CN102628897A - Based on N1dB compression point and N2Three-order intermodulation test method of dB compression point - Google Patents

Abstract

The invention relates to the technical field of nonlinear parameter testing of amplifiers, and discloses a non-linear parameter testing method based on N₁dB compression point and N₂The third-order intermodulation test method of the dB compression point comprises the following steps: sequentially connecting a signal source, an amplifier to be tested and a power meter; a signal source inputs power to an amplifier to be tested, the input power is gradually increased, and a power meter measures output power corresponding to each input power; determining N from the measured input and output powers₁dB compression point input power sum N₂dB compression point input power; from N₁dB compression point input power sum N₂Calculating the difference value delta of the input power of the dB compression point; substituting the difference value delta into a third-order intermodulation calculation formula to calculate N₁Power difference delta between input power of dB compression point and input power of third-order intermodulation point_IIP3(ii) a And the power difference value delta_IIP3And correcting to obtain the input power value of the third-order intermodulation point. The invention reduces the cost of the test system, simplifies the test structure, and can ensure high precision by adding correction value correction after the calculation of the algorithm.

Description

Based on N 1DB compression point and N 2The third order intermodulation method of testing of dB compression point

Technical field

The present invention relates to amplifier nonlinearity parameter testing technical field, relate in particular to a kind of based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point is used to realize the calculating of third order intermodulation point power input (IIP3) value.

Background technology

Common test for amplifier generally comprises three aspects: linear test, non-linear test, noise figure test; Wherein the parameter that relates to of non-linear test mainly comprises 1dB compression point and third order intermodulation point (IP3), especially more can embody the amplifier nonlinearity characteristic with third order intermodulation point.In radio frequency or microwave multicarrier communication system; The third order intermodulation point is an important indicator of weighing the linearity or distortion; It includes third order intermodulation point power input (IIP3) and these two parameters of third order intermodulation point output power (OIP3), and third order intermodulation method of testing provided by the invention mainly is in order to realize the calculating to third order intermodulation point power input value.

Crosstalk can produce crosstalking of adjacent channel, concerning digital microwave telecommunication concerning simulated microwave communication; The availability of frequency spectrum of meeting reduction system; And the bit error rate is worsened, so the big more system of capacity, require third order intermodulation point high more; Be that third order intermodulation point power input is big more, this representes that also the linearity is good more few more with distortion.

The method of testing of third order intermodulation point is normally tested the contiguous signal of two frequencies of input in the prior art; When in the contiguous signal of these two frequencies drops on the bandwidth of amplifier and through non-linear amplification region, amplifying; Its output signal will comprise the various multistage frequency components that produced by the contiguous signal of these two frequencies; Third order intermodulation component 2F1-F2 and 2F2-F1 are that three rank in the non-linear frequency (being the cube item) produce in these multistage frequency components; Because it often is in the bandwidth of amplifier, therefore be to need the main nonlinear component of paying close attention to, see Fig. 1.

Fig. 2 has reflected the gain trace of fundamental frequency (single order intermodulation) with third order intermodulation, and when power input was increased to input third order intermodulation point (IIP3) gradually, fundamental frequency and third order intermodulation gain trace intersected, and corresponding output power is output third order intermodulation point (OIP3).IIP3 and OIP3 are defined as input third order intermodulation point and output third order intermodulation point respectively, are the horizontal ordinate parameter of IP3, realize the third order intermodulation test thus.

The third order intermodulation method of testing mainly comprises following step in the prior art: step 1: connect equipment according to Fig. 3 test block; Step 2: export one tunnel radiofrequency signal F1; Step 3: export another road radiofrequency signal F2; Step 4: open spectrum analyzer; Step 5: open tested amplifier; Step 6: on spectrum analyzer, read the output power of F1 or F2, this is the value of a point (like Fig. 2); Step 7: on spectrum analyzer, read the output power of 2F1-F2 or 2F2-F1, this is the value of b point (like Fig. 2); Step 8: calculate output third order intermodulation point OIP3 and input third order intermodulation point IIP3:

${\mathrm{OIP}}_3=a+\frac{a-b}{2}=\frac{3a-b}{2}$

IIP ₃＝OIP ₃-G

Wherein, G is an Amplifier Gain.

But; Have following defective in the third order intermodulation test in the prior art: at first, the signal power that outputs to spectrum analyzer can not be too high, avoids the nonlinear distortion that is produced by spectrum analyzer; This is required the output power of radio-frequency signal source little; And can find out that by Fig. 2 third order intermodulation output power (the b point among the figure) then will have very high dynamic range to spectrum analyzer so than much smaller times of single order intermodulation output power (a point among the figure).Secondly, can be known by Fig. 3 that the testing tool in the test block diagram is very complicated, various and cost an arm and a leg with equipment, whole test system is especially very high to wave filter, frequency spectrograph requirement, and these have increased the cost and the complicacy of test macro to a certain extent again.

