CN106301231B - Local oscillator phase noise cancellation method and circuit - Google Patents
Local oscillator phase noise cancellation method and circuit Download PDFInfo
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- CN106301231B CN106301231B CN201510239258.1A CN201510239258A CN106301231B CN 106301231 B CN106301231 B CN 106301231B CN 201510239258 A CN201510239258 A CN 201510239258A CN 106301231 B CN106301231 B CN 106301231B
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Abstract
The invention provides a local oscillator phase noise cancellation method and a local oscillator phase noise cancellation circuit, wherein the circuit comprises two mixers, wherein a radio frequency input end of a first mixer is connected with a radio frequency input signal, a radio frequency input end of a second mixer is connected with a load, local oscillator signal sources are respectively connected with local oscillator signal input ends of the first mixer and the second mixer, intermediate frequency output ends of the first mixer and the second mixer are respectively connected with a phase reducer, and local oscillator phase noise contained in an intermediate frequency signal output by the first mixer is cancelled through the phase reducer. The invention can improve the quality of the output signal of the first mixer and improve the linearity and the sensitivity of the output signal of the mixer when small signals are input.
Description
Technical Field
The present invention relates to the field of radio technologies, and in particular, to a local oscillator phase noise cancellation method and circuit.
Background
In the field of radio technology, frequency conversion circuits composed of local oscillators and mixers are widely used in radio systems including mobile communication, satellite navigation, radar, remote sensing, signal measurement and metering, etc.
When ideally the local oscillator is a single frequency spectral line or the mixer is an ideal double balanced mixer, the mixer has no intermediate frequency component output in the absence of an input at the RF input. However, due to the process limitation, the frequency mixer cannot achieve ideal double balance, and the local oscillator signal spectrum cannot achieve a single spectral line, so that the local oscillator phase noise signal is output at the intermediate frequency output end of the frequency mixer under the condition that no input is provided at the radio frequency input end. The phenomenon is particularly obvious in a millimeter wave frequency band, because a frequency doubling source is generally adopted in a millimeter wave frequency band signal source, the signal spectrum purity is poor after frequency doubling, and large phase noise and other clutters exist near a carrier wave. Therefore, even if the input at the rf input of the mixer is zero, the local oscillator signal is multiplied by itself, which causes the if output of the mixer to generate an if signal, and this phenomenon is called self-mixing of the mixer. The self-mixing intermediate frequency signal can interfere with the measured intermediate frequency signal, measurement errors are introduced, and the sensitivity of the receiver is reduced.
Disclosure of Invention
In view of the above, the present invention provides a local oscillation phase noise cancellation method and circuit.
Based on the embodiment of the invention, the invention provides a local oscillator phase noise cancellation method, which comprises the following steps:
the local oscillator signal output by the local oscillator signal source is divided into two paths and respectively accessed to the first frequency mixer and the second frequency mixer;
the first frequency mixer is used as a main working frequency mixer, and a radio frequency input end of the first frequency mixer receives a radio frequency input signal;
the second mixer is used as an auxiliary mixer for offsetting local oscillation phase noise, and the radio frequency input end of the second mixer is connected with a load;
after signals at two output ends of the first frequency mixer and the second frequency mixer are subjected to local oscillation phase noise cancellation through the phase subtracter, the output signals of the phase subtracter are output as intermediate frequency output signals.
Further, the local oscillator phase noise signal output by the output end of the first frequency mixer is offset by adjusting the amplitude of the local oscillator phase noise signal output by the output end of the second frequency mixer.
Further, a first isolator is added between the first mixer and the local oscillator signal source, and a second isolator is added between the second mixer and the local oscillator signal source, so that radio frequency signal crosstalk is reduced.
Furthermore, the local oscillator signal output by the local oscillator signal source is divided into two paths by the power divider and is respectively connected to the input ends of the local oscillator signals of the first frequency mixer and the second frequency mixer.
Furthermore, the local oscillator signal output by the local oscillator signal source is divided into two paths by the directional coupler, a main arm of the directional coupler is input into the first mixer, and an output signal of a side arm of the directional coupler is input into the second mixer through the amplifier.
Based on the embodiment of the present invention, the present invention provides a local oscillation phase noise cancellation circuit, including: the device comprises a first frequency mixer, a second frequency mixer, a local oscillator signal source and a subtractor;
local oscillation signals output by the local oscillation signal source are respectively input to local oscillation signal input ends of the first frequency mixer and the second frequency mixer;
a radio frequency input end of the first mixer receives a radio frequency input signal;
the radio frequency input end of the second mixer is connected with a load;
signals output by the output ends of the first frequency mixer and the second frequency mixer are accessed into a phase reducer, and after local oscillation phase noise cancellation is carried out on signals at the two output ends of the first frequency mixer and the second frequency mixer through the phase reducer, output signals of the phase reducer are output as intermediate frequency signals.
