Local signal generation circuit and superheterodyne receiver

Abstract

The application discloses a local oscillator signal generation circuit and a superheterodyne receiver, and belongs to the technical field of superheterodyne receivers. The local oscillator signal generation circuit comprises a first local oscillator circuit and a second local oscillator circuit. In the first local oscillator circuit, a K frequency multiplier multiplies a reference signal by K, a first phase discriminator generates an error signal based on the reference signal and a second mixer output, a first loop filter outputs a tuning voltage to control a first voltage-controlled oscillator to generate an oscillation signal, and a first local oscillator coupler divides the oscillation signal into two paths, one path generates a first local oscillator signal, and the other path mixes a second local oscillator signal output by the second local oscillator circuit to obtain a first mixed signal, the first mixed signal is mixed with a K frequency signal to obtain a second mixed signal and is fed back to the first phase discriminator. The application maps the phase noise of the second local oscillator to the first local oscillator, realizes coherent cancellation in cooperation with the second mixing of the receiver, and significantly reduces the total phase noise of the system without a frequency divider in the feedback path.

Description

Technical Field

[0001] This invention relates to the field of superheterodyne receiver technology, specifically to a local oscillator signal generation circuit and a superheterodyne receiver. Background Technology

[0002] Superheterodyne receivers are one of the most widely used receiver architectures in modern radio communication, offering advantages such as high selectivity, consistent frequency response, and applicability across a wide frequency range. Superheterodyne receivers typically employ two or three mixing stages, progressively down-converting the received high-frequency RF signal to low-frequency intermediate frequency (IF) signals for subsequent demodulation and processing. Each mixing stage requires an independent local oscillator signal. With the continuous development of communication technology, the performance requirements for superheterodyne receivers are constantly increasing, especially phase noise performance, as it directly determines the demodulation accuracy, receiving sensitivity, and anti-interference capability of the superheterodyne receiver. The phase noise of a superheterodyne receiver primarily depends on the phase noise of each local oscillator signal.

[0003] Currently, the industry commonly employs a dual independent phase-locked loop (PLL) architecture based on a common reference signal to generate dual local oscillator (LO) signals. This involves using a single, highly stable reference signal source, splitting it into two paths by a power divider, and then inputting each path into two independent integer-division PLLs. Each PLL consists of a phase detector, loop filter, voltage-controlled oscillator (VCO), coupler, and frequency divider, forming a closed-loop feedback circuit. This circuit multiplies and locks the low-frequency reference signal to the desired LO frequency, which is then amplified and output to the corresponding mixer. Utilizing the coherence of the common reference signal, the derived phase noise from the reference signal source in the two LO signals can be partially canceled out during the frequency subtraction operation of the receiver's second-stage frequency conversion, thereby reducing the overall phase noise of the system to some extent.

[0004] However, the aforementioned dual independent phase-locked loop (PLL) architecture local oscillator signal generation scheme based on a common reference signal has the following drawbacks: First, the integrated phase noise generated by the two independent PLLs and the additional phase noise generated by the two independent local oscillator amplifiers are both incoherent phase noises. These two types of phase noise cannot be eliminated by coherent cancellation mechanisms and can only be directly superimposed on the total phase noise of the system. Second, both independent PLLs use frequency dividers to achieve phase locking and output frequency multiplication. However, frequency dividers are active digital devices, which introduce various incoherent phase noises such as power supply noise, switching noise, and flicker noise, further raising the system's phase noise floor. Third, to achieve good phase noise performance, the traditional dual independent PLL architecture based on a common reference signal requires the selection of high-performance components, which undoubtedly increases the hardware cost of the system. Summary of the Invention

[0005] This application provides a local oscillator signal generation circuit and a superheterodyne receiver to solve the problems of existing local oscillator signal generation schemes based on dual independent phase-locked loop architecture with the same source reference signal, which cannot achieve the cancellation of incoherent phase noise and introduce more incoherent noise when using a frequency divider.

[0006] According to a first aspect, one embodiment provides a local oscillator signal generation circuit, characterized in that it includes a first local oscillator circuit and a second local oscillator circuit, wherein the first local oscillator circuit is used to generate a first local oscillator signal based on a reference signal, and the second local oscillator circuit is used to generate a second local oscillator signal based on the reference signal; wherein:

[0007] The first local oscillator circuit includes a first phase detector, a first loop filter, a first voltage-controlled oscillator, a first local oscillator coupler, a first mixer, a second mixer, and a K-multiplier.

[0008] The K-frequency multiplier is used to multiply the reference signal by K to obtain a K-frequency signal;

[0009] The first phase detector is used to generate an error signal based on the reference signal and the signal output by the second mixer;

[0010] The first loop filter is used to generate a tuned voltage signal based on the error signal;

[0011] The first voltage-controlled oscillator is used to generate an oscillation signal based on the tuning voltage signal;

[0012] The first local oscillator coupler is used to generate and output a first oscillator signal and a second oscillator signal based on the oscillator signal, wherein the first oscillator signal is used to generate the first local oscillator signal;

[0013] The first mixer is used to generate a first mixed signal based on the second oscillation signal and the second local oscillator signal;

[0014] The second mixer is used to generate a second mixed signal based on the first mixed signal and the K-fold frequency signal and output it to the first phase detector.

[0015] In one embodiment, the frequency f of the first local oscillator signal LO1 The frequency f of the reference signal ref and the frequency f of the second local oscillator signal LO2 Satisfy: f LO1 = (K+1) × f ref + f LO2 .