Therefore, how to simplify test macro, reduce testing cost, improving testing efficiency is the major issue of being badly in need of solution at present.

Summary of the invention

The technical matters that (one) will solve

For addressing the above problem, significantly cut down testing cost, simplify test structure, the present invention utilizes the input-output curve of amplifier, especially N ₁DB compression point power input

With N ₂DB compression point power input

Difference DELTA, provide a kind of based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point.

(2) technical scheme

For achieving the above object, the invention provides a kind of based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point comprises: signal source, amplifier to be measured are connected with power meter successively; Signal source is to amplifier power input to be measured, and progressively strengthens power input, and power meter is measured the corresponding output power of each power input; According to power input and the output power measured, confirm N ₁DB compression point power input

And N ₂DB compression point power input

By N ₁DB compression point power input

And N ₂DB compression point power input

Calculate the difference DELTA of power input; This difference DELTA substitution third order intermodulation computing formula is calculated N ₁The power difference DELTA of dB compression point power input and third order intermodulation point power input _IIP3And to this power difference DELTA _IIP3Revise, obtain third order intermodulation point power input value.

(3) beneficial effect

Can find out that from technique scheme the present invention has following beneficial effect:

1, provided by the invention based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point; Only need to use a signal source and a power meter, thereby reduced the cost of test macro significantly, simplified test structure; After the process calculating of algorithm, thereby add that the corrected value correction can guarantee very high precision.

2, along with the development of microelectric technique, testing tool is more and more expensive, thereby causes the testing expense will be increasingly high.And it is provided by the invention based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point, very low to the requirement of testing expense, thus make the present invention will have bigger potentiality.

Description of drawings

Fig. 1 is the input and output spectrogram of double-tone test;

Fig. 2 is the definition figure of third order intermodulation;

Fig. 3 is the synoptic diagram of third order intermodulation test in the prior art;

Fig. 4 be by the amplifier input-output curve is confirmed

and difference DELTA synoptic diagram;

Fig. 5 be by amplifier input, gain trace is confirmed

and difference DELTA synoptic diagram;

Fig. 6 is based on N according to the embodiment of the invention ₁DB compression point and N ₂The synoptic diagram of the third order intermodulation test of dB compression point.

Embodiment

For making the object of the invention, technical scheme and advantage clearer, below in conjunction with specific embodiment, and with reference to accompanying drawing, to further explain of the present invention.

At first, to provided by the invention based on N ₁DB compression point and N ₂The related term of third order intermodulation method of testing of dB compression point is set forth.For amplifier; Output power and power input keep a stable gain value (Gain) when power input is in the linearity of amplifier district; And the yield value the when yield value of output power and power input will be less than linear zone when power input gets into the amplifier nonlinearity district; The yield value of this moment and the difference of linear zone yield value just equal NdB so, and this input and output power points is exactly the NdB compression point.Fig. 4 and Fig. 5 be from two different aspects, with different parametric representations this notion.

N ₁DB compression point power input

With N ₂DB compression point power input

Difference be Δ, can clearly find out and calculate and understand with gain diagram from Fig. 4 input and output power diagram and Fig. 5 input.Δ is brought into the third order intermodulation computing formula can calculates IIP3 and N ₁DB compression point power input Difference DELTA _IIP3, to this difference DELTA _IIP3Can obtain third order intermodulation point power input (IIP3) value after revising.

In calculation process; The amplifier inputoutput data is used for the wide variation data of complete record amplifier from the linear zone to the inelastic region; The input and output power of survey record amplifier in the scope of non-constant width; Begin to measure from miniwatt, measure the inelastic region, will surpass the 3dB compression point at least from linear zone.According to the inputoutput data of amplifier, confirm N ₁DB compression point and N ₂The dB compression point, the two power input difference and N according to it ₁DB compression point power input substitution third order intermodulation computing formula calculates third order intermodulation point power input (IIP3).

