System and method suitable for signal source to suppress mirror signal and local oscillator leakage

Abstract

The invention relates to a system suitable for a signal source to realize mirror image signal and local oscillator leakage suppression, which comprises a baseband digital-to-analog converter, an I-path mixer, a Q-path mixer, a filter and a power amplifier, the baseband digital-to-analog converter respectively outputs an I-path signal and a Q-path signal, the I-path mixer receives the I-path signal, the Q-path mixer receives the Q-path signal, and the power amplifier outputs the Q-path signal. And the filter filters output signals of the I-path mixer and the Q-path mixer and outputs the filtered output signals to the power amplifier. The invention further relates to a method for suppressing the signal source mirror image signal and the local oscillator leakage condition. By adopting the system and the method suitable for the signal source to suppress the leakage of the mirror image signal and the local oscillator, the transmission of the signal is optimized when a circuit is designed, and the leakage and the mirror image of the local oscillator signal are suppressed by using a complex frequency mixing architecture, so that the cost can be reduced when a post-stage filter is selected, and the selection becomes easy.

Description

Technical Field

[0001] This invention relates to the field of instrumentation, and more particularly to the field of suppressing image signals and local oscillator leakage in vector signal sources. Specifically, it refers to a system and method for suppressing image signals and local oscillator leakage in signal sources. Background Technology

[0002] In the field of instrumentation, a simplified process for a vector signal source to generate a vector signal is as follows: Figure 1 As shown, the baseband transmits the analog IQ signal generated by the DAC to the modulator for mixing with the local oscillator, and then amplifies the carrier signal before outputting it. During this process, due to the imperfect balance between the phase and amplitude of the signal to be modulated and the local oscillator signal during mixing, and the DC bias of the IQ signal causing leakage of the local oscillator signal to the output, the output signal becomes distorted, exhibiting a spike in the spectral center and a certain amount of image signal, affecting the quality of the output signal. To avoid this, this signal needs to be suppressed.

[0003] The common solution is to add a filter at the modulator output for filtering. The problem is that when the local oscillator signal is within the signal bandwidth, it cannot be easily filtered out by the filter. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a system and method for suppressing image signals and local oscillator leakage in signal sources that is low in cost, easy to select, and widely applicable.

[0005] To achieve the above objectives, the present invention provides a system and method for suppressing image signals and local oscillator leakage in signal sources, as follows:

[0006] This system, applicable to signal sources for suppressing image signals and local oscillator leakage, is characterized by comprising a baseband digital-to-analog converter (DAC), an I-channel mixer, a Q-channel mixer, a filter, and a power amplifier. The input terminals of the I-channel and Q-channel mixers are connected to the DAC, and their output terminals are connected to the filter. The output terminal of the filter is connected to the power amplifier. The DAC outputs I-channel and Q-channel signals respectively. The I-channel mixer receives the I-channel signal, and the Q-channel mixer receives the Q-channel signal. The filter filters the output signals of the I-channel and Q-channel mixers and outputs them to the power amplifier.

[0007] Preferably, the system further comprises a first capacitor and a second capacitor, the first capacitor is connected between the baseband digital-to-analog converter and the I mixer, the second capacitor is connected between the baseband digital-to-analog converter and the Q mixer, the I signal output by the first capacitor and the Q signal output by the second capacitor have the same amplitude and a phase difference of 180°.

[0008] Preferably, the system further comprises a local oscillator unit, the output end of the local oscillator unit is connected with the I mixer and the Q mixer, and the local oscillator unit outputs a local oscillator signal to the I mixer and the Q mixer.

[0009] The method for suppressing the image signal and the local oscillator leakage of the signal source based on the above system mainly comprises the following steps.

[0010] (1) optimizing the differential lines of the IQ signals in the circuit;

[0011] (2) using the complex mixing architecture to mix the IQ signals to generate two signals with the same amplitude and a phase difference of 180°;

[0012] (3) improving the port standing wave of the front end of the IQ input signal of the mixing architecture;

[0013] (4) outputting the signals while eliminating the image signals, making the two pairs of differential lines of the IQ signals equal in length, and optimizing the line length according to the specific frequency.

[0014] The system and the method for suppressing the image signal and the local oscillator leakage of the signal source based on the above system can optimize the transmission of the signals during the design of the circuit and suppress the leakage and the image of the local oscillator signal by using the complex mixing architecture, so that the cost can be reduced when selecting the later filter, and the selection becomes easy. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The signal generation process of the prior art signal source.