[0016] In one embodiment, the first local oscillator circuit further includes:

[0017] A first intermediate frequency filter is used to filter the first mixing signal before the second mixer generates the second mixing signal based on the first mixing signal and the K-fold frequency signal, so that the second mixer generates the second mixing signal based on the K-fold frequency signal and the filtered first mixing signal.

[0018] In one embodiment, the first local oscillator circuit further includes:

[0019] The second intermediate frequency filter is used to filter the second mixing signal before the second mixer outputs the second mixing signal to the first phase detector, so as to output the filtered second mixing signal to the first phase detector.

[0020] In one embodiment, the first local oscillator circuit further includes:

[0021] The first local oscillator amplifier is used to amplify the power of the first oscillation signal to obtain the first local oscillator signal.

[0022] In one embodiment, the local oscillator signal generation circuit further includes:

[0023] The first power divider is used to receive the signal output from the reference signal source and split it into three paths, which are respectively used as reference signals for the first phase detector, reference signals for the K frequency multiplier, and reference signals for the second local oscillator circuit.

[0024] In one embodiment, the second local oscillator circuit uses a phase-locked loop based on a frequency divider for phase locking and frequency multiplication to generate the second local oscillator signal.

[0025] In one embodiment, the second local oscillator circuit includes:

[0026] The second power divider is used to split the signal output from the second local oscillator circuit into two paths: one path serves as the second local oscillator signal output from the second local oscillator circuit, and the other path serves as the second local oscillator signal provided to the first mixer.

[0027] In one embodiment, the second local oscillator circuit further includes: a second phase detector, a second loop filter, a second voltage-controlled oscillator, a second local oscillator coupler, and a frequency divider.

[0028] According to a second aspect, one embodiment provides a superheterodyne receiver, including a first-stage mixer unit and a second-stage mixer unit, characterized in that it further includes a local oscillator signal generation circuit as described in any embodiment of the first aspect of this application, wherein:

[0029] The local oscillator signal generation circuit includes a first local oscillator circuit and a second local oscillator circuit;

[0030] The first local oscillator circuit is used to provide the first local oscillator signal required by the first-stage mixer unit;

[0031] The second local oscillator circuit is used to provide the second local oscillator signal required by the secondary mixer unit.

[0032] In one embodiment, the output signal frequency f of the secondary mixer unit is... IF2 The frequency f of the first local oscillator signal LO1 The frequency f of the second local oscillator signal LO2 and the frequency f of the radio frequency received signal RF Satisfy: f IF2 = f LO1 -f RF -f LO2 .

[0033] According to the local oscillator signal generation circuit and superheterodyne receiver of the above embodiments, by setting a first local oscillator circuit and a second local oscillator circuit to generate a first local oscillator signal and a second local oscillator signal based on a reference signal, respectively, the first mixer in the first local oscillator circuit mixes the second oscillation signal from the first voltage-controlled oscillator with the second local oscillator signal to obtain a first mixed signal. The second mixer mixes the first mixed signal with a K-fold frequency signal obtained by multiplying the reference signal by a K-fold frequency multiplier and feeds it back to the first phase detector, thereby forming a feedback structure of the first local oscillator circuit based on "mixer + frequency multiplier". The phase noise of the second local oscillator signal is accurately mapped and embedded into the first local oscillator signal, so that the first local oscillator signal and the second local oscillator signal have noise coherence at the second-stage mixing node of the receiver. Then, at this node, through the subtraction operation relationship of the second-stage mixing of the receiver, all phase noise, including incoherent noise in the second local oscillator signal, is completely canceled, thereby significantly improving the overall phase noise performance of the receiver system. Meanwhile, since the feedback path of the first local oscillator circuit does not use the frequency divider required by a traditional phase-locked loop, it avoids the incoherent noise such as power supply noise and switching noise introduced by the frequency divider as an active digital device, further reducing the system's phase noise floor. Furthermore, since the phase noise of the second local oscillator signal can be completely canceled and is independent of the specific structure of the second local oscillator circuit, the second local oscillator circuit only needs to use the most basic local oscillator signal generation scheme. Moreover, it can be built using lower-specification and lower-priced components, thereby effectively reducing the overall cost of the receiver system. Attached Figure Description

[0034] Figure 1 This is a block diagram of a superheterodyne receiver architecture employing a two-stage mixing scheme, according to one embodiment.

[0035] Figure 2 This is an example diagram of a local oscillator signal generation scheme based on a dual independent phase-locked loop architecture with a common reference signal, according to one embodiment.

[0036] Figure 3 This is a schematic diagram of the structure of a local oscillator signal generation circuit according to one embodiment;

[0037] Figure 4 This is a structural example diagram of a second local oscillator circuit according to one embodiment;

[0038] Figure 5 This is a structural example diagram of a local oscillator signal generation circuit according to one embodiment;

[0039] Figure 6 This is a schematic diagram of the structure of a superheterodyne receiver according to one embodiment. Detailed Implementation

[0040] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments. Similar elements in different embodiments are referred to by related similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the present application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to the present application are not shown or described in the specification. This is to avoid obscuring the core parts of the present application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0041] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for the clear description of a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0042] The serial numbers assigned to components in this document, such as "first" and "second," are used only to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages).

