CN1336721A - Method and device for detecting weak signal of known frequency - Google Patents
Method and device for detecting weak signal of known frequency Download PDFInfo
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- CN1336721A CN1336721A CN 00117306 CN00117306A CN1336721A CN 1336721 A CN1336721 A CN 1336721A CN 00117306 CN00117306 CN 00117306 CN 00117306 A CN00117306 A CN 00117306A CN 1336721 A CN1336721 A CN 1336721A
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Abstract
The method is to down conversion with local oscillator signal for weak signal to be detected with known frequency and another signal with same frequency to obtain two inter mediate frquency signals IF and LO, to do phase comparing for said two intermediate frequency signals to obtain two signals with amplitude A of detected signal, then to divide them into two parts, for each of then proceeded is: prime buffer amplifying, low-pass filtering and final buffer amplifying sequentially, then to be squared and operated, to do extracting for operated signal to obtain the detected signal, Said invention can perform detecting for weak signal in strong interference environment.
Description
The present invention relates to a kind of method and device that detects the small-signal of given frequency, particularly detect the method and the device of the amplitude of the pilot signal that has been attenuated at the final stage output of the feedforward linear power amplifier system that introduces pilot tone.
Development along with the global communication business, follow-on mobile communication base station system transmitter begins to adopt Linear Power Amplifier to export as final stage in a large number, feed-forward technique is the many methods that adopt in Linear Power Amplifier, eliminate the degree and the effect of nonlinear distortion in order to detect Feed Forward Power Amplifier, simultaneously feedforward loop circuit is controlled, generally adopt the method that increases pilot tone, seen Fig. 1.
But for communication system, the pilot signal that increases is a kind of interference signal to communication signal, therefore must it be reduced to below the level of communications protocol regulation at the output of transmitter, in gsm system, agreement is less than-36dBm to the requirement of this clutter interference, thing followed problem is: because the useful signal peak power output of transmitter is generally all more than 36dBm, will differentiate frequency detection system have the ability in strong " interference " that be higher than more than the detected signal 70dB, (refer to carrier wave, for pilot detection is to disturb, down with) detect the amplitude size of pilot signal in the environment, and detected pilot signal is flooded by noise usually, the frequency of " interference " signal, quantity is also uncertain, has brought difficulty with regard to the detection of giving pilot signal like this.
In order to address this problem, show that according to data that adopts at present has a following several method:
1) the pilot tone spread spectrum methods adopts pseudo random sequence code that pilot tone is carried out spread spectrum, makes it to be paved with whole working frequency range, with this pseudo random sequence code pilot tone is carried out despreading again at receiving terminal.Because Energy distribution is in whole frequency band behind the pilot tone spread spectrum, therefore less to the interference of any one carrier wave in this frequency range, the energy of pilot tone also is easy to detect after the despreading.See Fig. 2.
2) the outer method of band is placed on pilot tone outside the working frequency range, so amplitude can be bigger, is easy to detect.By behind power amplifier, adding filter pilot tone is filtered, see Fig. 3.
3) Super heterodyne is similar to traditional superheterodyne receiver, adopt frequency mixer that pilot tone is transformed to intermediate frequency, through filtering, in put the pilot signal frequency-selecting amplified, detect the amplitude of pilot tone at last with wave detector, the sensitivity of Super heterodyne can be done than higher, therefore pilot tone can be placed in the working band in this way, the cancellation level of pilot tone has reflected the cancellation level of whole working band intercarrier (the first loop LOOP1) or intermodulation (the second loop LOOP2) preferably.See Fig. 4.
Though above technology has advantage separately, they also have more fatal separately shortcoming, and the technical indicator that makes feedforward linear power amplifier is subjected to various restrictions and can not satisfies our requirement fully.
The benefit of pilot tone spread spectrum methods is the cancellation level that can reflect whole working band intercarrier (the first loop LOOP1) or intermodulation (the second loop LOOP2), but it has also added interference signal simultaneously in whole working band, all interference can be arranged to each carrier signal, might in communication, cause the high error rate.And navigation system constitutes complexity, cost height.
The advantage of the outer method of band is to be easy to detect, but require to add high performance filter, increased cost, also lossy to carrier wave simultaneously, another shortcoming of the outer method of band is to be in outside the working band because of pilot tone, just require the bandwidth of whole loop to increase, this is very difficult for parts such as main power amplifier, error power amplifier, if the bandwidth of loop can not be done wide or under wideband scenarios flatness poor slightly, pilot tone just can not correctly reflect the counteracting situation of loop, finally can cause the intermodulation index of Feed Forward Power Amplifier not meet the demands.See Fig. 5, this figure curve display the situation that offsets of loop, therefore the place offsets the degree maximum at the pilot tone point, departs from that pilot tone is far away more to be offseted poorly more, pilot tone is placed on that band is outer can not obtain the best effect that offsets in whole working band.
