CN106301231A - A kind of local oscillator noise counteracting method and circuit - Google Patents

Abstract

The invention provides a kind of local oscillator noise counteracting method and circuit, this circuit includes two frequency mixers, wherein the rf inputs of the first frequency mixer connects radio-frequency input signals, second frequency mixer rf inputs connects a load, local oscillation signal source is connected with the local oscillation signal input of the first frequency mixer and the second frequency mixer respectively, the medium frequency output end of the first frequency mixer and the second frequency mixer is respectively connected to subtraction device, is offset the local oscillator noise comprised in the intermediate-freuqncy signal of the first frequency mixer output by subtraction device.The present invention can improve the quality of the first mixer output signal, promotes the linearity and the sensitivity of mixer output signal when small-signal inputs.

Description

A kind of local oscillator noise counteracting method and circuit

Technical field

The present invention relates to technical field of radio, particularly relate to a kind of local oscillator noise counteracting method and electricity Road.

Background technology

In technical field of radio, the frequency changer circuit being made up of local oscillator and frequency mixer is widely used in bag Include in the middle of the radio systems such as mobile communication, satellite navigation, radar, remote sensing, signal measurement and metering.

When in the ideal case, local oscillator is single-frequency spectral line or frequency mixer is preferable double balanced mixer Time, in the case of radio frequency input does not input, frequency mixer does not has intermediate frequency component to export.But due to Being limited by technique, frequency mixer cannot accomplish that preferable double flat weighs, and local oscillation signal frequency spectrum also cannot be accomplished single Spectral line, therefore in the case of rf inputs does not input, the medium frequency output end of frequency mixer has local oscillator Phase noise signal exports.This phenomenon is particularly evident at millimeter wave frequency band, because at millimeter wave frequency band signal Commonly used frequency multiplication source, source, after frequency multiplication, signal spectrum purity is deteriorated, and has bigger at nearby carriers Phase noise and other clutters.Therefore, even if the input of frequency mixer rf inputs is zero, as There is the problem that local oscillation signal oneself is multiplied, cause the medium frequency output end of frequency mixer to produce intermediate-freuqncy signal, should Phenomenon is referred to as frequency mixer self-mixing.The intermediate-freuqncy signal of self-mixing can form interference to tested intermediate-freuqncy signal, Introduce measurement error, reduce the sensitivity of receiver.

Summary of the invention

In view of this, the invention provides a kind of local oscillator noise counteracting method and circuit.

Based on the embodiment of the present invention, the present invention provides a kind of local oscillator noise counteracting method, the method bag Include:

The local oscillation signal of local oscillation signal source output is divided into two-way and is respectively connected to the first frequency mixer and the second frequency mixer；

First frequency mixer is received radio-frequency input signals as primary work frequency mixer, its rf inputs；

The auxiliary frequency mixer offset as local oscillator noise by second frequency mixer, its rf inputs connects One load；

Two output end signals of the first frequency mixer and the second frequency mixer do local oscillator noise through subtraction device and offset After, the output signal of subtraction device is exported as IF output signal.

Further, the local oscillator noise signal amplitude by adjusting the second mixer output output is offset The local oscillator noise signal of the first mixer output output.

Further, between the first frequency mixer and local oscillation signal source, add the first isolator, in the second mixing The second isolator is added, to reduce radiofrequency signal crosstalk between device and local oscillation signal source.

Further, by power splitter, the local oscillation signal that local oscillation signal source exports is divided into two-way and is respectively connected to The input of the local oscillation signal of one frequency mixer and the second frequency mixer.

Further, by directional coupler, the local oscillation signal that local oscillation signal source exports is divided into two-way, orientation The principal arm of bonder is input to the first frequency mixer, the output signal amplified device input of the other arm of directional coupler To the second frequency mixer.

Based on the embodiment of the present invention, the present invention provides the bucking circuit of a kind of local oscillator noise, this circuit Including: the first frequency mixer, the second frequency mixer, local oscillation signal source, subtraction device；

The local oscillation signal of local oscillation signal source output is separately input to the local oscillator letter of the first frequency mixer and the second frequency mixer Number input；

The rf inputs of the first frequency mixer receives radio-frequency input signals；

The rf inputs of the second frequency mixer connects a load；

First frequency mixer and the second frequency mixer outfan output signal access subtraction device, the first frequency mixer and Two output end signals of the second frequency mixer do after local oscillator noise offsets through subtraction device, defeated by subtraction device Go out signal to export as intermediate-freuqncy signal.