[0043] As is understandable, the basic working principle of a superheterodyne receiver is to use a mixer to convert the radio frequency signal and the local oscillator signal to a fixed intermediate frequency signal. Please refer to [link / reference needed]. Figure 1 Some embodiments provide block diagrams of existing superheterodyne receiver architectures employing a two-stage mixing scheme. For example... Figure 1The superheterodyne receiver architecture shown has the following steps: the wideband input signal passes through an attenuator and a pre-filter, and is then mixed with the first local oscillator in a mixer to obtain the first intermediate frequency (IF) signal. The first IF signal passes through an IF amplifier and an IF filter, and is then mixed with the second local oscillator in a mixer to obtain the second IF signal. The second IF signal then passes through a second IF amplifier and a second IF filter before reaching the analog-to-digital converter (ADC) for analog-to-digital conversion.

[0044] In the above process, the phase noise of the local oscillator signal is directly superimposed on the intermediate frequency signal through the nonlinear frequency transformation of the mixer. If the phase noise of the receiver's local oscillator signal is poor, even if the transmitter's phase noise control is excellent, resulting in a relatively low phase noise of the received radio frequency signal, the phase noise of the system will still be degraded due to the superposition of the local oscillator signal's phase noise on the receiver's intermediate frequency signal.

[0045] Please refer to Figure 2 Some embodiments provide a local oscillator signal generation scheme based on a dual independent phase-locked loop (PLL) architecture with a common reference signal. The integrated phase noise of the PLL can be understood as the sum of phase noise generated by each independent component within the PLL, independent of the reference signal source (unless otherwise specified, "integrated phase noise of the PLL" in this application is understood in this way). Figure 2 In the dual independent phase-locked loop (PLL) architecture shown, even using identical reference sources, the voltage-controlled oscillator, frequency divider, and phase detector of each of the two PLLs are completely independent physical components, and the phase noise they generate is also independent and uncorrelated in the time domain. That is, in the "integrated phase noise" of the two PLLs, the noise components generated by all the independent components are uncorrelated; therefore, the "integrated phase noise" of the two PLLs belongs to incoherent noise.

[0046] The additional phase noise of a local oscillator amplifier (LOA) can be understood as the noise generated by its active components (such as transistors) when amplifying the local oscillator signal. This noise is modulated onto the phase of the carrier signal as additive noise, causing a fixed amount of degradation in the output phase noise relative to the input signal. This degradation is unrelated to the phase noise of the input signal and is introduced by the amplifier itself. Two independent LOAs (a primary LOA and a secondary LOA) are completely independent RF devices, each with its own power supply, bias circuit, and active transistors. The additional phase noise they introduce arises from two different physical processes. The time-domain waveforms of the noise sources are completely uncorrelated and do not have any fixed phase correlation. Therefore, the additional phase noise of the two LOAs also belongs to incoherent noise.

[0047] According to the principle of noise power superposition, incoherent noise energy is directly added on the spectrum (power spectral density is added), which cannot be eliminated by the subtraction operation of the mixer in the receiver stage, thus limiting the lower limit of the system's phase noise performance at the architecture level.

[0048] As an active digital device in the phase-locked loop (PLL) feedback path, the frequency divider inevitably introduces additional phase noise. This noise primarily includes: thermal and flicker noise generated by numerous internal active components (such as transistors, flip-flops, and logic gates); power supply noise coupled into the divider via a shared power line; and switching noise from the high-speed switching of transistors between on and off states. This noise is directly superimposed on the phase noise of the voltage-controlled oscillator (VCO) and shaped into in-band noise through the PLL's closed-loop transfer function. Assuming a division ratio of N, this phase noise from the divider is amplified by a factor of 20log(N), thus directly raising the system's phase noise floor due to the additional phase noise introduced by the divider. Furthermore, in systems requiring wideband coverage or high-frequency output, the division ratio N is often large, making the divider noise one of the main contributors to the system's phase noise.

[0049] Assume the reference signal frequency is f ref The reference signal phase noise is PN. ref The first local oscillator output frequency is f LO1 =M×f ref (M is the division ratio of the first local oscillator), the output frequency of the second local oscillator is f. LO2 =N×f ref (N is the division ratio of the two local oscillator frequency dividers), then the output phase noise of the first local oscillator is PN. LO1 =PN ref ×M 2 +PN PLL1 + PN PA1 The phase noise of the second local oscillator output is PN. LO2 =PN ref × N 2 + PN PLL2 + PN PA2 , where PN ref ×M 2 Phase noise is derived from the reference signal of the local oscillator, PN PLL1 For integrated phase noise of a oscillator phase-locked loop, PN PA1 To provide additional phase noise for a local oscillator amplifier, PN ref ×N 2 Phase noise is derived from the reference signal of the two local oscillators, PN PLL2 For the integrated phase noise of the two local oscillator phase-locked loop, PN PA2 This is the additional phase noise of the dual local oscillator amplifier.

[0050] Taking a superheterodyne receiver employing two-stage frequency conversion as an example, the RF input signal frequency is: f RF The output frequency of the first-stage frequency converter (down-conversion) is f. IF1 = f LO1 – f RF The output frequency of the two-stage frequency converter (down-conversion) is f. IF2 = f IF1 – f LO2 = f LO1 – f RF – f LO2 Therefore, the system phase noise output by the receiver's second-stage frequency conversion node is PN. sys1 =PN ref ×(M - N) 2 +PN PLL1 + PN PLL2 + PN PA1 + PN PA2 Since the reference signals of LO1 and LO2 originate from the same source, PN... ref ×M 2 and PN ref ×N 2 Becoming coherent and able to be in PN sys1 Partial cancellation, PN ref ×(M - N) 2 Phase noise is derived from the reference signal after coherent cancellation; while PN PLL1 PN PA1 PN PLL2 and PN PA2 For incoherent phase noise, in PN sys1 They can only be added together, not canceled out.

