COFDM modulated signal receiver according to claim 1, wherein the feedback means feeds back the AGC control signal to the AGC loop of each stage so that the intermodulation distortion component in the demodulator does not increase.

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