Furthermore, an amplitude adjusting circuit is arranged in the subtractor, and the amplitude adjusting circuit is configured to adjust the amplitude of the local oscillator phase noise signal output by the second frequency mixer, so that the amplitude of the local oscillator phase noise signal output by the output end of the second frequency mixer is equal to the amplitude of the local oscillator phase noise signal output by the output end of the first frequency mixer, and the local oscillator phase noise output by the output end of the first frequency mixer is offset.
Further, the circuit further comprises: one end of the first isolator receives the local oscillation signal, and the other end of the first isolator is connected to a local oscillation signal input end of the first frequency mixer; and
and one end of the second isolator receives the local oscillation signal, and the other end of the second isolator is connected to the local oscillation signal input end of the second frequency mixer.
Further, the circuit further comprises: and the power divider is used for dividing the local oscillation signals output by the local oscillation signal source into two paths, and respectively accessing the input ends of the local oscillation signals of the first frequency mixer and the second frequency mixer.
Further, the circuit further comprises: the directional coupler is used for dividing local oscillation signals output by the local oscillation signal source into two paths, an output signal of a main arm of the directional coupler is connected to a local oscillation signal input end of the first frequency mixer, and an output signal of a side arm of the directional coupler is connected to an input end of the amplifier; and
and the amplifier is used for amplifying the output signal of the side arm of the directional coupler, and the output end of the amplifier is connected with the local oscillator signal input end of the second frequency mixer.
The local oscillator phase noise cancellation circuit provided by the invention comprises two mixers, wherein a first mixer is used as a main working mixer (main mixer), the radio frequency input end of the first mixer is connected with a radio frequency input signal, the radio frequency input end of a second mixer is connected with a load, a local oscillator signal source is respectively connected with the local oscillator signal input ends of the first mixer and the second mixer, the intermediate frequency output ends of the first mixer and the second mixer are respectively connected with a phase reducer, and local oscillator phase noise contained in an output signal of the first mixer is cancelled through the phase reducer. The invention can improve the quality of the output signal of the first mixer and improve the linearity and the sensitivity of the output signal of the mixer when small signals are input.
Drawings
FIG. 1A is a circuit schematic of a double balanced mixer;
FIG. 1B is a schematic diagram of a circuit in which a double balanced mixer operates at the positive half cycle of a local oscillator signal;
FIG. 1C is a schematic diagram of a circuit in which a double balanced mixer operates at the negative half cycle of a local oscillator signal;
fig. 2 is a schematic diagram of a principle structure of a local oscillator signal cancellation circuit according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a schematic structural diagram of a subtraction circuit in a local oscillator signal cancellation circuit according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a schematic circuit structure of a local oscillator signal cancellation circuit with an isolator according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a schematic circuit structure of a local oscillator signal cancellation circuit of a power divider according to an embodiment of the present invention;
fig. 6 is a schematic diagram of a schematic circuit structure of a local oscillator signal cancellation circuit using a directional coupler according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the solutions of the present application are further described in detail below with reference to the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
It is to be understood that although the terms first, second, third, etc. may be used herein to describe various information, such information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the present application. The word "if" as used herein may be interpreted as "at … …" or "when … …" or "in response to a determination", depending on the context.
Referring to fig. 1A-1C, fig. 1A is a circuit of a mixer, and fig. 1B and 1C are circuits of a mixer operating in a positive half cycle and a negative half cycle of a local oscillation signal, respectively.
The current and voltage I-V characteristics of the diode can be represented by formula (1)
i＝a0+a1u+a2u2(1)
The higher order terms are ignored in the equation because the higher order term signals generated after mixing can be filtered out after passing through a low pass filter. For the local oscillator positive half cycle, the voltage signals on the two diodes D1 and D3 are
In the formula u0、usRespectively local oscillator signals and radio frequency signals. The current signals of the diodes D1 and D3 are
The intermediate frequency end of the mixer outputs a signal of
Wherein (a)d1-1+ad3-1)≈2a1；(ad1-2+ad3-2)≈2a2. For the ideal case, the I-V characteristics of diodes D1 and D2 are the same, and the D1 and D2 path paths are of equal length; the centre tap of the coil being at the centre position, etc., in which case there is a0＝0，Δa1＝0，Δa2The double balanced mixer intermediate frequency output contains only the difference frequency (omega) except the radio frequency signal (F ═ 0)0-ωs) And sum frequency (ω)0+ωs) Item, i.e.