[0051] for Figure 2 The local oscillator signal generation scheme based on a dual independent phase-locked loop architecture with a common reference signal, as shown, relies heavily on the "native quality" of individual components for its final phase noise performance. In other words, to achieve better system phase noise performance, the noise contribution of each component must be sufficiently low. Therefore, to meet the target phase noise performance, designers are forced to select high-performance (i.e., low-noise) models for each component, leading to an increase in the overall hardware cost of the system.

[0052] To address the above issues, this application proposes an improved local oscillator (LO) signal generation scheme for the existing dual independent phase-locked loop (PLL) architecture based on a common reference signal. This scheme primarily introduces a component of the second LO signal into the PLL feedback path of the first LO using a mixer. This accurately maps and embeds the phase noise of the second LO signal into the first LO signal, ensuring noise coherence between the two signals at the receiver's secondary mixer node. At this node, a subtraction operation during mixing completely cancels out the phase noise of the second LO signal, significantly improving the overall phase noise performance of the receiver system. Furthermore, by replacing the active frequency divider with a passive frequency multiplier and mixer in the first LO circuit, incoherent noise sources such as power supply noise, switching noise, and flicker noise introduced by the frequency divider are eliminated, reducing the system's phase noise floor.

[0053] Please refer to Figure 3 In some embodiments, a local oscillator signal generation circuit 100 is provided, including a first local oscillator circuit 110 and a second local oscillator circuit 210. The first local oscillator circuit 110 is used to generate a first local oscillator signal based on a reference signal, and the second local oscillator circuit 210 is used to generate a second local oscillator signal based on the reference signal; wherein:

[0054] The first local oscillator circuit 110 includes a first phase detector 111, a first loop filter 112, a first voltage-controlled oscillator 113, a first local oscillator coupler 114, a first mixer 115, a second mixer 116, and a K-multiplier 117.

[0055] K-frequency multiplier 117 is used to multiply the reference signal by K to obtain a K-frequency signal.

[0056] In some embodiments, the input of the K-frequency multiplier 117 is connected to a reference signal source, and the output of the K-frequency multiplier 117 is connected to the second input of the second mixer 116; the frequency f of the K-frequency multiplier signal... K The frequency f of the reference signal ref K times, i.e. f K =K×f ref .

[0057] The first phase detector 111 is used to generate an error signal based on the reference signal and the signal output by the second mixer 116.

[0058] In some embodiments, the first phase detector 111 has a first input terminal and a second input terminal. The first input terminal of the first phase detector 111 is connected to a reference signal source to receive a reference signal; the second input terminal of the first phase detector 111 is connected to the output terminal of the second mixer 116 to receive the signal output by the second mixer 116. The first phase detector 111 is used to compare the phase difference between the reference signal and the second mixed signal, and generates an error signal based on the phase difference. This error signal reflects the phase deviation between the reference signal and the feedback signal, and is the basis of phase-locked loop closed-loop control.

[0059] The first loop filter 112 is used to generate a tuned voltage signal based on the error signal.

[0060] In some embodiments, the input of the first loop filter 112 is connected to the output of the first phase detector 111 to receive an error signal. The first loop filter 112 filters the error signal, removing high-frequency components and noise to generate a smooth tuning voltage signal. This tuning voltage signal is a DC control voltage whose amplitude varies with the phase difference, and is used to control the output frequency of the first voltage-controlled oscillator 113. The first loop filter 112 can be a low-pass filter or a proportional-integral filter.

[0061] The first voltage-controlled oscillator 113 is used to generate an oscillation signal based on the tuning voltage signal.

[0062] In some embodiments, the input of the first voltage-controlled oscillator 113 is connected to the output of the first loop filter 112 to receive a tuning voltage signal. The first voltage-controlled oscillator 113 generates an oscillation signal based on the tuning voltage signal, the frequency of which varies with the tuning voltage. When the phase-locked loop is locked, the frequency of the oscillation signal stabilizes at the target frequency.

[0063] The first local oscillator coupler 114 is used to generate and output a first oscillator signal and a second oscillator signal based on the oscillation signal, wherein the first oscillator signal is used to generate the first local oscillator signal.

[0064] In some embodiments, the input of the first local oscillator coupler 114 is connected to the output of the first voltage-controlled oscillator 113 to receive the oscillation signal. The first local oscillator coupler 114 is used to distribute the power of the oscillation signal into two paths: a first oscillation signal and a second oscillation signal. Specifically, the first output of the first local oscillator coupler 114 outputs the first oscillation signal, which, after further processing (such as amplification and filtering), generates a first local oscillator signal LO1, which is supplied to the mixer of the receiver. The second output of the first local oscillator coupler 114 outputs the second oscillation signal, which is sent to the feedback path to participate in subsequent frequency conversion and phase locking. The first local oscillator coupler 114 can be implemented using devices such as directional couplers or power dividers, and its coupling degree is set according to the actual power requirements, for example, the main output accounts for 80% to 90% of the total power, and the coupled branch accounts for 10% to 20%.

[0065] The first mixer 115 is used to generate a first mixed signal based on the second oscillation signal and the second local oscillator signal.