Though Super heterodyne has advantages such as sensitivity height, but its fatal weakness is a poor anti jamming capability, this is because intermediate-frequency filter can not be accomplished very narrow, squareness factor also has certain restriction, therefore when carrier wave will be during near pilot tone to pilot detection circuit generation serious disturbance, to such an extent as to make the circuit can't operate as normal.Unless the carrier wave of multicarrier transmitter be fix and enough frequency intervals are arranged, otherwise can not adopt this method.This is unpractical in the frequency hopping emission system that extensively adopts at present basically.
Purpose of the present invention is exactly in order to overcome the above problems, and a kind of method and device that detects the small-signal of given frequency is provided, so that can detect faint pilot signal under the strong jamming of carrier wave, antijamming capability is strong, and is highly sensitive.
The present invention realizes that the scheme of above-mentioned purpose comprises a kind of method and a kind of device that detects the small-signal of given frequency that detects the small-signal of given frequency.
The method of the small-signal of described detection given frequency comprises the steps:
Produce a local oscillation signal; To obtain the first intermediate-freuqncy signal IF after the small-signal of given frequency to be measured and the local oscillation signal down-conversion;
Obtain second intermediate-freuqncy signal LO with measured signal after with known signal of amplitude frequently and local oscillation signal down-conversion with one;
The above-mentioned first intermediate-freuqncy signal IF, the second intermediate-freuqncy signal LO are carried out the phase bit comparison, obtain two signal Asin θ, Acos θ that include the measured signal amplitude A, wherein θ is a phase difference;
Divide two-way with two signal Asin θ, Acos θ, the quadratic sum computing is carried out after carrying out the amplification of prime buffering, low-pass filtering, the amplification of final stage buffering successively in every road;
Signal after the computing is extracted square root.
The device of the small-signal of described detection given frequency comprises local oscillation signal generation device, down-conversion device, obtain the first intermediate-freuqncy signal IF after the local oscillation signal down-conversion that down-conversion device is used for the small-signal of given frequency to be measured and local oscillation signal generation device are produced, obtain the second intermediate-freuqncy signal LO with measured signal after with known signal of amplitude frequently and local oscillation signal down-conversion one; It is characterized in that: also comprise phase comparator, prime buffer amplifier, low pass filter, final stage buffer amplifier, quadratic sum circuit and extraction of square root circuit; An input of described phase comparator meets the above-mentioned first intermediate-freuqncy signal IF, and another input meets the above-mentioned second intermediate-freuqncy signal LO, and its output is two the signal Asin θ, the Acos θ that include the measured signal amplitude A, and wherein θ is a phase difference; Two signal Asin θ, Acos θ divide two-way, every road is behind prime buffer amplifier, low pass filter, final stage buffer amplifier, be connected to the input of quadratic sum circuit, the output signal of quadratic sum circuit is square A2 of the amplitude of measured signal, and this output signal connects the output of extraction of square root circuit.
The advantage of such scheme: owing to adopted technology such as coherent detection, low-pass filtering, quadratic sum, extraction of square root, it is strong therefore to have an antijamming capability, advantages such as sensitivity height.Not only be suitable for also can being used under other strong jamming occasions, detecting small-signal in that the faint carrier wave of detection under the strong carrier-in-interference is arranged.
Fig. 1 is a typical applications of the present invention---introduce the feedforward linear power amplifier system schematic of pilot tone.
Fig. 2 is a pilot tone spread spectrum methods schematic diagram.
Fig. 3 is the outer method schematic diagram of band.
Fig. 4 is the Super heterodyne schematic diagram.
What Fig. 5 was a Feed Forward Power Amplifier system intermediate ring road to pilot tone offsets the effect schematic diagram.
Fig. 6 is a principle of the invention block diagram.
Also the present invention is described in further detail in conjunction with the accompanying drawings below by specific embodiment.
The present invention can be used for multiple need be in strong interference environment to the place of its amplitude size of known Detection of Weak Signals, as communication, radar, detector etc.But this paper front is to being that example is carried out with dicyclo Feed Forward Power Amplifier system in the wireless communication system mainly in the description of background technology.For ease of describing, hereinafter still as example, but its practical occasion obviously is not to be confined to this.
