CN1708967A - Radio receiver and method for AM suppression and dc-offset removal - Google Patents
Radio receiver and method for AM suppression and dc-offset removal Download PDFInfo
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- CN1708967A CN1708967A CN 200380102037 CN200380102037A CN1708967A CN 1708967 A CN1708967 A CN 1708967A CN 200380102037 CN200380102037 CN 200380102037 CN 200380102037 A CN200380102037 A CN 200380102037A CN 1708967 A CN1708967 A CN 1708967A
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Abstract
A communications receiver includes a baseband signal recovery circuit (4) which uses a low-IF architecture for data reception. The baseband signal recovery circuit uses a full-analog implementation for channel selection and filtering (5). Thus, the overhead placed on the design of analog-to-digital converter is greatly relaxed and most of hardware can be re-used for multi- mode applications with only a slight modification.
Description
Technical field
The present invention relates generally to signal processing system, and more particularly, relate to the system and method that is used for recovering baseband signal at the receiver of communication system.
Background technology
Have little profile factor and can expect very much to be used in the modern wireless communication systems, and this be actual especially in cellular system with the design of the radio set of low cost manufacturing.Yet fully-integrated radio transceiver design is difficult to realize, because many cellular standards have strict performance requirement aspect sensitivity and the selectivity.
Directly conversion radio transceiver architecture is considered to be used to replace the ideal solution of widely used super-heterodyne architecture.The difficulty of design aspect is stricter than transmitter terminal at receiver end, because must satisfy selectivity and sensitivity requirement simultaneously in receiver.
Fig. 1 illustrates the superhet radio reception machine architecture of correlation technique, and Fig. 2 illustrates the direct conversion radio reception machine architecture of correlation technique.
A difference between these architectures is that super-heterodyne architecture is carried out channel selection and amplification at the IF of some appointments (intermediate frequency).Even form one or more foreign channels selective filters by ceramic filter or SAW filter usually, it is favourable carrying out at IF that channel selects aspect following at least.
At first, the DC skew is not a problem, because simple AC coupling can suppress to generate the DC skew and allow fast and stable (settling).Simultaneously, be minimized in the 1/f noise problem of finding in the direct conversion radio receiver of correlation technique, because carry out amplification in IF frequency away from DC.The second, by almost desirable passive filter, strong block signal (blocker) and adjacent channel signal are by most of filtering.Therefore, alleviated the consideration of relevant linearity.
Directly conversion radio reception machine architecture should solve and handle the problems referred to above of the prior art.Different with superheterodyne receiver, the DC skew is a problem in direct conversion receiver, therefore, should adopt suitable DC offset cancellation circuit.Even this DC offset removal circuitry works still has many shortcomings in real-world applications.
At first, the cut-off frequency of DC offset cancellation loop should be enough less than the desired signal bandwidth to reduce effect of inter-symbol.Usually, the cut-off frequency of DC offset cancellation loop is set to 1/1000 of channel width.Even proposed to implement with little chip size the technology of this DC servo loop, under the similar situation that is used in the very little channel width in GSM and the PDC communication network, the design of circuit parameter may be unrealistic.
In GSM standard, channel spacing is 200KHz and only is 25KHz in PDC.What is worse, when down-conversion was DC, the GSMK signal that is used in the GSM standard had most of signal energy at DC.Therefore, in GSM used, the DC skew was eliminated to become and more is difficult to carry out.The DC offset cancellation loop can suppress static DC skew, but when the dynamic DC of appearance is offset, has long transient process.Stabilization time and cut-off frequency are inversely proportional to, and are unacceptable thereby some are used.
Especially, for satisfying all requirements of GSM, radio receiver should be designed to suppress test by single-tone blocking test and AM.Although signal power is bigger under the situation of single tone blocker, the DC skew that the second-order distortion of block signal signal causes of improving oneself of built-in DC offset cancellation circuit filtering origin easily is because block signal is assumed that continuous sine wave signal.Yet, suppressing in the test at AM, block signal arrives the centre of grouping by force, and therefore filtering also is used to stablize by the DC skew that this block signal causes for a long time so apace.
