RF project often is regarded as the black blackart of electronic domain. It may be maths and some kind of mechanical peculiar combination, it is trial and error merely even sometimes. It lets a lot of outstanding engineers do not get its to solve, some engineers know an outcome only and be without place to know to detail. A lot of existing document often do not build basic idea, hop to explain to theory and maths directly however.

 

Plural RF first detector uncovers secret

 

Graph 1 it is to use go up transducer (catapult) the graph of principle of plural first detector of configuration. Two collateral method have independent first detector each, communal this brace up to these method feed signal, this brace up rather in of a first detector phasic differ 90° . Two independent output are subsequently in amplifier of sue for peace sue for peace, generate needs RF output.

 

Graph 1. Plural catapult is basic framework

 

This configuration has a few simple but very useful application. Go up in I input only suppose feed sound of a signal, and not drive Q input, if pursue,2 are shown. Assume I inputs the signal sound frequency that go up to be X MHz, criterion the output of the ±x of frequency of LO of first detector generation in I method. Because do not have signal to bring to bear on to be inputted at Q, the spectrum that the first detector in this method produces is empty, the output of I first detector becomes RF output directly.

 

Graph 2. I method is analysed

 

Or, bring to bear on to Q input only suppose the signal sound that a frequency is X. Q first detector produces signal sound to be the output of LO frequency ±x then. Because do not have signal to bring to bear on to be inputted at I, its first detector outputs Jing Yin, the output of Q first detector becomes RF output directly.

 

Graph 3. Q method is analysed

 

Look suddenly, graph 2 with the graph the output of 3 appears identical. But actually, both has a crucial difference, that is phasic. Bring to bear on identical signal sound to be inputted at I and Q at the same time suppose, and 90° phase shift exists between input passageway, if pursue,4 are shown.

 

Graph 4. The method that I and Q signal bring to bear on in the meantime is analysed

 

Examine first detector output carefully, we observe: It is inphase that LO frequency adds the signal that inputs frequency, but LO frequency decreases the signal that inputs frequency is surprise appearance. This brings about the signal sound addition of LO upside, and the disappear of signal sound photograph of underside. Without any filter wave, we were eliminated among them sound of a signal (or webbing) , the output of generation is located in a side of LO frequency completely.

 

In the graph 4 show case in, I signal compares 90° of Q signal lead. If change configuration to make,Q signal compares 90° of I signal lead, can anticipate so can have similar addition and photograph pass the time in a leisurely way, but fall in this kind of circumstance, all signal will appear in the underside of LO.

 

Graph 5. Signal phoneme buy depends on the phasic relation of I and Q

 

The graph above the 5 labs that showed a plural catapult measure an outcome. What left shows is the test case of 90° of lead of I comparing Q, its bring about output signal sound to be located in the upside of LO. Graph 5 right showed contrary concern, namely 90° of lead of Q comparing I, the output signal news that gets from this is located in LO underside.

 

Theoretic ought to a side that can allow full capabilities to fall in LO only. However, if pursue,5 medium labs measure result place to show, disappear of complete in practice photograph is impossible to happen, a few energy can stay in the other a side of LO, this is alleged mirror. Still should notice, the energy of LO frequency also is existence, call LO leak or LOL. Other energy — still can see in the result these are the harmonic that need signal, the article does not give discuss.

 

To eliminate a mirror completely, I and the extent that Q first detector outputs must agree completely, and go up in LO mirror side between each other phasic and apropos differ 180° . If cannot be satisfied afore-mentioned phasic ask with extent, so the addition that the graph shows 4 times / photograph disappear process is met not quite ideal, the energy of mirror frequency still can exist.

 

Influence

When using framework of groovy odd first detector, produce LO± product. Before blasting off, need is eliminated among them a webbing, it is normally take a filter to eliminate through increasing. Of filter boil fall frequency must proper, make its can eliminate the mirror signal that does not need already, won’t affect the signal of need again.

 

Graph 6. Filter of mirror of odd first detector asks

 

Mirror and place need the removed meeting between signal to affect the demand to filter directly. If interval is bigger, can use boil fall relatively the filter of simple low cost of delay. If interval is narrower, the design must come true have abrupt response filter, use multipolar dot or SAW filter normally. Because this can say, mirror and place need the interval that must keep proper between signal, so that filter divides a mirror and can not affect place to need signal; Of this interval and filter complex spend and cost becomes inverse ratio. In addition, if LO frequency is alterable, filter must adjustable humorous, what this meeting increases filter further is complex degree.

 

Mirror and place need the interval between signal by bring to bear on to decide at the signal of first detector. Graph 6 medium example show a 10MHz bandwidth with DC apart 10 MHz signal. Corresponding first detector outputs the place that wants mirror park and place signal apart 20MHz. In this kind of configuration, need signal spectrum to the place that realizes 10MHz is carried in output, must let method of signal of base band of a 20MHz join first detector. The base band bandwidth of 10MHz was not used, the prep above of data interface rate of first detector circuit is necessary level.