Fig. 1 is a typical dicyclo feedforward linear power amplifier, and except that the pilot detection part, other parts are prior aries, and the present invention is exactly the improvement that the pilot detection part is made.Because amplifier nonlinearity, multi-carrier signal can produce harmful intermodulation component IMD (Intermodulation Distortion) through behind the amplifier.Main power amplifier (MPA) the 4th in last figure waits to improve linear amplifier, for the linearity of improving it need increase an error power amplifier (EPA) 13 and a main loop that is made of delayer 6,8, vector attenuator 3,12 that power ratio is less.Why being called the vector attenuator is because this attenuator both can change the amplitude of signal, can change the phase place of signal again.Can see that from the graph we are divided into three parts to feedforward system, loop 1 (LOOP1), loop 2 (LOOP2) and pilot detection, control section (coming out to automatic control section) from coupler 10,11.The function that loop 1 is realized mainly is to extract the intermodulation component IMD that signal produces by main power amplifier MPA, the function that loop 2 is realized is to amplify the intermodulation component IMD of extraction to offset the intermodulation component IMD in the carrier wave, make the signal of output comparatively pure, thereby improve the linearity of amplifier.
Wherein, pilot tone polit is by an independently phase-locked loop generation, be added to loop 1 and loop 2 in turn by single-pole double-throw switch (SPDT) K2, become the first pilot tone polit1 and the second pilot tone polit2 among the figure, and the narrowband pilot receiver (i.e. " polit detection " among the figure takes turns detection loop 1 and the loop 2 first pilot tone polit1 and the second pilot tone polit2 after offseting by single-pole double-throw switch (SPDT) K1, K1 and K2 take turns stream translation by the automatic control unit Synchronization Control between loop 1 and loop 2.
Said method need increase pilot tone in loop.As mentioned above, for communication system, the pilot signal that increases is a kind of interference signal to communication signal, therefore must it be reduced to below the level of communications protocol regulation at the output of transmitter, in gsm system, agreement is less than-36dBm to the requirement of this clutter interference, thing followed problem is: because the useful signal peak power output of transmitter is generally all more than 36dBm, will differentiate frequency detection system have the ability (to refer to carrier wave in strong " interference " that be higher than more than the detected signal 70dB, for pilot detection is to disturb, down with) detect the amplitude size of pilot signal in the environment, and detected pilot signal is flooded by noise usually, the frequency of " interference " signal, quantity is also uncertain, has brought difficulty with regard to the detection of giving pilot signal like this.The present invention just can address this problem.
Fig. 6 is a schematic diagram of the present invention.This figure had both illustrated device of the present invention, and method of the present invention also has been described.
Each square frame wherein is interpreted as a treatment step, and then this figure has illustrated a kind of method that detects the small-signal of given frequency, comprises the steps: to produce a local oscillation signal; To obtain the first intermediate-freuqncy signal IF after the small-signal of given frequency to be measured and the local oscillation signal down-conversion; Obtain second intermediate-freuqncy signal LO with measured signal after with known signal of amplitude frequently and local oscillation signal down-conversion with one; The above-mentioned first intermediate-freuqncy signal IF, the second intermediate-freuqncy signal LO are carried out the phase bit comparison, obtain two signal Asin θ, Acos θ that include the measured signal amplitude A, wherein θ is a phase difference; Divide two-way with two signal Asin θ, Acos θ, the quadratic sum computing is carried out after carrying out the amplification of prime buffering, low-pass filtering, the amplification of final stage buffering successively in every road; Signal after the computing is extracted square root.Carry out logarithmic detector at last, obtain signal A/D.
Each square frame wherein is interpreted as a processing unit, then this figure has illustrated a kind of device that detects the small-signal of given frequency, this device comprises that the local oscillation signal generation device (does not show among the figure, be embodied among signal LO and the IF, see Fig. 1), down-conversion device, obtain the first intermediate-freuqncy signal IF after the local oscillation signal down-conversion that down-conversion device is used for the small-signal of given frequency to be measured and local oscillation signal generation device are produced, obtain the second intermediate-freuqncy signal LO with measured signal after with known signal of amplitude frequently and local oscillation signal down-conversion one; It is characterized in that: also comprise phase comparator, prime buffer amplifier, low pass filter, final stage buffer amplifier, quadratic sum circuit and extraction of square root circuit; An input of described phase comparator meets the above-mentioned first intermediate-freuqncy signal IF, and another input meets the above-mentioned second intermediate-freuqncy signal LO, and its output is two the signal Asin θ, the Acos θ that include the measured signal amplitude A, and wherein θ is a phase difference; Two signal Asin θ, Acos θ divide two-way, and every road is connected to the input of quadratic sum circuit behind prime buffer amplifier, low pass filter, final stage buffer amplifier, and the output signal of quadratic sum circuit is square A of the amplitude of measured signal
2, this output signal connects the output of extraction of square root circuit.