Equally in GSM uses, because the transmission of packet-based signal adopts a DC skew to eliminate usually.In this case, if at digital baseband modulator-demodulator place, filtering DC skew inadequately, then the DC skew will reduce the signal to noise ratio of base band output.Modern GMSK demodulator comprises the high-performance analog to digital converter before Digital Signal Processing.Although in DSP, use to have the analog to digital converter of high dynamic range and other DC offset correction method can address this problem, still increased the weight of the design difficulty of analog to digital converter and the dynamic range that the DC skew should not exceed analog to digital converter.
Having proposed to solve a kind of method that DC offset problem and AM suppress is to use the analog to digital converter with high dynamic range and adopt the DC skew elimination algorithm that moves in digital signal processor.In this case, the amount of DC skew should be enough little, do not exceed the whole dynamic range of analog to digital converter.Typically, carrying out most of channel in baseband modem rather than in the analog component of receiver selects and gain controlling.Design challenge is present in the design of high-performance analog to digital converter.
The other method that has put forward to solve DC offset problem or second-order distortion is to use low-down IF architecture rather than direct conversion architecture.In low-down IF architecture, the DC skew that is caused by second-order distortion is positioned at outside the signal band, thereby is easy to be eliminated by digital filtering.By the filtering amount in the low IF receiver, alleviated requirement for the IIP2 of expression second-order distortion amount.Yet digital filtering also requires a plurality of position and because its high current drain and unacceptable in the analog to digital converter.Therefore, use digital low of radio receiver architecture to be limited to application such as GSM.
Comprise above-mentioned reference by reference at this, be suitable in addition or the suitable instruction of alternative details, feature and/or technical background.
Summary of the invention
The objective of the invention is to solve at least the problems referred to above and/or shortcoming and following advantage is provided at least.
The present invention is the receiver that comprises baseband signal recovery circuit, uses low IF architecture to be used for Data Receiving.This receiver preferably will be simulated entirely and be realized being used for channel selection and filtering.Therefore, alleviated the expense in the design of analog to digital converter widely, and most of hardware can both be used further to only have the multi-mode of slight modifications to use.The present invention is suitable for use in the application that requires high integrated radio receiver architecture.
In following specification, part is set forth additional advantage of the present invention, purpose and characteristic and check hereinafter or from the practice of the present invention, part will be conspicuous to those skilled in the art.As in claims, particularly pointing out, can realize and obtain objects and advantages of the present invention.
Description of drawings
To describe the present invention in detail with reference to following accompanying drawing, wherein, identical mark is represented components identical, wherein:
Fig. 1 is the block diagram that the superhet radio receiver of correlation technique is shown;
Fig. 2 is the block diagram that the direct conversion radio receiver of correlation technique is shown;
Fig. 3 is the block diagram according to the radio receiver of exemplary embodiment of the present invention;
Fig. 4 is the figure that illustrates according to the transfer function of the elliptic filter of exemplary embodiment of the present invention;
Fig. 5 is the figure that is illustrated in the waveform that the places at different levels of the radio receiver of realizing according to exemplary embodiment of the present invention produce;
Fig. 6 illustrates that be used for generating can be corresponding to the block diagram of the DDFS circuit of the oscillator signal of second local oscillator of the present invention (LO) signal; And
Fig. 7 illustrates that be used for generating can be corresponding to the block diagram of another circuit of the oscillator signal of second local oscillator of the present invention (LO).
Embodiment
Fig. 3 illustrates the baseband signal recovery circuit according to exemplary embodiment of the present invention.The direct conversion radio architecture that replaces correlation technique, the present invention uses low IF architecture to be used for Data Receiving.Yet different with other relevant technology systems, at least one embodiment of the present invention uses full simulation to realize being used for channel and selects and filtering.Therefore, be added in that expense in the design of analog to digital converter is alleviated widely and multi-mode that most of hardware can both be used further to only to have slight modifications is used.