Further, being provided with amplitude adjusting circuit in described subtraction device, described amplitude adjusting circuit is used for adjusting The local oscillator noise signal amplitude of whole second frequency mixer output so that the basis of the second mixer output output Phase noise signal amplitude of shaking is equal with the amplitude of the local oscillator noise signal that the first mixer output exports, Thus offset the local oscillator noise of the first mixer output output.

Further, described circuit also includes: the first isolator, and one end receives local oscillation signal, the other end Access the local oscillation signal input of the first frequency mixer；With

Second isolator, one end receives local oscillation signal, and the local oscillation signal that the other end accesses the second frequency mixer is defeated Enter end.

Further, described circuit also includes: power splitter, for the local oscillation signal exported in local oscillation signal source It is divided into two-way, is respectively connected to the input of the local oscillation signal of the first frequency mixer and the second frequency mixer.

Further, described circuit also includes: directional coupler, for the local oscillator exported in local oscillation signal source Signal is divided into two-way, and the output signal of the principal arm of directional coupler accesses the local oscillation signal input of the first frequency mixer End, the output signal of other arm accesses amplifier in；With

Amplifier, the output signal for arm other to directional coupler is amplified, its outfan and second The local oscillation signal input of frequency mixer connects.

The bucking circuit of the local oscillator noise that the present invention provides includes two frequency mixers, wherein first mixes Frequently device connects radio-frequency input signals as primary work frequency mixer (main frequency mixer), its rf inputs, Second frequency mixer rf inputs connects a load, and local oscillation signal source is mixed with the first frequency mixer and second respectively The local oscillation signal input of device connects, and the medium frequency output end of the first frequency mixer and the second frequency mixer is respectively connected to Subtraction device, offsets the local oscillator noise comprised in the first mixer output signal by subtraction device.This The bright quality that can improve the first mixer output signal, mixer output signal when promoting small-signal input The linearity and sensitivity.

Accompanying drawing explanation

Figure 1A is the circuit theory diagrams of double balanced mixer；

Figure 1B is the circuit theory diagrams that double balanced mixer is operated in the positive half cycle of local oscillation signal；

Fig. 1 C is the circuit theory diagrams that double balanced mixer is operated in local oscillation signal negative half period；

The local oscillation signal bucking circuit theory structure schematic diagram that Fig. 2 provides for the embodiment of the present invention；

Subtraction circuit theory structure in the local oscillation signal bucking circuit that Fig. 3 provides for one embodiment of the invention Schematic diagram；

Circuit in the local oscillation signal bucking circuit of the band isolator that Fig. 4 provides for one embodiment of the invention is former Reason structural representation；

Circuit in the local oscillation signal bucking circuit of the band power splitter that Fig. 5 provides for one embodiment of the invention is former Reason structural representation；

In the local oscillation signal bucking circuit of the employing directional coupler that Fig. 6 provides for one embodiment of the invention Circuit principle structure schematic diagram.

Detailed description of the invention

For making the purpose of the application, technical scheme and advantage clearer, referring to the drawings to this Apply for that described scheme is described in further detail.When explained below relates to accompanying drawing, unless otherwise indicated, Same numbers in different accompanying drawings represents same or analogous key element.Described in following exemplary embodiment Embodiment do not represent all embodiments consistent with the application.On the contrary, they be only with such as The example of the apparatus and method that some aspects that described in detail in appended claims, the application are consistent.

It is only merely for describing the purpose of specific embodiment at term used in this application, and is not intended to be limiting The application." a kind of " of singulative used in the application and appended claims, " institute State " and " being somebody's turn to do " be also intended to include most form, unless context clearly shows that other implications.Also should Work as understanding, term "and/or" used herein refer to and comprise one or more be associated list item Any or all possible combination of purpose.