Among Fig. 6, IF is pilot tone (the second pilot tone polit2 of first pilot tone polit1 of process loop 1 or process loop 2 through loop, relevant with the state of K switch 1, K2) with the local oscillator down-conversion after the intermediate-freuqncy signal that obtains, it has comprised the amplitude information A that represents the degree that offsets, and phase place is different and different to the control of vector attenuator with loop.LO be pilot tone directly with the local oscillation signal down-conversion after the signal that obtains, it and the same frequency of intermediate-freuqncy signal, the phase place relative fixed, comparing phase place with IF has difference.A/D is the final output of coherent detection, gives the foundation of automatic control circuit as control vector attenuator.Wherein local oscillation signal be by one independently the local oscillation signal generation device produced, its frequency and pilot signal differ IF.
The coherent detection circuit can be divided into following several functional module according to function:
Phase comparator, buffering amplification, low pass filter, quadratic sum, extraction of square root and direct current logarithmic detector illustrate the function of each module below respectively.
Phase comparator as shown in Figure 6, the intermediate-freuqncy signal of putting in local oscillator and the process enters phase comparator, because two signals are with frequently, has only the phase place difference, therefore this phase comparator is output as two direct current signals representing ASin θ and ACos θ respectively, has wherein comprised the phase information θ of the amplitude information A of pilot signal and local oscillator, intermediate frequency.
Class buffer amplifier has all added buffer amplifier circuit before and after low pass filter, its objective is to play the requirement of isolating and satisfying gain.
Low pass filter because of interference signal and local oscillation signal altogether irrelevant, therefore interference signal is output as an AC signal with local oscillator than producing mutually after entering into phase comparator, interference signal and pilot signal are leaned on closely more, the AC signal frequency that produces is low more, this interference signal is superimposed upon pilot signal than on the direct current signal that the back produces mutually, in order to remove these interference signals, need the low pass filter that cut-off frequency is very low, so that the alternating current component that interference signal is produced filters.The key of this circuit antijamming capability just is this low pass filter, adopts special-purpose switching capacity low pass filter chip can accomplish the low pass filter that cut-off frequency is very low at an easy rate.Most of interference signal can be filtered by this filter, guarantee the accuracy of coherent detection.
Quadratic sum circuit and extraction of square root circuit will be sued for peace through behind the ASin θ of low-pass filtering and the ACos θ signal square, according to following formula:
(ASinθ)
2＋(ACosθ)
2＝A
2
Removed phase component wherein, extraction of square root can obtain range weight A again, the component that detection method of the present invention that Here it is and device detect.On behalf of loop, this range weight A offset the size of the remaining weight of pilot frequency in back.Also just represented the degree of offseting.Remaining weight of pilot frequency is more little, and it is good more to offset.
Though the signal that process quadratic sum circuit obtains also can represent to remain the amplitude of pilot signal, but because the excursion of A is greater than 35dB, dynamic range can be bigger after square, makes troubles for the detection of back, therefore need to its extraction of square root the function of Here it is extraction of square root circuit.
It is the component of a linear change that the direct current logarithm detects the amplitude information A that obtains after the extraction of square root, and when the value of A was very little, the variable quantity of its every 1dB has only several millivolts, and was just very high for the requirement of A/D sampling like this.For reducing the difficulty of A/D sampling, after being taken the logarithm, A obtains variable with the decibels variation, and the variable quantity of A in whole dynamic range is exactly uniform like this, detects the dynamic range that has guaranteed coherent detection by the direct current logarithm.
Advantages such as according to the description of above each functional module, this characteristic feature of an invention is to have adopted technology such as coherent detection, low-pass filtering, quadratic sum, extraction of square root and the detection of direct current logarithm as can be seen, and it is strong, highly sensitive therefore to have an antijamming capability, and dynamic range is big.In actual use, for further strengthening antijamming capability, can also add frequency modulation(FM), phase modulated etc. respectively or simultaneously to pilot tone, local oscillator.Because of detected intermediate frequency pilot signal all is to be got by identical frequency source with intermediate frequency local oscillator signal for referencial use, so the frequency drift of frequency source do not constitute influence to detecting, and reduced the requirement of frequency source.
The present invention compared with prior art benefit of maximum is can not produce any interference to carrier wave, and And it is simple to implement circuit, and cost is low.