 

Return the plural first detector that the graph shows 5 times, we know our the framework eliminated a mirror and need not exterior filter wave. And, efficiency can be optimized in framework of 0 intermediate frequency, make bandwidth of signal method processing is equal to place to require signal bandwidth. The notional picture that the graph shows 7 times explained its realize a principle. As above, if I compares Q lead 90° , criterion only LO upside can have output. If Q compares I lead 90° , criterion only LO underside can have output.

 

Accordingly, if generate signal of two independent base band, among them a design is become only output of the webbing on generation, another design is become produce below to take another design to become only produce next webbing to output only, so OK in base band lieutenant general its addition brings to bear on Yu Fu counts catapult. The result will be to have the output of different signal to appear in LO upside and underside. In applying actually, signal of assorted base band arises with digital means. The graph shows node of sue for peace 7 times is to show this idea only.

 

Graph 7. Framework of first detector of complex number of 0 intermediate frequency

 

Bonus of 0 intermediate frequency

Use plural catapult to produce unilateral to take output to have quite big gain, can reduce the RF filter wave that needs to eliminate mirror place. However, if property of mirror photograph disappear is enough good, make the mirror can be ignorred, can use mode of 0 intermediate frequency to produce the advantage of this framework further so. 0 intermediate frequency allow us to use special the base band data that found will generate RF output, be in thereby the signal that two side of LO appear to become independent each other. Graph 8 showed this is how to come true. We have the I of two groups of mutual independence and Q data, with symbolic data encode, receiver is OK according to fiducial carrier wave phasic undertake decipher.

 

Graph 8. The I/Q signal in inspecting first detector of complex number of 0 intermediate frequency to configure deep

 

Initiative observation shows: Q1 compares I1 lead 90° , the extent of both is consistent. Similar, i2 compares Q2 lead 90° , its extent is likewise consistent. Incorporate these independent signal, make I1 + I2 = SumI1I2, q1 + Q2 = SumQ1Q2. The I after addition and Q signal are shown no longer phasic with extent dependency — its extent is in all moment are unequal, the phasic relation between both changes ceaselessly. The first detector of earning outputs a side carrier wave of I1/Q1 data park, the other a side of carrier wave of I2/Q2 data park, reach a figure as above 7 are shown.

 

Pass the independence adjacent of each other photograph the either side of LO of data piece park, 0 intermediate frequency make the advantage of plural catapult gets strengthening. Bandwidth of data processing method won’t exceed data bandwidth absolutely. Accordingly, theoretic, plural first detector was used to offer a kind of solution in framework of 0 intermediate frequency, its do not need RF filter wave, still can optimize efficiency of base band power at the same time, reduce the unit cost that cannot use signal bandwidth.

 

So far, the key of the article is plural first detector uses as catapult of 0 intermediate frequency. Same principle also holds water conversely, namely framework of plural first detector can use as receiver of 0 intermediate frequency. The advantage that shows in the light of catapult applies to receiver likewise. When using odd first detector to receive signal, must use RF first detector filter to divide mirror frequency above all. In 0 intermediate frequency working mode falls, need not worry about mirror frequency, the signal of prep above LO receives be being received with the signal under LO is mutual independence.

 

Following plan institute show plural receiver. Input spectrum brings to bear on to be mixed at I at the same time Q first detector. A first detector adopts LO drive, another first detector adopts drive of LO + 90° . The output of receiver is I and Q. To receiver, how will the output that wants to be proved to give input correspondence by experience not allow easy, but if input LO of signal sound prep above, if plan institute is shown, so I and Q output will are in (signal sound–LO) frequency, and I is mixed can be phase shift between Q (lead of I comparing Q) . Similar, if input signal sound under LO, so I and Q output are to be in likewise (LO–Signal sound) frequency, but it is lead of Q comparing I at this moment. Carry this kind of kind, plural receiver can distinguish the energy of prep above LO and the energy under LO.

 

The output of plural receiver will be the sum of information of two kinds of I/Q: A kind of delegate receives the spectrum of reception prep above LO, another kind of delegate receives the reception spectrum under LO. This one concept already was aimed at plural catapult to had done a specification in front, it is the Q after the I signal after addition and addition signal brings to bear on among them Yu Fu counts catapult. To plural receiver, the base band processor of the Q information after the I information after receiving addition and addition can use plural FFT to distinguish easily more high frequency rate and inferior frequency.

 

Graph 9. First detector receiver configures complex number of 0 intermediate frequency

 

When the Q signal after the I signal after receiving addition and addition, the Q signal —— after the I signal after having addition of —— of two known quantities and addition but have 4 unknown quantity, namely I1, Q1, I2 and Q2. As a result of unknown quantity over known quantity, because this cannot solve an I1, Q1, I2 and Q2 it seems that. However, we still know I1 = Q1 + 90, i2 = Q2–90, after having these two foregone concerns, the Q signal solution after the I signal after can using received addition and addition gives I1, Q1, I2 and Q2. In fact, we need to solve an I1 and I2 only, because Q signal is the carbon of I signal, ±90 of phasic nevertheless deflection just.