Set forth third order intermodulation calculating formula process below.For amplifier; Can be after its input signal process is amplified owing to the amplifier nonlinearity characteristic produces many higher order signals and derivative products thereof; Because mathematical analysis is too complicated, this formula is only considered (this has also considered the quadravalence signal that has the greatest impact in the higher order signal) till the five rank signals.The amplitude enlargement factor of supposing amplifier is a ₁, then desirable amplifier output signal: V _o=a ₁V _i

If input signal is: V _i=V _sCOS (ω t)

Then real output signal is: $V_o=a_1{V}_i+a_2{V}_i^2+a_3{V}_i^3+a_4{V}_i^4+a_5{V}_i^5---\left(1\right)$

When input signal is two-tone signal: V _i=V _s(cos ω ₁T+cos ω ₂T), launching in substitution (1) formula to calculate frequency is ω again ₁The single order signal be: $V_{o1}=(a_1{V}_s+\frac{9}{4}{a}_3{V}_s^3+\frac{25}{4}{a}_5{V}_s^5){\mathrm{Cos}\mathrm{\ω}}_{1}t$

Frequency is 2 ω ₁-ω ₂The third order intermodulation signal be: $V_{o3}=(\frac{3}{4}{a}_3{V}_s^3+\frac{25}{8}{a}_5{V}_s^5)\mathrm{Cos}({2\mathrm{\ω}}_1-{\mathrm{\ω}}_2)t$

In remaining derivation of equation process, do not consider the variation of signal phase, then will only calculate in afterwards the process, so be the simplification computing to amplitude owing to only consider the power of signal.

Frequency is ω ₁The single order signal be: $V_{o1}=a_1{V}_s+\frac{9}{4}{a}_3{V}_s^3+\frac{25}{4}{a}_5{V}_s^5---\left(2\right)$

Frequency is 2 ω ₁-ω ₂The third order intermodulation signal be: $V_{o3}=\frac{3}{4}{a}_3{V}_s^3+\frac{25}{8}{a}_5{V}_s^5---\left(3\right)$

For N ₁The dB compression point, establish:

The output power of this moment is:

For N ₂The dB compression point, establish:

The output power of this moment is:

And N ₁The output power at dB compression point place: $V_o^{N_1}=a_1{V}_1+\frac{9}{4}{a}_3{V}_1^3+\frac{25}{4}{a}_5{V}_1^5$

Simultaneous (4) Shi Kede: ${\mathrm{Aa}}_1=a_1+\frac{9}{4}{a}_3{V}_1^2+\frac{25}{4}{a}_5{V}_1^4---\left(6\right)$

And N ₁The output power at dB compression point place: $V_o^{N_2}=a_1{V}_2+\frac{9}{4}{a}_3{V}_2^3+\frac{25}{4}{a}_5{V}_2^5$

Simultaneous (5) Shi Kede: ${\mathrm{Ba}}_1=a_1+\frac{9}{4}{a}_3{V}_2^2+\frac{25}{4}{a}_5{V}_2^4---\left(7\right)$

For third order intermodulation point, the single order output power here: V _Oiip3-1=α ₁V ₃(8)

And the third order intermodulation output power here: $V_{\mathrm{Oiip}3-3}=\frac{3}{4}{a}_3{V}_3^3+\frac{25}{8}{a}_5{V}_3^5---\left(9\right)$

Can know V by the third order intermodulation definition _Oiip3-1With V _Oiip3-3Should equate, and a ₃, a ₅＜0, then in order to keep equating about equality:

V _oiip3-1＝-V _oiip3-3 (10)

Simultaneous (8) (9) (10) formula can be released; $a_1=-\frac{3}{4}{a}_3{V}_3^2-\frac{25}{8}{a}_5{V}_3^4---\left(11\right)$

(11) formula is separated quadratic equation with one unknown can solve: $V_3^2=\frac{-\frac{3}{4}{a}_3-\sqrt{\frac{9}{16}{a}_3^2-\frac{25}{2}{a}_5{a}_1}}{\frac{25}{4}{a}_5}---\left(12\right)$

Simultaneous (6), (7) formula can solve: $a_3=\frac{4(\frac{A-1}{V_1^4}-\frac{B-1}{V_2^4})}{9(\frac{1}{V_1^2}-\frac{1}{V_2^2})}{a}_1---\left(13\right)$

$a_5=\frac{{4a}_1}{25(V_2^2-V_1^2)}(\frac{B-1}{V_2^2}-\frac{A-1}{V_1^2})---\left(14\right)$

And for

Suppose: $V_2^2={10}^x*V_1^2---\left(15\right)$

With (13), (14), (15) substitution (12) Shi Kede:

$V_3^2=\frac{\frac{(1-A-\frac{1-B}{{10}^{2x}})}{3(1-\frac{1}{{10}^x})}-\sqrt{\frac{{(1-A-\frac{1-B}{{10}^{2x}})}^2}{9{(1-\frac{1}{{10}^x})}^2}-\frac{2}{{10}^x-1}(1-A-\frac{1-B}{{10}^x})}}{\frac{1}{{10}^x-1}(1-A-\frac{1-B}{{10}^x})}{V}_1^2---\left(16\right)$