[0066] In some embodiments, the first mixer 115 has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the first mixer 115 is connected to the second output terminal of the first local oscillator coupler 114 to receive the second oscillation signal; the second input terminal of the first mixer 115 is connected to the output terminal of the second local oscillator circuit 210 to receive the second local oscillator signal LO2. The first mixer 115 is used to mix the second oscillation signal and the second local oscillator signal to generate a first mixed signal. This first mixed signal includes the difference frequency or sum frequency component of the second oscillation signal and the second local oscillator signal. Optionally, the difference frequency component is selected as the useful signal, and its frequency is |f VCO -f LO2 |, where f VCO f is the output frequency of the first voltage-controlled oscillator 113. LO2 The frequency of the second local oscillator signal.

[0067] The second mixer 116 is used to generate a second mixed signal based on the first mixed signal and the K-fold frequency signal and output it to the first phase detector 111.

[0068] In some embodiments, the second mixer 116 has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the second mixer 116 is connected to the output terminal of the first mixer 115 to receive the first mixed signal; the second input terminal of the second mixer 116 is connected to the output terminal of the K-multiplier 117 to receive the K-multiplier signal. The second mixer 116 is used to mix the first mixed signal with the K-multiplier signal to generate a second mixed signal. This second mixed signal includes the difference frequency or sum frequency component of the first mixed signal and the K-multiplier signal. Optionally, the difference frequency component is selected as the useful signal, and its frequency is ||fVCO -f LO2 |- K× f ref The output of the second mixer 116 is connected to the second input of the first phase detector 111, and the second mixing signal is fed back to the first phase detector 111.

[0069] In some embodiments, the frequency f of the first local oscillator signal LO1 The frequency f of the reference signal ref and the frequency f of the second local oscillator signal LO2 Satisfy: f LO1 = (K+1) × f ref + f LO2 .

[0070] It is understandable that when the phase-locked loop is locked, the frequency of the second mixer signal is equal to the frequency f of the reference signal. ref That is, it satisfies the following frequency relationship: ||f VCO -f LO2 | - K× f ref | = f ref Solving this equation (assuming that each stage takes a difference frequency and the positive and negative signs are appropriately chosen), the output frequency of the first voltage-controlled oscillator 113 can be obtained as: f VCO = (K+1)×f ref + f LO2 Since the first local oscillator signal LO1 originates from the oscillation signal of the first voltage-controlled oscillator 113, the first local oscillator frequency f LO1 = f VCO =(K+1)×f ref + f LO2 .

[0071] According to the local oscillator signal generation circuit of the above embodiment, a first local oscillator circuit and a second local oscillator circuit are respectively set to generate a first local oscillator signal and a second local oscillator signal based on a reference signal. The first mixer in the first local oscillator circuit mixes the second oscillation signal from the first voltage-controlled oscillator with the second local oscillator signal to obtain a first mixed signal. The second mixer mixes the first mixed signal with a K-fold frequency signal obtained by multiplying the reference signal by a K-fold frequency multiplier and feeds it back to the first phase detector, thereby forming a feedback structure of "mixer + frequency multiplier" based on the first local oscillator circuit. The phase noise of the second local oscillator signal is accurately mapped and embedded into the first local oscillator signal, so that the first local oscillator signal and the second local oscillator signal have noise coherence at the second-stage mixing node of the receiver. Then, at this node, through the subtraction operation relationship of the second-stage mixing of the receiver, all phase noise, including incoherent noise in the second local oscillator signal, is completely canceled, thereby significantly improving the overall phase noise performance of the receiver system. Meanwhile, since the feedback path of the first local oscillator circuit does not use the frequency divider required by a traditional phase-locked loop, it avoids the incoherent noise such as power supply noise and switching noise introduced by the frequency divider as an active digital device, further reducing the system's phase noise floor. Furthermore, since the phase noise of the second local oscillator signal can be completely canceled and is independent of the specific structure of the second local oscillator circuit, the second local oscillator circuit only needs to use the most basic local oscillator signal generation scheme. Moreover, it can be built using lower-specification and lower-priced components, thereby effectively reducing the overall cost of the receiver system.

[0072] It should be noted that the second local oscillator circuit 210 can adopt a traditional phase-locked loop frequency synthesizer structure, or a direct digital frequency synthesizer or other frequency synthesis schemes, as long as it can generate the required second local oscillator signal based on the reference signal. However, for the purpose of reducing costs, while meeting the basic requirements of the second local oscillator signal, the second local oscillator circuit 210 can adopt a simpler implementation architecture and / or select components with lower performance specifications.

[0073] In some embodiments, the second local oscillator circuit 210 uses a phase-locked loop based on a frequency divider for phase locking and frequency multiplication to generate the second local oscillator signal.

[0074] In some embodiments, the second local oscillator circuit 210 includes a second power divider 211, which is used to divide the signal output by the second local oscillator circuit 210 into two paths, one path as the second local oscillator signal output by the second local oscillator circuit 210, and the other path as the second local oscillator signal provided to the first mixer 115.

[0075] It is understandable that by setting the second power divider 211, the same second local oscillator signal can be supplied to the receiver's secondary mixer node and the feedback path of the first local oscillator circuit 110 simultaneously without adding an additional local oscillator source, and the second local oscillator signals on the two paths are completely from the same source. This is an important guarantee for achieving subsequent coherent cancellation.

[0076] In some embodiments, the second local oscillator circuit 210 further includes: a second phase detector 212, a second loop filter 213, a second voltage-controlled oscillator 214, a second local oscillator coupler 215, and a frequency divider 216.

[0077] In some embodiments, the second local oscillator circuit 210 further includes a second local oscillator amplifier 217 located between the second voltage-controlled oscillator 214 and the second local oscillator coupler 215.