Claims (6)
1, a kind of method that detects the small-signal of given frequency comprises the steps:
Produce a local oscillation signal;
To obtain the first intermediate-freuqncy signal IF after the small-signal of given frequency to be measured and the local oscillation signal down-conversion;
Obtain second intermediate-freuqncy signal LO with measured signal after with known signal of amplitude frequently and local oscillation signal down-conversion with one;
The above-mentioned first intermediate-freuqncy signal IF, the second intermediate-freuqncy signal LO are carried out the phase bit comparison, obtain two signal Asin θ, Acos θ that include the measured signal amplitude A, wherein θ is a phase difference;
Divide two-way with two signal Asin θ, Acos θ, the quadratic sum computing is carried out after carrying out the amplification of prime buffering, low-pass filtering, the amplification of final stage buffering successively in every road;
Signal after the computing is extracted square root.
2, the method for the small-signal of detection given frequency as claimed in claim 1 is characterized in that after extraction of square root, also signal is carried out logarithmic detector.
3, the method for the small-signal of detection given frequency as claimed in claim 1 and device is characterized in that: earlier signal is carried out frequency modulation(FM) or phase modulated before detection.
4, a kind of device that detects the small-signal of given frequency, comprise local oscillation signal generation device, down-conversion device, obtain the first intermediate-freuqncy signal IF after the local oscillation signal down-conversion that down-conversion device is used for the small-signal of given frequency to be measured and local oscillation signal generation device are produced, obtain the second intermediate-freuqncy signal LO with measured signal after with known signal of amplitude frequently and local oscillation signal down-conversion one; It is characterized in that: also comprise phase comparator, prime buffer amplifier, low pass filter, final stage buffer amplifier, quadratic sum circuit and extraction of square root circuit; An input of described phase comparator meets the above-mentioned first intermediate-freuqncy signal IF, and another input meets the above-mentioned second intermediate-freuqncy signal LO, and its output is two the signal Asin θ, the Acos θ that include the measured signal amplitude A, and wherein θ is a phase difference; Two signal Asin θ, Acos θ divide two-way, and every road is connected to the input of quadratic sum circuit behind prime buffer amplifier, low pass filter, final stage buffer amplifier, and the output signal of quadratic sum circuit is square A of the amplitude of measured signal
2, this output signal connects the output of extraction of square root circuit.
5, the device of the small-signal of detection given frequency as claimed in claim 4 is characterized in that: also comprise the logarithmic detector circuit, the output of its input termination extraction of square root circuit.
6, as the device of the small-signal of claim 4 or 5 described detection given frequencies, it is characterized in that: also comprise frequency modulation circuit or phase-modulation circuit, be positioned at before the phase comparator.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB001173065A CN1192492C (en) | 2000-07-28 | 2000-07-28 | Method and device for detecting weak signal of known frequency |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB001173065A CN1192492C (en) | 2000-07-28 | 2000-07-28 | Method and device for detecting weak signal of known frequency |
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| Publication Number | Publication Date |
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| CN1336721A true CN1336721A (en) | 2002-02-20 |
| CN1192492C CN1192492C (en) | 2005-03-09 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNB001173065A Expired - Lifetime CN1192492C (en) | 2000-07-28 | 2000-07-28 | Method and device for detecting weak signal of known frequency |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101145860A (en) * | 2007-07-06 | 2008-03-19 | 哈尔滨工程大学 | Device for real time correction of channel phase amplitude |
| CN114337707A (en) * | 2021-12-20 | 2022-04-12 | 中国船舶重工集团公司第七二三研究所 | Harmonic/intermodulation signal judgment circuit and method of superheterodyne receiver |
-
2000
- 2000-07-28 CN CNB001173065A patent/CN1192492C/en not_active Expired - Lifetime
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101145860A (en) * | 2007-07-06 | 2008-03-19 | 哈尔滨工程大学 | Device for real time correction of channel phase amplitude |
| CN101145860B (en) * | 2007-07-06 | 2010-09-08 | 哈尔滨工程大学 | Device for real time correction of channel phase amplitude |
| CN114337707A (en) * | 2021-12-20 | 2022-04-12 | 中国船舶重工集团公司第七二三研究所 | Harmonic/intermodulation signal judgment circuit and method of superheterodyne receiver |
| CN114337707B (en) * | 2021-12-20 | 2023-10-13 | 中国船舶重工集团公司第七二三研究所 | Harmonic/intermodulation signal judging circuit and method of superheterodyne receiver |
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| Publication number | Publication date |
|---|---|
| CN1192492C (en) | 2005-03-09 |
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