 

Limitation

In practice, plural first detector tries to eliminate mirror signal completely. This one limitation has two outstanding effects to radio framework design.

 

Although function is restricted, answer intermediate frequency still can bring cogent profit. Try the case of low intermediate frequency that consideration graph shows 10 times. Because function is restricted, we can see a mirror really. However, the anticipation that designs to odd first detector together is compared (refer to a graph 6) , this mirror already greatly damply. Although plural first detector still needs filter, but can loosen to the requirement of this filter a lot of, its implementation is simpler also, cost is inferior.

 

Graph 10. The actual implementation of plural first detector notices the mirror of attenuation.

 

Filter is complex degree need the distance between signal to become inverse ratio with mirror and place. If use configuration of 0 intermediate frequency, this distance will turn into 0, the mirror is located in place to require signal frequency paragraph in. The actual application of theory of 0 intermediate frequency cannot come true completely, the mirror inside the belt of generation brings about function to reduce not acceptable level (refer to a graph 11) .

 

Graph 11. The limitation that 0 intermediate frequency realize

 

What satisfy method of I and Q data only is phasic ask with extent, the principle of plural catapult and receiver just holds water. Of signal method do not match the mirror signal that can bring about two side of LO cannot accurate photograph disappear. The example of this kind of problem refers to a graph 10 with the graph 11. Below the case that does not use 0 intermediate frequency, can use filter wave to eliminate a mirror. However, if use framework of 0 intermediate frequency, the mirror that does not need can fall inside the spectrum range that needs signal directly, if mirror power is enough big, can malfunction state. Accordingly, what only the design can eliminate signal method go up is phasic and when extent is abhorrent, use 0 intermediate frequency and plural mixing ability to offer best system to devise plan.

 

Advanced algorithm supports

The concept of framework of plural first detector already existed a lot of years, but contented in dynamic radio environment phasic the use that restricted its to fall in mode of 0 intermediate frequency with the challenge that extent asks. ADI uses design of intelligent silicon chip and advanced algorithm integratedly, overcame these challenges. The design allows existence to affect the factor of signal method, but design of intelligent silicon chip falls these influences to lowest. The error that leave is passed optimize orthogonal error correction oneself (QEC) algorithm is eliminated. Graph 12 it is notional graph.

 

Graph 12. Advanced QEC algorithm and design of intelligent silicon chip support framework of 0 intermediate frequency

 

Send and receive in the ADI such as AD9371 implement on, QEC algorithm is located in piece inside in ARM® processor. The RF output that it masters modulation of method of silicon chip signal, classics continuously, information that inputs signal and outside system environment, use this information to get used to signal method outline with forecasting means intelligence controlledly, is not to make natural type passivity react. This algorithm performance is excellent, can regard its as with digital means method of auxiliary imitate signal develops optimum behavior.

 

ADI is sent and receive implement interior has a variety of advanced algorithm to be stationed in stay and produce effect, algorithm of dynamic QEC calibration is only among them a more outstanding example. Other the algorithm that coexists to it still has LO leak to eliminate etc, these algorithm promote best standard the property of framework of 0 intermediate frequency. This kind of generation is sent and receive implement algorithm basically is used at support to implement relevant technology, and the 2nd generation is algorithmic (word of example exactly the number beforehand lack fidelity or DPD) can increase not only send and receive implement function, return the property that can promote whole system.

 

All systems have the place of a few inadequacy to be able to limit its function. generation algorithm is main focusing is eliminated at passing calibration piece inside limitation, and new generation algorithm uses intelligent means to eliminate send and receive implement external systematic performance and efficiency limitation element, for example PA is lack fidelity with efficiency (DPD and CFR) , diplexer function (the TxNc) , passive problem that make shift (PIM) .

 

Epilogue

Plural first detector already existed a lot of years, dan Jijing resembles restraining function not to allow to use its at mode of 0 intermediate frequency. Design of intelligent silicon chip and advanced and algorithmic union removed the function obstacle that prevents high-powered system formerly to use framework of 0 intermediate frequency. After function limitation is eliminated, use framework of 0 intermediate frequency complex to reducing filter wave, power comsumption, system degree, dimension, quantity of heat and weight have profit.

 

Mix to plural first detector 0 intermediate frequency, we can consider to use QEC and LOL algorithm as supportive function. But, what develop range as algorithm is patulous, it designed personnel to bring higher performance level to the system, make them can more agile the ground designs radio. They can choose the performance that enhance already, the help that also can use algorithm to offer will reduce the cost that radio designs or size of parts of an apparatus.

 (origin: Yadenuo semiconductor)