Although should be appreciated that may use term first, second, third, etc. various to describe in the application Information, but these information should not necessarily be limited by these terms.These terms only be used for by same type of information that This distinguishes.Such as, in the case of without departing from the application scope, the first information can also be referred to as Two information, similarly, the second information can also be referred to as the first information.Depend on linguistic context, as in this institute Use word " if " can be construed to " and ... time " or " when ... time " or " response In determining ".

Double balanced mixer ultimate principle refer to shown in Fig. 1, and wherein Figure 1A is the circuit of frequency mixer, Figure 1B It is operated in circuit when the positive half cycle of local oscillation signal and negative half period with Fig. 1 C respectively frequency mixer.

The electric current of diode and voltage I-V characteristic can use formula (1) to represent

I=a₀+a₁u+a₂u² (1)

Formula have ignored higher order term, because the higher order term signal produced after Hun Pin, permissible after low-pass filtered device Filter.Half cycle positive for local oscillator, the voltage signal on two diode D1 and D3 is

u₁=u₀+u_s

(2)

u₃=u₀-u_s

In formula, u₀、u_sIt is respectively local oscillation signal and radiofrequency signal.Diode D1 and D3 current signal are

i₁=a_d1-0+a_d1-1(u₀+u_s)+a_d1-2(u₀+u_s)²

(3)

i₃=a_d3-0+a_d3-1(u₀-u_s)+a_d3-2(u₀-u_s)²

Mixer intermediate-frequency end output signal is

$\begin{array}{c}{u}_i=(i_1-i_3)R_L\\ =R_L[(a_{d1-0}-a_{d3-0})+a_{d1-1}(u_0+u_s)-a_{d3-1}(u_0-u_s)+a_{d1-2}{(u_0+u_s)}^2-a_{d3-2}{(u_0-u_s)}^2]\\ =R_L[(a_{d1-0}-a_{d3-0})+(a_{d1-1}-a_{d3-1})u_0+(a_{d1-1}+a_{d3-1})u_s\\ +(a_{d1-2}-a_{d3-2})(u_0^2+u_s^2)+2(a_{d1-2}+a_{d3-2})u_0{u}_s]\\ \≈R_L[\mathrm{\Δ}{a}_0+\mathrm{\Δ}{a}_1{u}_0+2a_1{u}_s+\mathrm{\Δ}{a}_2(u_0^2+u_s^2)+4a_2{u}_0{u}_s]\end{array}---\left(4\right)$

In formula, (a_d1-1+a_d3-1)≈2a₁；(a_d1-2+a_d3-2)≈2a₂.For ideal situation, diode D1 Being identical with the I-V characteristic of D2, D1 and D2 passage path is isometric；The centre cap of coil in , at this moment there is Δ a heart positions etc.₀=0, Δ a₁=0, Δ a₂=0, the output of double balanced mixer intermediate frequency is except radiofrequency signal Outward, difference frequency (ω is only comprised₀-ω_s) and and frequency (ω₀+ω_s) item, i.e.

$\begin{array}{c}{u}_i=2R_L{a}_1{u}_s-4R_L{a}_2{u}_0{u}_s\\ =2R_L{a}_1{u}_s-2R_L{a}_2{U}_0{U}_s\mathrm{Re}(e^{j({\mathrm{\ω}}_0-{\mathrm{\ω}}_s)t}+e^{j({\mathrm{\ω}}_0+{\mathrm{\ω}}_s)t})\end{array}---\left(5\right)$

Actual frequency mixer not ideal component, Δ a₀, Δ a₁, Δ a₂All it is not zero, causes in frequency mixer Frequency output has local oscillator noise signal.Commercial frequency mixer all provides local oscillator and intermediate frequency and local oscillator and radio frequency Isolation, generally 20dB to 30dB, if using Δ a₁Represent all undesirable components, it is assumed that Δ a₁For -25dB；2a₂It is conversion loss, generally about 6dB.