[0078] Please refer to Figure 4Some embodiments provide structural examples of the second local oscillator circuit 210. The first input terminal of the second phase detector 212 is connected to a reference signal source to receive a reference signal; the second input terminal of the second phase detector 212 is connected to the output terminal of the frequency divider 216 to receive the frequency-divided feedback signal. The second phase detector 212 is used to compare the phase difference between the reference signal and the frequency-divided feedback signal and generate a second local oscillator error signal. The input terminal of the second loop filter 213 is connected to the output terminal of the second phase detector 212, and the output terminal of the second loop filter 213 is connected to the input terminal of the second voltage-controlled oscillator 214, used to filter the second local oscillator error signal and generate a second local oscillator tuning voltage. The second voltage-controlled oscillator 214 generates a second local oscillator oscillation signal under the control of the second local oscillator tuning voltage. The input terminal of the second local oscillator coupler 215 is connected to the output terminal of the second voltage-controlled oscillator 214, used to divide the second local oscillator oscillation signal into two paths: one path is output as the main signal to the input terminal of the second local oscillator amplifier 217; the other path is output as a feedback signal to the input terminal of the frequency divider 216. The second local oscillator coupler 215 can be implemented using a directional coupler or a power divider. The output of the frequency divider 216 is connected to the second input of the second phase detector 212, used to divide the high-frequency output of the second voltage-controlled oscillator 214 to a frequency close to the reference signal frequency, so that phase comparison can be performed by the second phase detector 212. The second local oscillator amplifier 217 is used to amplify the main signal of the two local oscillator signals to obtain the second local oscillator signal. The input of the second power divider 211 is connected to the output of the second local oscillator amplifier 217, used to split the second local oscillator signal into two paths. The first output of the second power divider 211 serves as the output port of the second local oscillator signal LO2, providing one path of the second local oscillator signal to the secondary mixer node of the receiver; the second output of the second power divider 211 is connected to the second input of the first mixer 115, providing the other path of the second local oscillator signal to the feedback path of the first local oscillator circuit 110. The frequency of the second local oscillator signal LO2 is f. LO2 =N×f ref , where N is the division ratio of the frequency divider 216.

[0079] Furthermore, in some embodiments, the first local oscillator circuit 110 further includes: a first intermediate frequency filter 118, used to filter the first mixing signal before the second mixer 116 generates the second mixing signal based on the first mixing signal and the K-fold frequency signal, so that the second mixer 116 generates the second mixing signal based on the K-fold frequency signal and the filtered first mixing signal.

[0080] In some embodiments, the first intermediate frequency filter 118 is disposed between the output of the first mixer 115 and the first input of the second mixer 116.

[0081] Understandably, the first mixer 115 will convert the second oscillation signal (frequency f) into a frequency of f. VCO ) and the second local oscillator signal (frequency f) LO2 After mixing, the first mixed signal output simultaneously contains a sum frequency component (frequency f). VCO + f LO2 ) and difference frequency component (frequency of |f VCO -f LO2 In addition, it may also contain intermodulation products of various harmonics. The first intermediate frequency filter 118 is used to filter the first mixing signal before it enters the second mixer 116, and extract the difference frequency component (frequency of |f|). VCO -f LO2 |) serves as a useful first mixing signal, while suppressing sum-frequency components and other spurious signals.

[0082] In some embodiments, the first intermediate frequency filter 118 is implemented using a bandpass filter or a low-pass filter, and the center frequency of the filter is designed to be the first intermediate frequency f. IF1 = |f VCO -f LO2 The filter bandwidth is set according to system requirements.

[0083] Furthermore, in some embodiments, the first local oscillator circuit 110 further includes a second intermediate frequency filter 119, which is used to filter the second mixing signal before the second mixer 116 outputs the second mixing signal to the first phase detector 111, so as to output the filtered second mixing signal to the first phase detector 111.

[0084] In some embodiments, the second intermediate frequency filter 119 is disposed between the output of the second mixer 116 and the second input of the first phase detector 111.

[0085] Understandably, the second mixer 116 will convert the first mixer signal (the filtered difference frequency component, with a frequency of |f) into a single frequency. VCO -f LO2 |) and the K-fold frequency signal (frequency K×f) ref After mixing, the output second mixed signal simultaneously contains a sum frequency component (frequency of |f) VCO -f LO2 |+K× f ref ) and difference frequency component (frequency of ||f) VCO -f LO2 |-K× f ref The second intermediate frequency filter 119 is used to filter the second mixed signal before it enters the first phase detector 111, extracting the difference frequency component (frequency of ||f). VCO -f LO2 |-K× fref |) serves as a useful second mixing signal, while suppressing sum-frequency components and other spurious signals.

[0086] Furthermore, in some embodiments, the first local oscillator circuit 110 further includes a first local oscillator amplifier 120, used to amplify the power of the first oscillation signal to obtain the first local oscillator signal.

[0087] In some embodiments, the input of the first local oscillator amplifier 120 is connected to the first output of the first local oscillator coupler 114.

[0088] It is understandable that the first oscillation signal output from the first output terminal of the first local oscillator coupler 114 typically has a low power level (for example, the output power of the first oscillation signal is approximately 80% to 90% of the total output power of the oscillation signal). Therefore, in order to drive the receiver mixer to work normally, the first oscillation signal can be amplified by the first local oscillator amplifier 120 to output a first local oscillator signal LO1 with a higher power level, so as to better meet the local oscillator drive requirements of the receiver's first-stage mixer.