Set N at present ₁DB and N ₂Power input difference between the dB compression point is Δ dB, then for (16) formula: $x=\frac{\mathrm{\Δ}}{10}---\left(17\right)$

With

with; (17) formula substitution; (16) Shi Kede:

$V_3^2\text{=}\frac{\frac{(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{-N_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{5}}})}{3(1-\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}})}-\sqrt{\frac{{(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{5}}})}^2}{9{(1-\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}})}^2}-\frac{2}{{10}^{\frac{\mathrm{\Δ}}{10}}-1}(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{10}}})}}{\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}-1}(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{-N_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{10}}})}{V}_1^2$

Suppose:

${\mathrm{\Δ}}_{\mathrm{IIP}3}=10\lg \left(\frac{\frac{(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{5}}})}{3(1-\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}})}-\sqrt{\frac{{(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{5}}})}^2}{9{(1-\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}})}^2}-\frac{2}{{10}^{\frac{\mathrm{\Δ}}{10}}-1}(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{10}}})}}{\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}-1}(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{10}}})}\right)$

Then transformed into logarithmic power:

which can be:

And in the actual measurement process because this formula has been ignored more than five rank more high-order harmonic wave to the influence of signal power, so need add a modified value Δ _Revise, this modified value changes according to different test environments to some extent, needs when first test, to proofread and correct.To sum up can get: $\mathrm{IIP}3=P_{N_1\mathrm{DB}}+{\mathrm{\Δ}}_{\mathrm{IIP}3}+{\mathrm{\Δ}}_{\mathrm{Revise}}.$

Provided by the invention based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point mainly comprises amplifier inputoutput data (curve), N ₁DB and N ₂The dB compression point is chosen, N ₁-N ₂Input work rate variance and third order intermodulation calculate.Wherein, amplifier inputoutput data (curve) is used for the wide variation data of complete record amplifier from the linear zone to the inelastic region; N ₁DB and N ₂It is on the amplifier input-output curve, to determine linear zone and inelastic region that the dB compression point is chosen, and in the inelastic region, chooses two compression point-N ₁DB compression point and N ₂The dB compression point; N ₁-N ₂Input work rate variance: calculate the N that chooses ₁DB compression point and N ₂The difference of dB compression point power input; Third order intermodulation calculates: according to N ₁-N ₂Input work rate variance and N ₁-N ₂The third order intermodulation point of output work rate variance computing amplifier.

The present invention need be in the scope of non-constant width the input and output power of survey record amplifier, begin to measure from miniwatt, measure the inelastic region from linear zone, to surpass the 3dB compression point at least.Reach the amplifier power input upper limit if power input is too early, then measurement range is exceeded with the amplifier power input upper limit.Determine linear zone and inelastic region according to the inputoutput data of amplifier, in the inelastic region, confirm N ₁DB compression point and N ₂The dB compression point.According to the N that chooses ₁DB compression point and N ₂The difference of dB compression point power input is calculated its two power input difference N ₁-N ₂The input work rate variance.Then according to the N that calculates ₁-N ₂Input work rate variance and N ₁, N ₂Calculate the third order intermodulation point.

Be example with a radio frequency amplifier below, utilize provided by the invention based on N ₁DB compression point and N ₂The dB compression point is carried out the third order intermodulation method of testing, tests the third order intermodulation point power input IIP3 of amplifier to be measured.

Fig. 6 shows according to the embodiment of the invention based on N ₁DB compression point and N ₂The synoptic diagram of the third order intermodulation test of dB compression point may further comprise the steps:

Step 1: signal source, amplifier to be measured are connected with power meter successively, as shown in Figure 6;

Step 2: signal source begins to amplifier power input to be measured from the miniwatt of-30dBm, and is progressively to strengthen power input at interval with 0.1dBm, and power meter is measured the corresponding output power of each power input;

Step 3: according to power input and the output power measured, confirm Amplifier Gain, linear zone and inelastic region, in the inelastic region, select N ₁DB compression point and N ₂DB compression point, and then definite N ₁DB compression point power input

And N ₂DB compression point power input

Step 4: by N ₁DB compression point power input

And N ₂DB compression point power input Calculate the difference DELTA of power input:

Step 5: this difference DELTA substitution third order intermodulation computing formula is calculated N ₁The power difference DELTA of dB compression point power input and third order intermodulation point power input (IIP3) _IIP3:

${\mathrm{\Δ}}_{\mathrm{IIP}3}=10\lg \left(\frac{\frac{(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{5}}})}{3(1-\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}})}-\sqrt{\frac{{(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{5}}})}^2}{9{(1-\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}})}^2}-\frac{2}{{10}^{\frac{\mathrm{\Δ}}{10}}-1}(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{10}}})}}{\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}-1}(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{10}}})}\right)$

Wherein,

is the power input of power gain during less than amplifier gain N1dB of this moment,

be the power input of power gain at this moment during less than amplifier gain N2dB.