As shown in Figure 3, use the orthogonal mixer that comprises frequency mixer 2 and 3, RF front end frequency mixer will down-convert to each intermediate frequency I and Q signal from the RF signal of LNA1.Orthogonal mixer should have the very phase place and the gain of coupling in i/q signal, be used for enough mirror images and suppress.Because the weak adjacent channel signal power in the GSM standard, required mirror image amount of suppression will be about 40dB.
After first down-conversion stage, can adopt optional gain stage and filtering stage to come part to suppress strong out of band signal and barrage noise and propagate into following level.
Second down-conversion mixer 4 will hang down the IF signal and down-convert to baseband signal.After carrying out this second down-conversion, can realize that also optional gain stage enters following level with barrage noise.Residue DC shifted signal or from the dynamic DC skew of second-order distortion induction through second frequency mixer, stand frequency translation, and this frequency becomes identical with the frequency of the 2nd LO signal.
After second down-conversion, be provided at the notch filter 5 that the frequency identical with the 2nd LO signal have dark depression and suppress the signal that this is not expected.Although the signal that can use low pass filter to suppress not expect, notch filter are more suitable for being offset the tone signal that causes in eliminating by static or dynamic DC.Can be that zero Chebyshev II mode filter is realized notch filter by elliptic filter and/or in some required frequencies.Different with the DC servo loop, the response time of current offset cancellation circuit is quite fast, because the DC skew is converted into high frequency rather than is positioned at DC.Therefore, aspect its absolute value and correction time, alleviated adverse effect widely from the DC skew.The design of the 2nd LO frequency in the present invention, and is extremely important aspect mirror image inhibition and AM inhibition ability.When the IF architecture was hanged down in use, because gain and unbalance in phase in a LO signal and the LO frequency mixer (2 among Fig. 3 and 3), some the signal leakage amounts from band internal congestion signal to required frequency band were inevitable.
For example, when in GSM uses, when the 2nd LO signal is 100KHz, desired signal will concentrate on 100KHz.The band internal congestion signal that is positioned at than the low 400KHz place of desired signal will have some image component at 300KHz.Owing to have at the band internal congestion signal of that frequency and to compare high amplitude with desired signal, suppress to be better than 36dB so that obtain required SNR from the mirror image of first frequency mixer more than 40dB.When the 2nd LO signal was shifted to higher frequency, because higher block signal level, the requirement that mirror image suppresses became stricter.Therefore, expect that the lowland is provided with the 2nd LO frequency so that alleviate the mirror image requirement of given first frequency mixer as far as possible.Yet the transient state of notch filter depends on the position of depression, and stabilization time and this frequency are inversely proportional to.The frequency translation that the DC that is caused by the strong block signal in the GSM application is offset through second frequency mixer (4 among Fig. 3) becomes carrier leak (carrier leakage).This carrier leak is proportional with the DC side-play amount and frequency is identical with the 2nd LO signal.Should eliminate this carrier leak apace to avoid causing error code in the demodulating process in baseband modem.Because under the help of notch filter, error code occurs under the situation that the transient time that the DC skew is eliminated is quite grown, the position of depression should be high as far as possible.When the requirement of considering the mirror image inhibition and transient response, determine that usually the 2nd LO frequency approaches 100KHz.
Fig. 4 is illustrated in the figure of an example that design attitude is the transfer function of zero elliptic filter.As shown in Figure 4, in filter transfer function, cause depression by zero.Null representation in the filter transfer function is in the gain of signal specific frequency, thereby can be suppressed fully.When considering the specific examples of GSM receiver, following calculating is for the requirement of second-order distortion.