[0089] Taking a superheterodyne receiver employing two-stage frequency conversion as an example, at f LO2 =N×f ref In this case, the first local oscillator frequency obtained above in the present application can be further expressed as f LO1 = (K+1+N)×f ref The output frequency of the second-stage frequency converter (down-conversion) is f. IF2 = f LO1 – f RF – f LO2 The system phase noise output from the receiver's second-stage frequency conversion node obtained by the scheme in this application is PN. sys2 =PN ref ×(K+1+N - N) 2 + PN' PLL1 + PN PA1 + (PN PLL2 + PN PA2 ) - (PN PLL2 +PN PA2 ) = PN ref ×(K+1) 2 + PN' PLL1 + PN PA1 Among them, PN ref ×(K+1) 2 To generate phase noise for the reference signal after coherent cancellation, PN' PLL1 For the phase-locked loop integrated phase noise of the first local oscillator circuit 110, PN PA1 This is to introduce additional phase noise for the first local oscillator amplifier 120.

[0090] As can be seen from the above analysis, the scheme of this application achieves complete cancellation of the phase noise of the second local oscillator signal at the receiver's second-stage mixer node. Meanwhile, in existing local oscillator signal generation schemes based on dual independent phase-locked loop architectures using the same source reference signal, a frequency divider is installed within the phase-locked loop of the first local oscillator, which introduces additional digital switching noise, flicker noise, and phase jitter, thus causing the phase-locked loop of the first local oscillator to integrate phase noise PN. PLL1 The overall noise level is relatively high; however, this application uses a frequency multiplier and mixer instead of a frequency divider in the first local oscillator, completely avoiding the phase noise introduced by the frequency divider. Therefore, the phase-locked loop in the first local oscillator of this application integrates phase noise PN'. PLL1 Significantly lower PN than traditional methods PLL1 .

[0091] Furthermore, in existing local oscillator signal generation schemes based on dual independent phase-locked loop architectures with the same source reference signal, the first local oscillator frequency is f. LO1 = M×f ref In this application, f LO1 = (K+1+N)×f ref When the two are equal (i.e., when generating the same first local oscillator frequency), we have M×f ref = (K+1+N)×f ref Therefore, K+1 = MN. Thus, the reference signal derived phase noise in the system phase noise of the receiver's second-stage frequency conversion node obtained by the two schemes is equal, i.e., PN. ref ×(K+1) 2 =PN ref ×(M - N) 2 In other words, compared to existing solutions, the proposed solution can completely eliminate the PN of the second local oscillator signal in existing solutions while generating the same reference signal derived phase noise. PLL2 and PN PA2 Two types of incoherent phase noise, plus additional incoherent phase noise introduced by the frequency divider used in the local oscillator phase-locked loop.

[0092] In some embodiments, the local oscillator signal generation circuit 100 further includes: a first power divider 121, used to receive the signal output from the reference signal source and divide it into three paths, which are respectively used as reference signals provided to the first phase detector 111, reference signals provided to the K frequency multiplier 117 and reference signals provided to the second local oscillator circuit 210.

[0093] Please refer to Figure 5Some embodiments provide a structural example of a local oscillator signal generation circuit 100. In this circuit, a first power divider 121 coherently distributes the highly stable signal output from an external reference signal source to a first phase detector 111, a K-frequency multiplier 117, and a second phase detector 212. This coherence is a crucial foundation for achieving subsequent phase noise cancellation of the second local oscillator signal—only by ensuring that the first local oscillator circuit 110 and the second local oscillator circuit 210 share the same, phase-consistent reference signal source can the phase noise of the second local oscillator signal "embedded" in the first local oscillator signal be effectively coherently canceled with the phase noise of the second local oscillator signal output from the second local oscillator circuit 210 to the receiver's secondary mixing node.

[0094] Please refer to Figure 6 Some embodiments provide a superheterodyne receiver 300, including a first-stage mixer 310 and a second-stage mixer 320, and also includes the local oscillator signal generation circuit 100 described in any of the above embodiments of this application, wherein:

[0095] The local oscillator signal generation circuit 100 includes a first local oscillator circuit 110 and a second local oscillator circuit 210;

[0096] The first local oscillator circuit 110 is used to provide the first local oscillator signal required by the first-stage mixer unit 310;

[0097] The second local oscillator circuit 210 is used to provide the second local oscillator signal required by the secondary mixer unit 320.

[0098] In some embodiments, the output signal frequency f of the secondary mixer unit 320 is... IF2 The frequency f of the first local oscillator signal LO1 The frequency f of the second local oscillator signal LO2 and the frequency f of the radio frequency received signal RF Satisfy: f IF2 = f LO1 -f RF -f LO2 .

[0099] By employing the local oscillator signal generation circuit 100 of any of the above embodiments of this application in the superheterodyne receiver 300, since the first local oscillator circuit 110 accurately maps and embeds the phase noise of the second local oscillator signal LO2 into the first local oscillator signal LO1 through the dual mixing feedback structure, in the second mixing unit 320 of the superheterodyne receiver 300, when the first intermediate frequency signal (carrying the LO2 phase noise information embedded in LO1) output by the first mixing unit 310 is mixed with the second local oscillator signal LO2 again, the LO2 phase noise components in the two signals can cancel each other out through the subtraction operation of the receiver's second mixing because they have the same source and are coherent. Specifically, when the first-stage mixer unit 310 mixes LO1 with the RF received signal, the phase noise of LO2 is "copied" into the first intermediate frequency signal IF1 output by the first-stage mixer unit 310; the second-stage mixer unit 320 then subtracts this "copied" LO2 phase noise from the LO2 phase noise output by the second local oscillator circuit 210 to the second-stage mixer unit 320, thereby eliminating the LO2 phase noise and significantly reducing the total phase noise of the second intermediate frequency signal IF2 output by the second-stage mixer unit 320.