Step 6: to this power difference DELTA _IIP3Revise, promptly add modified value again and can further calculate more accurate third order intermodulation point power input (IIP3):

Δ wherein _ReviseBe modified value.

Provided by the invention based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point only needs to use a signal source and a power meter, thereby reduces the cost of test macro significantly, and simple in structure.After the process calculating of algorithm, thereby add that the corrected value correction can guarantee very high precision.Along with the development of microelectric technique, testing tool is more and more expensive, thereby causes the testing expense will be increasingly high.And it is provided by the invention based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point, very low to the requirement of testing expense, thus make the present invention will have bigger potentiality.

Above-described specific embodiment; The object of the invention, technical scheme and beneficial effect have been carried out further explain, and institute it should be understood that the above is merely specific embodiment of the present invention; Be not limited to the present invention; All within spirit of the present invention and principle, any modification of being made, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (6)

1. one kind based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point is characterized in that, comprising:

Signal source, amplifier to be measured are connected with power meter successively;

Signal source is to amplifier power input to be measured, and progressively strengthens power input, and power meter is measured the corresponding output power of each power input;

According to power input and the output power measured, confirm N ₁DB compression point power input And N ₂DB compression point power input

By N ₁DB compression point power input

And N ₂DB compression point power input

Calculate the difference DELTA of power input;

This difference DELTA substitution third order intermodulation computing formula is calculated N ₁The power difference DELTA of dB compression point power input and third order intermodulation point power input _IIP3And

To this power difference DELTA _IIP3Revise, obtain third order intermodulation point power input value.

2. according to claim 1 based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point; It is characterized in that said signal source is to amplifier power input to be measured, and progressively strengthen in the step of power input; Signal source is to begin to amplifier power input to be measured from-30dBm, and is progressively to strengthen power input at interval with 0.1dBm.

3. according to claim 1 based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point is characterized in that, and is said according to power input and the output power measured, confirms N ₁DB compression point power input and N ₂The step of dB compression point power input comprises:

According to power input and the output power measured, confirm Amplifier Gain, linear zone and inelastic region, in the inelastic region, select N ₁DB compression point and N ₂DB compression point, and then definite N ₁DB compression point power input and N ₂DB compression point power input.

4. according to claim 1 based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point is characterized in that, and is said by N ₁DB compression point power input And N ₂DB compression point power input

In the step of the difference DELTA of calculating power input, the difference of power input $\mathrm{\Δ}={\mathrm{Pi}}_{N_2\mathrm{DB}}-{\mathrm{Pi}}_{N_1\mathrm{DB}}.$

5. according to claim 1 based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point is characterized in that, said this difference DELTA substitution third order intermodulation computing formula is calculated N ₁The power difference DELTA of dB compression point power input and third order intermodulation point power input _IIP3Step in, said third order intermodulation computing formula is:

${\mathrm{\Δ}}_{\mathrm{IIP}3}=10\lg \left(\frac{\frac{(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{5}}})}{3(1-\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}})}-\sqrt{\frac{{(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{5}}})}^2}{9{(1-\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}})}^2}-\frac{2}{{10}^{\frac{\mathrm{\Δ}}{10}}-1}(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{10}}})}}{\frac{1}{{10}^{\frac{\mathrm{\Δ}}{10}}-1}(1-{10}^{\frac{{-N}_1}{20}}-\frac{1-{10}^{\frac{{-N}_2}{20}}}{{10}^{\frac{\mathrm{\Δ}}{10}}})}\right)$

Wherein,

is the power input of power gain during less than amplifier gain N1dB of this moment,

be the power input of power gain at this moment during less than amplifier gain N2dB.

6. according to claim 1 based on N ₁DB compression point and N ₂The third order intermodulation method of testing of dB compression point is characterized in that, and is said to this power difference DELTA _IIP3Revise, obtain in the step of third order intermodulation point power input value, to this power difference DELTA _IIP3Revise is to adopt formula

In this power difference DELTA _IIP3On add the modified value Δ again _Revise, obtain third order intermodulation point power input value, wherein Δ _ReviseBe modified value.

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