Consider that the input block signal has-31dBm power in the frequency from desired signal skew 6MHz, and desired signal have be higher than sensitivity level 3dB-situation of 99dB.In order to keep the SNR of 9dB, the IIP2 of the input of LNA should be higher than
2x(-31)-(-99)+9＝46dBm (1)
The gain of supposing LAN is 15dB, and first down-conversion mixer should have the IIP2 performance that is better than 61dBm.Be not easy to realize this value by other circuit design techniques that use in the correlation technique.Yet, in the secondary down-conversion architecture of the embodiment that advocates of the present invention, suppose notch filter in zero position with signal suppressing 30dB, can make the IIP2 performance alleviate identical amount.Final IIP2 for frequency mixer requires to be about 16dBm, and this is easy to realize.
Fig. 5 is illustrated in each exemplary operation waveform according to the generations at different levels of the receiver of one exemplary embodiment of the present invention structure.As shown, when strong block signal arrives the input of LNA1, particularly in first down-conversion mixer, produce some DC side-play amounts.Even the low pass filter of the first down-conversion mixer back suppresses this block signal, owing to second-order distortion produces the DC skew.The IF signal is greater than signal bandwidth, so the DC skew is positioned at outside the desired signal itself.
After second down-conversion, desired signal with DC be the center and, DC skew becomes the tone signal at the 2nd LO frequency place.Notch filter is suppressed to this tone signal can be ignored or acceptable level.And after second down-conversion, optional gain stage and filtering stage suppress residual interference so that desired signal is provided and satisfies the signal strength signal intensity that is used for analog to digital converter.
In realizing exemplary embodiment of the present invention, best the 2nd LO signal be designed to have spectral purity (spectral purity) so that realize acceptable signal-to-interference ratio (SNR).The harmonic wave that should fully suppress the 2nd LO signal is not so that can be by harmonic mixing or parasitic mixing and produce serious interference.And preferably just in time the frequency with a LO signal is identical for the frequency of LO signal.
According to an exemplary embodiment, can use phase-locked loop (PLL) circuit to generate the LO signal.Yet under some environment, the frequency of the 2nd LO signal may be too low, and when this situation existed really, it was quite invalid to use PLL to be used for the 2nd LO generation.
Therefore, according to another exemplary embodiment, the present invention is with a kind of generation second local oscillator (LO) frequency in two kinds of methods.First method comprises uses Direct Digital Frequency Synthesizers (DDFS, Direct Digital Frequency Synthesizer) to be used to generate the 2nd LO signal.An example that is suitable for being used for DDFS technology of the present invention is disclosed at website www.analog.com.
Fig. 6 illustrates the general block diagram of the circuit of realizing the DDFS technology.In the figure, by reference clock incoming timing ROM table and DAC, and this circuit generates the pure single-tone that is used for the 2nd LO signal.According to the size of ROM and the position of DAC, the spectral purity in this example reaches and is lower than-90dBc.In Fig. 6, sine lookup table comprises the sinusoidal data that is used for number of cycles.Those skilled in the art will recognize and in look-up table, to use other surmount function data, and do not break away from the spirit and scope of the present invention.
Second method comprises the reference clock input used behind the frequency division and suppresses harmonic signal with filtering afterwards (postfiltering).Fig. 7 illustrates the exemplary circuit that generates the LO frequency signal based on this method.When realizing in GSM uses, for example, whole system uses 13MHz or 26MHz as the reference clock signal source from external crystal oscillator.When being removed 100 or 200 times, the 2nd LO signal becomes 130KHz.Remove 4 circuit in second frequency mixer, be provided for the accurate quadrature signals of one-sided down-conversion.In the end after the division level, eliminate a plurality of harmonic waves of clock signal by other filtering signal.
The present invention is better than relevant technology systems at least aspect following.Radio reception machine architecture of the present invention uses Analogical Circuit Technique to eliminate static DC skew and the dynamically DC skew that is caused by strong block signal.By using the mirror image inhibition structure and second frequency mixer with low-down frequencies operations, the system requirements of IIP2 is alleviated widely.Simultaneously, because because frequency inverted and convert DC skew to high-frequency signal, can at a good pace eliminate not matching or the result of the flip-flop of block signal level and any DC skew of generating as any kind.