Actual mixers not being ideal devices, Δ a0，Δa1，Δa2Are all non-zero, resulting in a local oscillator phase noise signal at the intermediate frequency output of the mixer. Commercial mixers give isolation of the local oscillator from the intermediate frequency and local oscillator from the radio frequency, typically 20dB to 30dB, if Δ a is used1Representing all undesired components, let Δ a1Is-25 dB; 2a of2The frequency conversion loss is generally about 6 dB.
When the local oscillator has an interference signal e near the carrier0When the intermediate frequency of the mixer is output as
As shown in the formula (6), the output of the intermediate frequency end of the mixer contains intermediate frequency, local oscillator, radio frequency, and radio frequency and local oscillator frequency and terms, and after passing through the low pass filter, only 4R is reservedLa2u0usAnd 2RLΔa2u0e0Generating intermediate frequency terms
And
suppose a conversion loss of 2a2About-6 dB; Δ a2≈Δa1I.e. Δ a2Also-25 dB, then Δ a2Ratio 2a2Low 19dB, when e0Equal to the signal at the RF input of the mixer, e0The maximum error introduced to the measurement of the intermediate frequency signal is 11%, the maximum error being e0The maximum error is introduced in phase or anti-phase with the rf signal, and becomes smaller in the other phases. Crosstalk signal e0The effect on the measurement can be represented by the formula (7)
In the formula, Pn、PsThe level of the spur signal and the measured intermediate frequency signal at the mixer intermediate frequency output are defined separately. As can be seen from equation (7), when the amplitude of the radio frequency signal becomes smaller, the influence of the interference signal on the intermediate frequency signal output by the mixer becomes larger.
Based on the above analysis, since the mixer cannot achieve ideal double balance and the non-single spectral line of the local oscillator signal spectrum causes self-mixing of the mixer, the local oscillator phase noise signal is output at the intermediate frequency output end of the mixer under the condition that no input is provided at the radio frequency input end. In order to suppress the influence of local oscillation phase noise on the intermediate frequency signal output by the mixer and improve the linearity and sensitivity when small signals are received or measured by the mixer, the invention provides a local oscillation phase noise cancellation method and a local oscillation phase noise cancellation circuit, referring to the circuit structure diagram of fig. 2, the circuit comprises a local oscillation signal source LO, a first mixer M1, a second mixer M2 and a subtractor S, the method comprises the following steps:
step 100, dividing a local oscillation signal output by a local oscillation signal source LO into two paths, and respectively accessing the two paths of local oscillation signals to a first mixer M1 and a second mixer M2;
step 102, using the first mixer M1 as a main working mixer, and receiving a radio frequency input signal RF at a radio frequency input end thereof;
step 104, using the second mixer M2 as an auxiliary mixer for local oscillation phase noise cancellation, wherein the radio frequency input end of the auxiliary mixer is connected with a LOAD;
and step 106, after the intermediate frequency signals output by the two mixers of the first mixer M1 and the second mixer M2 are subjected to local oscillation phase noise cancellation by the subtractor S, taking the output signal of the subtractor as an intermediate frequency output signal.
Referring to fig. 2, the local oscillation phase noise cancellation circuit provided by the present invention includes two mixers, wherein the first mixer is used as an active working mixer, whose rf input end is used to receive an external rf input signal to be processed, and the second mixer is used to cancel local oscillation phase noise included in an output signal of the first mixer, and the rf input end of the second mixer is connected to a load. Based on the foregoing analysis of the self-mixing principle of mixers, both mixers contain local oscillator phase noise generated by self-mixing 
The output of the second mixer is used for offsetting the related local oscillation phase noise contained in the output signal of the first mixer, thereby improving the quality of the intermediate frequency output signal of the first mixer and improving the linearity and sensitivity of the output signal of the mixer when small signals are input.
In an embodiment of the present invention, the subtractor is implemented by using a circuit structure as shown in fig. 3, in which a high-precision operational amplifier is used to implement cancellation processing of local oscillation phase noise in two paths of signals output by two mixers, output signals of the two mixers may be respectively connected to non-inverting and inverting input terminals or inverting and non-inverting input terminals of the operational amplifier according to an application scenario, and an output of the operational amplifier is output as an output signal of the subtractor.