When local oscillator has interference signal e at nearby carriers₀Time, the intermediate frequency of frequency mixer is output as

$\begin{array}{c}{u}_i=(i_1-i_3)R_L\\ =R_L[(a_{d1-0}-a_{d3-0})+a_{d1-1}(u_0+u_s+e_0)-a_{d3-1}(u_0-u_s+e_0)+a_{d1-2}{(u_0+u_s+e_0)}^2-a_{d3-2}{(u_0-u_s+e_0)}^2]\\ \≈R_L[\mathrm{\Δ}{a}_0+\mathrm{\Δ}{a}_1(u_0+e_s)+2a_1{u}_s+\mathrm{\Δ}{a}_2(u_0^2+u_s^2+e_s^2+2u_0{e}_s)+4a_2(u_0{u}_s+u_s{e}_s)]\end{array}---\left(6\right)$

From formula (6), the intermediate frequency end output of frequency mixer comprise intermediate frequency, local oscillator, radio frequency and radio frequency and Local frequency and item, after low pass filter, only remain by 4R_La₂u₀u_sAnd 2R_LΔa₂u₀e₀Produce intermediate frequency ?WithAssume conversion loss 2a₂For-6dB Left and right；Δa₂≈Δa₁, i.e. Δ a₂Also it is-25dB, then Δ a₂Compare 2a₂Low 19dB, works as e₀Equal to frequency mixer During rf inputs signal, e₀The maximum error introducing measurement intermediate-freuqncy signal is 11%, and so-called maximum error refers to Work as e₀With radiofrequency signal homophase or anti-phase time, introduce maximum error, when other phase place, this error diminishes. Crosstalk signal e₀Impact on measuring can use formula (7) to represent

$\mathrm{\Δ}{A}_m=\±8.69\sqrt{\frac{p_n}{p_s}}\mathrm{dB}---\left(7\right)$

In formula, P_n、P_sIt is respectively defined in the clutter signal levels of mixer intermediate-frequency output and tested intermediate-freuqncy signal. From formula (7) it can be seen that when the amplitude of radiofrequency signal diminishes, disturb the intermediate frequency that frequency mixer is exported by signal The impact of signal can become big.

Understand based on above-mentioned analysis, owing to frequency mixer cannot accomplish that preferable double flat weighs, and local oscillation signal frequency The non-singlet line of spectrum, causes the self-mixing of frequency mixer, therefore in the case of rf inputs does not input, The medium frequency output end of frequency mixer has the output of local oscillator noise signal.In order to suppress local oscillator noise to mixed The impact of the intermediate-freuqncy signal of device output frequently, improves the linearity when frequency mixer receives or measure small-signal and spirit Sensitivity, the invention provides a kind of local oscillator noise counteracting method and circuit, with reference to the circuit knot of Fig. 2 Composition, this circuit includes local oscillation signal source LO, the first frequency mixer M1, the second frequency mixer M2, subtraction device S, The method comprises the steps:

The local oscillation signal of step 100, local oscillation signal source LO output is divided into two-way and is respectively connected to the first frequency mixer M1 With the second frequency mixer M2；

Step 102, using the first frequency mixer M1 as primary work frequency mixer, its rf inputs receives radio frequency Input signal RF；

Step 104, the auxiliary frequency mixer offset as local oscillator noise by the second frequency mixer M2, it is penetrated Frequency input terminal connects a load LOAD；

Two frequency mixer output intermediate-freuqncy signals of step 106, the first frequency mixer M1 and the second frequency mixer M2 are through phase Subtract device S do local oscillator noise offset after, using the output signal of subtraction device as IF output signal.

Refer to Fig. 2 example, the bucking circuit of the local oscillator noise that the present invention provides includes two frequency mixers, Wherein the first frequency mixer is as the primary work frequency mixer of real work, and its rf inputs is used for receiving reality External radio frequency input signal to be processed, and the second frequency mixer wraps for offsetting in the first mixer output signal The local oscillator noise contained, the second frequency mixer rf inputs connects a load.Based on frequency mixer above certainly Mixing principle analysis, two frequency mixers all contain the local oscillator noise that self-mixing produces Local oscillator noise in the output signal of two frequency mixers is relevant, the invention The relevant local oscillator phase place included in output offset first mixer output signal of the second frequency mixer is used to make an uproar Sound, thus improve the quality of the first mixer intermediate-frequency output signal, frequency mixer output when promoting small-signal input The linearity of signal and sensitivity.