Because no longer need be offset required little time constant in the elimination at the DC of other correlation techniques, it is also very fast to eliminate the required transient response of DC skew.Realize that by the simulation of using the radio receiver that suppresses the DC skew this radio reception machine architecture can be applied to be used for most of wireless applications, comprise the fully-integrated radio set that GSM uses.
In another exemplary embodiment of the present invention, radio receiving method comprises that the use first front end down-conversion mixer will down-convert to each intermediate frequency I and Q signal from the RF signal of first low noise amplifier (LNA).
In another exemplary embodiment of the present invention, a kind of radio receiving method comprises and uses down-conversion operation to obtain with DC as the desired signal at center and wherein that the DC skew becomes the tone signal of one of a plurality of local oscillators (LO) frequency.
From above-mentioned disclosure, other improvement of the present invention and variation will be apparent to one skilled in the art.Therefore, although only specifically described some embodiment of the present invention, can make various improvement obviously, and not deviate from the spirit and scope of the present invention at this.
The foregoing description and advantage only are exemplary and do not constitute restriction the present invention.This instruction can be applied to the device of other type easily.Description of the invention is intended that exemplary, and the scope that does not limit claim.Manyly substitute, improve and change apparent to one skilled in the art.In the claims, the statement of device+function intention is covered as structure described herein and carries out the function enumerated and not only structural equivalents but also equivalent structure.
Claims (24)
1. radio receiver comprises:
The first front end down-conversion mixer will down-convert to each intermediate frequency I and Q signal from the RF signal of first low noise amplifier (LNA).
2. radio receiver as claimed in claim 1, wherein, an orthogonal mixer is carried out the down-conversion of RF signal and phase place and the gain in the described frequency mixer coupling i/q signal.
3. radio receiver as claimed in claim 2, wherein, coupling phase place and gain are to realize the mirror image amount of suppression.
4. radio receiver as claimed in claim 1, wherein, described mirror image amount of suppression is about 40dB.
5. radio receiver as claimed in claim 1 wherein, uses gain stage and filtering stage to come part inhibition zone external signal and barrage noise to propagate into following stages.
6. radio receiver as claimed in claim 1, wherein, it is baseband signal that second down-conversion mixer will hang down the IF conversion of signals.
7. radio receiver as claimed in claim 6, wherein, the static or dynamically DC skew of described second frequency mixer conversion in frequency domain causes carrier leak, and described carrier leak is positioned at the same frequency of the 2nd LO frequency.
8. radio receiver as claimed in claim 6 wherein, uses gain stage to come barrage noise to be input to following stages.
9. radio receiver as claimed in claim 6 wherein, uses notch filter to eliminate the carrier leak that is caused by static or dynamic DC skew.
10. radio receiver as claimed in claim 8, wherein, described notch filter comprises at least one in elliptic filter and the Chebyshev II mode filter.
11. radio receiver as claimed in claim 1 wherein, uses phase-locked loop (PLL) circuit, generates a plurality of local oscillators (LO) signal that comprises a LO signal and the 2nd LO signal at least.
12. radio receiver as claimed in claim 10 wherein, uses Direct Digital Frequency Synthesizers (DDFS) to generate the 2nd LO signal.
13. radio receiver as claimed in claim 10, wherein, the reference clock input behind the use frequency division generates the 2nd LO signal, suppresses harmonic signal with filtering.
14. a radio receiving method comprises:
Use the first front end down-conversion mixer to down-convert to each intermediate frequency I and Q signal from the RF signal of first low noise amplifier (LNA).
15. radio receiving method as claimed in claim 13 wherein, uses gain stage and filtering stage to come part inhibition zone external signal and barrage noise to propagate in the following stages.
16. radio receiving method as claimed in claim 13, wherein, second down-conversion mixer will hang down the IF conversion of signals and become baseband signal.
17. radio receiving method as claimed in claim 13 wherein, uses gain stage to come barrage noise to be input in the following stages.