Furthermore, because the two mixers have a difference in balance performance, the local oscillation phase noise contained in the output signals of the two mixers also has an amplitude difference, in order to further reduce the influence of the local oscillation phase noise, in the embodiment of the present invention, an amplitude adjustment circuit is added in the subtractor, in the circuit, the output end of the first mixer, i.e., the main working mixer, is connected to the inverting input end of the operational amplifier, and the output end of the second mixer, i.e., the cancellation auxiliary mixer, is connected to the non-inverting input end of the operational amplifier through an adjustable potentiometer. The adjustable potentiometer in this embodiment is used to adjust the amplitude of the signal, so that the amplitudes of the two local oscillation phase noise signals input to the operational amplifier are equal, thereby achieving the purpose of accurately canceling the local oscillation phase noise contained in the output signal of the first mixer.
In order to prevent crosstalk from being formed after radio frequency signals pass through the mixers, in the embodiment of the present invention, please refer to fig. 4 for example, a first isolator ISO1 is added between the first mixer M1 and the local oscillation signal source LO, and a second isolator ISO2 is added between the second mixer M2 and the local oscillation signal source LO.
In the embodiment of the present invention, please refer to fig. 5 for example, a local oscillator signal is divided into two parts by a power divider DIV, two output signals of the power divider DIV are respectively input to input ends of a first mixer M1 and a second mixer M2, where the power divider is added to divide the local oscillator signal into two parts, and when the level amplitude of the local oscillator signal is limited, a directional coupler may be selected as the power divider because the local oscillator signal is not sufficiently driven after being attenuated by the power divider.
In an embodiment of the present invention, a signal input to the first mixer is a millimeter wave frequency band greater than 50GHz, a local oscillation signal has a limited level amplitude, and is not enough to drive the mixer after being attenuated by the power divider, so a 10dB directional coupler is adopted, as shown in fig. 6, a main arm of the directional coupler CUP is input to the first mixer M1, a side arm of the 10dB directional coupler CUP is output to the second mixer M2 through the millimeter wave amplifier AMP, a radio frequency input of the second mixer M2 is connected to a waveguide LOAD, and a principle of cancellation of local oscillation phase noise refers to the above analysis process, which is not described herein again. Because the phase noise output by the frequency mixer is only a function of the correlation between the local oscillator carrier and the phase noise, although the paths of the local oscillators are different and the electrical lengths are different, the correlation of intermediate frequency output of the two frequency mixers is not influenced.
Since the amplitude of the local oscillator phase noise (i.e. the output signal after the noise is superimposed on the mixing signal) output by the mixer is small, and it is inconvenient to observe whether the local oscillator phase noise is completely cancelled, in combination with the aforementioned example of fig. 3, in order to adjust the subtractor circuit to make the amplitudes of the two outputs equal, and achieve the purpose of cancelling the local oscillator phase noise output by the measuring mixer, the amplitude adjustment circuit in the subtractor can be adjusted by adopting the following means: and under the state that the radio frequency input of the first frequency mixer is turned off, setting the local oscillation signal source to be amplitude modulation output, setting the frequency of the modulation signal to be required intermediate frequency, wherein the modulation depth is 0.5 percent, and at the moment, the output signal of the frequency mixer is larger, and adjusting the phase reducer circuit under the large signal state to ensure that the output of the phase reducer circuit is minimum. After the adjustment is completed, the local oscillator closes the modulation, and the continuous wave output is recovered.
Through actual circuit test, the local oscillator phase noise cancellation method and the local oscillator phase noise cancellation circuit provided by the invention can improve the intermediate frequency output phase noise of the frequency mixer by more than 20dB, and improve the linearity and the sensitivity of small signal measurement. The local oscillator phase noise cancellation method provided by the invention can be used for receiver and radar design, and improves the linearity and sensitivity of small signals to be measured; the method can also be used for a signal analysis and measurement device to reduce the influence of local oscillation phase noise; the method can also be used for a phase noise measuring device to reduce the influence of the introduction of local oscillation phase noise.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A local oscillator phase noise cancellation method is characterized by comprising the following steps:
the local oscillation signal output by the local oscillation signal source is divided into two paths and respectively accessed to a first frequency mixer and a second frequency mixer, and the first frequency mixer and the second frequency mixer are double-balanced frequency mixers;
the first frequency mixer is used as a main working frequency mixer, and a radio frequency input end of the first frequency mixer receives a radio frequency input signal;
the second mixer is used as an auxiliary mixer for offsetting local oscillation phase noise, and the radio frequency input end of the second mixer is connected with a load;
after signals at two output ends of the first frequency mixer and the second frequency mixer are subjected to local oscillation phase noise cancellation by the phase subtracter, the output signal of the phase subtracter is output as an intermediate frequency output signal;
and the phase subtracter is internally provided with an amplitude adjusting circuit which is used for adjusting the amplitude of the local oscillator phase noise signal output by the second frequency mixer, so that the amplitude of the local oscillator phase noise signal output by the output end of the second frequency mixer is equal to the amplitude of the local oscillator phase noise signal output by the output end of the first frequency mixer, and the local oscillator phase noise output by the output end of the first frequency mixer is offset.