In one embodiment of this invention, subtraction device realizes using circuit structure as shown in Figure 3, real at this Execute the local oscillator using the operational amplifier of high precision to realize in the two paths of signals of two frequency mixer outputs in example The counteracting of phase noise processes, and the output signal of two frequency mixers can be respectively connected to computing according to application scenarios and put The homophase of big device and inverting input, or anti-phase and in-phase input end, the output of operational amplifier is as subtracting each other The output signal output of device.

Further, owing to two frequency mixer balance qualities exist difference, the therefore output letter of two frequency mixers Also amplitude difference can be there is, in order to reduce local oscillator noise further in number local oscillator noise comprised Impact, adds amplitude adjusting circuit in subtraction device in present example, in this circuit, the first frequency mixer is i.e. The outfan of primary work frequency mixer accesses the inverting input of operational amplifier, and use i.e. offset by the second frequency mixer Auxiliary frequency mixer outfan by one adjustable potentiometer access operational amplifier in-phase input end.This is real The effect of adjustable potentiometer in example of executing is to adjust signal amplitude, makes the local oscillator that two-way is input in operational amplifier Phase noise signal amplitude is equal, to reach to offset the local oscillator comprised in the first mixer output signal accurately The purpose of phase noise.

In order to prevent radiofrequency signal from forming crosstalk after passing through frequency mixer, in embodiments of the present invention, refer to Fig. 4 Example, adds the first isolator ISO1 between the first frequency mixer M1 and local oscillation signal source LO, mixes second Frequently the second isolator ISO2 is added between device M2 and local oscillation signal source LO.

In the embodiment of the present invention, refer to Fig. 5 example, by power splitter DIV by local oscillation signal portion be The two-way output signal of two, power splitter DIV is separately input to the first frequency mixer M1 and the second frequency mixer M2 Input, wherein, add power splitter effect be that local oscillation signal is divided into two paths of signals, local oscillator believe In the case of number source level magnitudes is limited, owing to being not enough to drive frequency mixer after power splitter is decayed, then may be used Directional coupler is selected to be used as power splitter.

In an embodiment of the present invention, the signal inputting the first frequency mixer is the millimeter wave frequency more than 50GHz Section, local oscillation signal level magnitudes is limited, is not enough to drive frequency mixer, therefore uses after using power splitter decay 10dB directional coupler, such as Fig. 6 example, the principal arm of directional coupler CUP is input to the first frequency mixer M1, The other arm output of 10dB directional coupler CUP is input to the second frequency mixer M2 through millimeter wave amplifier AMP, The rf inputs of the second frequency mixer M2 meets a waveguide load LOAD, and the principle of cancellation of local oscillator noise sees Above-mentioned analysis process, here is omitted.Owing to the phase noise of frequency mixer output is local oscillator carrier wave and phase The function of position noise mutual relation, although the road that local oscillator is walked is through difference, electrical length is different, but does not affect two The dependency of individual mixer intermediate-frequency output.

Local oscillator noise (i.e. output signal after self-mixing Signal averaging noise) due to frequency mixer output Amplitude is little, it has not been convenient to see whether to be completely counterbalanced by, in conjunction with the example of earlier figures 3, in order to adjust subtraction device electricity The amplitude that road makes two-way export is equal, reaches the purpose of the local oscillator noise of offset measurement frequency mixer output, Therefore following means can be used to the amplitude adjusting circuit adjusting in subtraction device: turning off penetrating of the first frequency mixer Under the state of frequency input, arranging local oscillation signal source is amplitude modulation output, during frequency modulating signal is set to need Again and again rate, modulation depth is 0.5%, and at this moment mixer output signal is relatively big, adjusts phase under large-scale condition Subtracting device circuit, the output making subtraction device circuit is minimum.After adjusting, local oscillator closes modulation, recovers continuous wave Output.

Through actual circuit test, the local oscillator noise counteracting method of present invention offer and circuit, it is possible to Improve mixer intermediate-frequency output more than phase noise 20dB, improve the linearity and the sensitivity of weak-signal measurement. The local oscillator noise counteracting method that the present invention provides can be used for receiver, Radar Design, improves and measures little letter Number linear and sensitivity；Can also be used for signal analysis measurement apparatus, reduce the shadow that local oscillator noise introduces Ring；Can also be used for phase noise measurement device, reduce the impact that local oscillator noise introduces.