18. radio receiving method as claimed in claim 13 wherein, uses low IF architecture to receive data.
19. a radio receiving method comprises:
Use down-conversion operation to obtain as the desired signal at center and wherein, the carrier leak signal at DC skew becoming the 2nd LO frequency place with DC.
20. radio receiving method as claimed in claim 18 wherein, uses notch filter that carrier leak is suppressed to and can accept level.
21. radio receiving method as claimed in claim 18, wherein, the harmonic wave of the 2nd LO signal is designed to have spectral purity to realize accepting signal to noise ratio (SNR).
22. radio receiving method as claimed in claim 21, wherein, the frequency sum of a LO signal and the 2nd LO signal is identical with the required RF signal frequency from antenna.
23. radio receiving method as claimed in claim 21, wherein, the frequency of a LO signal is identical with the frequency of the 2nd LO signal.
24. radio receiving method as claimed in claim 23, wherein, a LO signal be near from the very high frequency of the input carrier signal of antenna and the 2nd LO signal near DC, and whole receiver architecture becomes low IF architecture.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US42105302P | 2002-10-25 | 2002-10-25 | |
| US60/421,053 | 2002-10-25 | ||
| US10/689,932 | 2003-10-22 |
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| CN1708967A true CN1708967A (en) | 2005-12-14 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN 200380102037 Pending CN1708967A (en) | 2002-10-25 | 2003-10-23 | Radio receiver and method for AM suppression and dc-offset removal |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101998459A (en) * | 2009-08-27 | 2011-03-30 | 中兴通讯股份有限公司 | Method and device for measuring single-tone field strength |
| CN102255626A (en) * | 2011-06-30 | 2011-11-23 | 清华大学 | Pi-network-based millimeter wave frequency band receiver with electrostatic discharge protection function |
| CN106130674A (en) * | 2016-06-12 | 2016-11-16 | 广州杰赛科技股份有限公司 | A kind of repeater band intercarrier leak suppressing method of testing and device |
| CN106209711A (en) * | 2015-02-06 | 2016-12-07 | 联发科技（新加坡）私人有限公司 | Multimode terminal receives device and DC offset concellation method thereof |
| CN107204790A (en) * | 2016-03-18 | 2017-09-26 | 三星电子株式会社 | Apparatus and method for providing the real-time second order input intercept point calibration of background |
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2003
- 2003-10-23 CN CN 200380102037 patent/CN1708967A/en active Pending
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101998459A (en) * | 2009-08-27 | 2011-03-30 | 中兴通讯股份有限公司 | Method and device for measuring single-tone field strength |
| CN101998459B (en) * | 2009-08-27 | 2013-03-27 | 中兴通讯股份有限公司 | Method and device for measuring single-tone field strength |
| CN102255626A (en) * | 2011-06-30 | 2011-11-23 | 清华大学 | Pi-network-based millimeter wave frequency band receiver with electrostatic discharge protection function |
| CN102255626B (en) * | 2011-06-30 | 2013-08-21 | 清华大学 | Pi-network-based millimeter wave frequency band receiver with electrostatic discharge protection function |
| CN106209711A (en) * | 2015-02-06 | 2016-12-07 | 联发科技（新加坡）私人有限公司 | Multimode terminal receives device and DC offset concellation method thereof |
| CN107204790A (en) * | 2016-03-18 | 2017-09-26 | 三星电子株式会社 | Apparatus and method for providing the real-time second order input intercept point calibration of background |
| CN107204790B (en) * | 2016-03-18 | 2021-03-02 | 三星电子株式会社 | Apparatus and method for providing background real-time second order input intercept point calibration |
| CN106130674A (en) * | 2016-06-12 | 2016-11-16 | 广州杰赛科技股份有限公司 | A kind of repeater band intercarrier leak suppressing method of testing and device |
| CN106130674B (en) * | 2016-06-12 | 2018-08-28 | 广州杰赛科技股份有限公司 | A kind of leakage of repeater in-band carrier inhibits test method and device |
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