[0016] Figure 2 The complex mixing architecture of the system for suppressing the image signal and the local oscillator leakage of the signal source.

[0017] Figure 3 The simultaneous input of the I signal and the Q signal of the system for suppressing the image signal and the local oscillator leakage of the signal source.

[0018] Figure 4 The basic architecture of the system for suppressing the image signal and the local oscillator leakage of the signal source. DETAILED DESCRIPTION

[0019] To more clearly describe the technical content of the present invention, the following description is provided in conjunction with specific embodiments.

[0020] This invention relates to a system for suppressing image signals and local oscillator leakage in a signal source. The system includes a baseband digital-to-analog converter (DAC), an I-channel mixer, a Q-channel mixer, a filter, and a power amplifier. The input terminals of the I-channel and Q-channel mixers are connected to the DAC. The output terminals of the I-channel and Q-channel mixers are connected to the filter. The output terminal of the filter is connected to the power amplifier. The DAC outputs I-channel and Q-channel signals respectively. The I-channel mixer receives the I-channel signal, and the Q-channel mixer receives the Q-channel signal. The filter filters the output signals of the I-channel and Q-channel mixers and outputs them to the power amplifier.

[0021] In a preferred embodiment of the present invention, the system further includes a first capacitor and a second capacitor. The first capacitor is connected between the baseband digital-to-analog converter and the I-channel mixer, and the second capacitor is connected between the baseband digital-to-analog converter and the Q-channel mixer. The I-channel signal output by the first capacitor and the Q-channel signal output by the second capacitor have the same amplitude and a phase difference of 180°.

[0022] In a preferred embodiment of the present invention, the system further includes a local oscillator unit, the output of which is connected to the I-channel mixer and the Q-channel mixer, and the local oscillator unit outputs a local oscillator signal to the I-channel mixer and the Q-channel mixer.

[0023] The method for suppressing signal source image signal and local oscillator leakage based on the above system is characterized by the following steps:

[0024] (1) Optimize the differential lines of the IQ signals in the circuit;

[0025] (2) The IQ signal is mixed using a complex mixing architecture to generate two signals with the same amplitude and a phase difference of 180° and then mixed and superimposed.

[0026] (3) Improve port standing wave ratio at the front end of the IQ input signal of the mixer architecture;

[0027] (4) Output signal, and simultaneously eliminate image, making the two pairs of differential lines of I and Q equal in length, and optimizing the line length according to a specific frequency. In a specific embodiment of the present invention, in order to solve the problem of high pressure on the selection of the modulated filter in the prior art, a method for suppressing image signal and local oscillator leakage during IQ signal modulation is provided. When designing the circuit, the signal transmission is optimized and a complex mixing architecture is used to suppress leakage and image of the local oscillator signal.

[0028] When modulating, the IQ signal and the local signal can be built into the following mathematical formula:

[0029]

[0030] Q(t)=sinωt;

[0031] f Lo_ I(t)=Acos(ω c +θ)+E;

[0032] f LO_ Q(t)=sinω c t;

[0033] Wherein G, D is the amplitude ratio, the phase difference and the relative offset in direct current between the IQ signals, A, θ, E are the amplitude ratio, the phase difference and the relative offset in direct current of the local signal on the IQ.

[0034] And the following modulation signal output formula is combined:

[0035] f o (t)=I(t)×f LO_ I(t)-Q(t)×f LO_ Q(t);

[0036] The local oscillator leakage is obtained:

[0037] f c (t)=DAcos(ω C t+θ);

[0038] It can be known that the leakage of the local oscillator is caused by the direct current offset between the IQ signals.

[0039] Therefore, firstly, the differential line of the IQ signal in the circuit is optimized, and the AC coupling mode is adopted to eliminate the direct current error and common mode interference between the two signals and reduce the influence of the leakage.

[0040] Secondly, the complex mixing architecture is used to mix the IQ signal, so that a signal that can offset the local oscillator leakage is generated, and the required signal is output while the image is eliminated, and this step is the main step.