The foregoing is only presently preferred embodiments of the present invention, not in order to limit the present invention, all at this Within the spirit of invention and principle, any modification, equivalent substitution and improvement etc. done, should be included in Within the scope of protection of the invention.

Claims (10)

1. a local oscillator noise counteracting method, it is characterised in that described method includes:

The local oscillation signal of local oscillation signal source output is divided into two-way and is respectively connected to the first frequency mixer and the second frequency mixer；

First frequency mixer is received radio-frequency input signals as primary work frequency mixer, its rf inputs；

The auxiliary frequency mixer offset as local oscillator noise by second frequency mixer, its rf inputs connects One load；

Two output end signals of the first frequency mixer and the second frequency mixer do local oscillator noise through subtraction device and offset After, the output signal of subtraction device is exported as IF output signal.

2. the method for claim 1, it is characterised in that defeated by adjusting the second mixer output The local oscillator noise signal amplitude gone out offsets the local oscillator noise signal of the first mixer output output.

3. the method for claim 1, it is characterised in that in the first frequency mixer and local oscillation signal source it Between add the first isolator, between the second frequency mixer and local oscillation signal source, add the second isolator, with reduce Radiofrequency signal crosstalk.

4. the method as described in claim 1,2 or 3, it is characterised in that local oscillator is believed by power splitter The local oscillation signal of number source output is divided into two-way and is respectively connected to the local oscillation signal of the first frequency mixer and the second frequency mixer Input.

5. the method as described in claim 1,2 or 3, it is characterised in that incite somebody to action this by directional coupler The local oscillation signal of signal source of shaking output is divided into two-way, and the principal arm of directional coupler is input to the first frequency mixer, fixed It is input to the second frequency mixer to the amplified device of output signal of the other arm of bonder.

6. the bucking circuit of a local oscillator noise, it is characterised in that this circuit includes: the first frequency mixer, Second frequency mixer, local oscillation signal source, subtraction device；

The local oscillation signal of local oscillation signal source output is separately input to the local oscillator letter of the first frequency mixer and the second frequency mixer Number input；

The rf inputs of the first frequency mixer receives radio-frequency input signals；

The rf inputs of the second frequency mixer connects a load；

First frequency mixer and the second frequency mixer outfan output signal access subtraction device, the first frequency mixer and Two output end signals of the second frequency mixer do after local oscillator noise offsets through subtraction device, defeated by subtraction device Go out signal to export as intermediate-freuqncy signal.

7. circuit as claimed in claim 6, it is characterised in that the amplitude that is provided with in described subtraction device adjusts Circuit, the local oscillator noise signal amplitude that described amplitude adjusting circuit exports for adjustment the second frequency mixer, Make local oscillator noise signal amplitude and the first mixer output output of the second mixer output output The amplitude of local oscillator noise signal equal, thus offset the local oscillator phase place of the first mixer output output Noise.

8. circuit as claimed in claim 6, it is characterised in that described circuit also includes:

First isolator, one end receives local oscillation signal, and the local oscillation signal that the other end accesses the first frequency mixer is defeated Enter end；

Second isolator, one end receives local oscillation signal, and the local oscillation signal that the other end accesses the second frequency mixer is defeated Enter end.

9. the circuit as described in claim 6,7 or 8, it is characterised in that described circuit also includes:

Power splitter, for the local oscillation signal that local oscillation signal source exports is divided into two-way, is respectively connected to the first mixing The input of the local oscillation signal of device and the second frequency mixer.

10. the circuit as described in claim 6,7 or 8, it is characterised in that described circuit also includes:

Directional coupler, for the local oscillation signal that local oscillation signal source exports is divided into two-way, directional coupler The output signal of principal arm accesses the local oscillation signal input of the first frequency mixer, and the output signal of other arm accesses amplifies Device input；

Amplifier, the output signal for arm other to directional coupler is amplified, its outfan and second The local oscillation signal input of frequency mixer connects.