2. The method of claim 1, wherein a first isolator is added between the first mixer and the local oscillator signal source and a second isolator is added between the second mixer and the local oscillator signal source to reduce crosstalk of the radio frequency signal.
3. The method according to claim 1 or 2, characterized in that the local oscillator signal output by the local oscillator signal source is divided into two paths by the power divider, and the two paths are respectively connected to the input ends of the local oscillator signals of the first mixer and the second mixer.
4. A method as claimed in claim 1 or 2, characterized in that the local oscillator signal output by the local oscillator signal source is divided into two paths by means of a directional coupler, the main arm of which is input to the first mixer and the output signal of the side arm of which is input to the second mixer via an amplifier.
5. A local oscillator phase noise cancellation circuit, comprising: the device comprises a first frequency mixer, a second frequency mixer, a local oscillator signal source and a subtractor;
local oscillation signals output by a local oscillation signal source are respectively input to local oscillation signal input ends of a first frequency mixer and a second frequency mixer, and the first frequency mixer and the second frequency mixer are double-balanced frequency mixers;
a radio frequency input end of the first mixer receives a radio frequency input signal;
the radio frequency input end of the second mixer is connected with a load;
signals output by the output ends of the first frequency mixer and the second frequency mixer are accessed into a phase reducer, and after local oscillation phase noise cancellation is carried out on the signals at the two output ends of the first frequency mixer and the second frequency mixer through the phase reducer, the output signals of the phase reducer are output as intermediate frequency signals;
and the phase subtracter is internally provided with an amplitude adjusting circuit which is used for adjusting the amplitude of the local oscillator phase noise signal output by the second frequency mixer, so that the amplitude of the local oscillator phase noise signal output by the output end of the second frequency mixer is equal to the amplitude of the local oscillator phase noise signal output by the output end of the first frequency mixer, and the local oscillator phase noise output by the output end of the first frequency mixer is offset.
6. The circuit of claim 5, wherein the circuit further comprises:
one end of the first isolator receives the local oscillation signal, and the other end of the first isolator is connected to a local oscillation signal input end of the first frequency mixer;
and one end of the second isolator receives the local oscillation signal, and the other end of the second isolator is connected to the local oscillation signal input end of the second frequency mixer.
7. The circuit of claim 5 or 6, further comprising:
and the power divider is used for dividing the local oscillation signals output by the local oscillation signal source into two paths, and respectively accessing the input ends of the local oscillation signals of the first frequency mixer and the second frequency mixer.
8. The circuit of claim 5 or 6, further comprising:
the directional coupler is used for dividing local oscillation signals output by the local oscillation signal source into two paths, an output signal of a main arm of the directional coupler is connected to a local oscillation signal input end of the first frequency mixer, and an output signal of a side arm of the directional coupler is connected to an input end of the amplifier;
and the amplifier is used for amplifying the output signal of the side arm of the directional coupler, and the output end of the amplifier is connected with the local oscillator signal input end of the second frequency mixer.
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| US11265034B1 (en) * | 2020-08-07 | 2022-03-01 | Hangzhou Geo-Chip Technology Co., Ltd. | Signal mixing circuit device and receiver |
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| US6785518B2 (en) * | 2001-02-16 | 2004-08-31 | Analog Devices, Inc. | Transmitter and receiver circuit for radio frequency signals |
| CN104168234A (en) * | 2013-05-16 | 2014-11-26 | 中兴通讯股份有限公司 | Signal cancelling method and apparatus of wireless communication system |
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| US6785518B2 (en) * | 2001-02-16 | 2004-08-31 | Analog Devices, Inc. | Transmitter and receiver circuit for radio frequency signals |
| CN104168234A (en) * | 2013-05-16 | 2014-11-26 | 中兴通讯股份有限公司 | Signal cancelling method and apparatus of wireless communication system |
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