[0041] It can be known that the main steps of the method for suppressing the signal source image signal and the local oscillator leakage are as follows:

[0042] (1) the differential line of the IQ signal in the circuit is optimized: the equal length error of the line is ensured to be as small as possible, and is ensured to be within 1mil; the width, the spacing of the line are optimized, and the integrity of the differential signal transmission is ensured;

[0043] (2) The IQ signal is mixed using a complex mixing architecture to generate two signals with the same amplitude and a phase difference of 180°, which are mixed and superimposed to cause the local oscillator leakage to cancel each other out.

[0044] (3) Improve the port standing wave at the front end of the IQ input signal of the mixer architecture, ensure the phase continuity and integrity of the broadband signal, and help cancel the leakage of the local oscillator;

[0045] (4) Output signal, while eliminating image. Ensure that the two pairs of differential lines (I and Q) are of equal length. Optimize the line length according to a specific frequency to ensure that the intersecting phases match during I and Q mixing and superposition, thereby eliminating the image signal. Figure 2 shows the architecture of complex mixing. Figure 3 As shown, when the I and Q signals are simultaneously input with the same signal and a 90° phase difference, the signal obtained by adding the local oscillator frequency to the input frequency has an upper sideband signal with the same phase, while the difference between the two is out of phase. In this case, the sideband signal on one side is eliminated without any filtering. To completely eliminate the image problem, the output amplitude of this part must be exactly the same and the phase difference must be precisely 180°, which is quite troublesome in practice. However, for the previous design, most of the unwanted signals have been eliminated, and then a filter is added after mixing. At this time, the requirements for the filter can be reduced, making it easier to implement. The basic structure is as follows. Figure 4 As shown.

[0046] For the specific implementation scheme of this embodiment, please refer to the relevant descriptions in the above embodiments, which will not be repeated here.

[0047] It is understood that the same or similar parts in the above embodiments can be referred to each other, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0048] It should be noted that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means at least two.

[0049] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0050] The system and method for suppressing image signals and local oscillator leakage suitable for signal source are adopted, the transmission of signals is optimized when the circuit is designed, the leakage and image of the local oscillator are suppressed by using the architecture of complex mixing, so that the cost can be reduced when the later filter is selected, and it becomes easy to select.

[0051] In this specification, the application has been described with reference to its particular embodiments. It is clear, however, that various modifications and changes can be made without departing from the spirit and scope of the application. Therefore, the specification and drawings should be considered as illustrative and not restrictive.

Claims

1. A system suitable for a signal source to implement rejection of image signals and local oscillator leakage, characterized in that, The system comprises a baseband digital-to-analog converter, an I-path mixer, a Q-path mixer, a filter and a power amplifier, the input ends of the I-path mixer and the Q-path mixer are connected with the baseband digital-to-analog converter, the output ends of the I-path mixer and the Q-path mixer are connected with the filter, the output end of the filter is connected with the power amplifier, the baseband digital-to-analog converter outputs an I-path signal and a Q-path signal respectively, the I-path mixer receives the I-path signal, the Q-path mixer receives the Q-path signal, the filter filters the output signals of the I-path mixer and the Q-path mixer and outputs to the power amplifier.

2. The system for rejecting image signals and LO leakage for a signal source implementation as claimed in claim 1, wherein, The system further comprises a first capacitor and a second capacitor, the first capacitor is connected between the baseband digital-to-analog converter and the I-path mixer, the second capacitor is connected between the baseband digital-to-analog converter and the Q-path mixer, the amplitudes of the I-path signal output by the first capacitor and the Q-path signal output by the second capacitor are consistent and the phase difference is 180°.

3. The system for rejecting image signals and LO leakage for a signal source implementation as claimed in claim 1, wherein, The system further comprises a local oscillator unit, the output end of which is connected with the I-path mixer and the Q-path mixer, the local oscillator unit outputs a local oscillator signal to the I-path mixer and the Q-path mixer.

4. A method for suppressing the signal source mirror signal and the local oscillator leakage condition based on the system of claim 1, characterized in that, The method comprises the following steps: (1) optimizing the differential lines of the IQ signals in the circuit; (2) using a complex mixing architecture to mix the IQ signals to generate two paths of signals with consistent amplitudes and a phase difference of 180° for superposition; (3) improving the port standing wave of the front end of the IQ input signal of the mixing architecture; (4) outputting the signal while eliminating the image, making the two pairs of differential lines of the IQ equal in length and optimizing the line length according to the specific frequency.

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