[0100] Furthermore, since no frequency divider is used in the feedback path of the first local oscillator circuit 110, the power supply noise, switching noise and flicker noise introduced by the frequency divider as an active digital device are avoided, which greatly reduces the phase noise floor of the first local oscillator signal, thereby improving the sensitivity and dynamic range of the entire receiver.

[0101] This document describes various exemplary embodiments with reference to them. However, those skilled in the art will recognize that changes and modifications can be made to the exemplary embodiments without departing from the scope of this document. For example, various operational steps and components for performing operational steps can be implemented in different ways depending on the specific application or considering any number of cost functions associated with the operation of the system (e.g., one or more steps can be deleted, modified, or combined with other steps).

[0102] While the principles herein have been illustrated in various embodiments, numerous modifications to the structures, arrangements, proportions, elements, materials, and components, particularly suited to specific environments and operational requirements, may be used without departing from the principles and scope of this disclosure. These modifications and other alterations or alterations will be included within the scope of this document. Those skilled in the art will recognize that many changes can be made to the details of the above embodiments without departing from the fundamental principles of the invention.

Claims

1. A local oscillator signal generation circuit, characterized in that, It includes a first local oscillator circuit and a second local oscillator circuit. The first local oscillator circuit is used to generate a first local oscillator signal based on a reference signal, and the second local oscillator circuit is used to generate a second local oscillator signal based on the reference signal; wherein: The first local oscillator circuit includes a first phase detector, a first loop filter, a first voltage-controlled oscillator, a first local oscillator coupler, a first mixer, a second mixer, and a K-multiplier. The K-frequency multiplier is used to multiply the reference signal by K to obtain a K-frequency signal; The first phase detector is used to generate an error signal based on the reference signal and the signal output by the second mixer; The first loop filter is used to generate a tuned voltage signal based on the error signal; The first voltage-controlled oscillator is used to generate an oscillation signal based on the tuning voltage signal; The first local oscillator coupler is used to generate and output a first oscillator signal and a second oscillator signal based on the oscillator signal, wherein the first oscillator signal is used to generate the first local oscillator signal; The first mixer is used to generate a first mixed signal based on the second oscillation signal and the second local oscillator signal; The second mixer is used to generate a second mixed signal based on the first mixed signal and the K-fold frequency signal and output it to the first phase detector.

2. The local oscillator signal generation circuit as described in claim 1, characterized in that, The frequency f of the first local oscillator signal LO1 The frequency f of the reference signal ref and the frequency f of the second local oscillator signal LO2 Satisfy: f LO1 = (K+1) × f ref +f LO2 .

3. The local oscillator signal generation circuit as described in claim 1, characterized in that, The first local oscillator circuit further includes: A first intermediate frequency filter is used to filter the first mixing signal before the second mixer generates the second mixing signal based on the first mixing signal and the K-fold frequency signal, so that the second mixer generates the second mixing signal based on the K-fold frequency signal and the filtered first mixing signal.

4. The local oscillator signal generation circuit as described in claim 1, characterized in that, The first local oscillator circuit further includes: The second intermediate frequency filter is used to filter the second mixing signal before the second mixer outputs the second mixing signal to the first phase detector, so as to output the filtered second mixing signal to the first phase detector.

5. The local oscillator signal generation circuit as described in claim 1, characterized in that, The first local oscillator circuit further includes: The first local oscillator amplifier is used to amplify the power of the first oscillation signal to obtain the first local oscillator signal.

6. The local oscillator signal generation circuit as described in claim 1, characterized in that, Also includes: The first power divider is used to receive the signal output from the reference signal source and split it into three paths, which are respectively used as reference signals for the first phase detector, reference signals for the K frequency multiplier, and reference signals for the second local oscillator circuit.

7. The local oscillator signal generation circuit as described in claim 1, characterized in that, The second local oscillator circuit uses a phase-locked loop based on a frequency divider for phase locking and frequency multiplication to generate the second local oscillator signal.

8. The local oscillator signal generation circuit as described in claim 1, characterized in that, The second local oscillator circuit includes: The second power divider is used to split the signal output from the second local oscillator circuit into two paths: one path serves as the second local oscillator signal output from the second local oscillator circuit, and the other path serves as the second local oscillator signal provided to the first mixer.

9. The local oscillator signal generation circuit as described in claim 8, characterized in that, The second local oscillator circuit also includes: a second phase detector, a second loop filter, a second voltage-controlled oscillator, a second local oscillator coupler, and a frequency divider.

10. A superheterodyne receiver, comprising a first-stage mixer unit and a second-stage mixer unit, characterized in that, It also includes the local oscillator signal generation circuit as described in any one of claims 1-9, wherein: The local oscillator signal generation circuit includes a first local oscillator circuit and a second local oscillator circuit; The first local oscillator circuit is used to provide the first local oscillator signal required by the first-stage mixer unit; The second local oscillator circuit is used to provide the second local oscillator signal required by the secondary mixer unit.

11. The superheterodyne receiver as described in claim 10, characterized in that, The output signal frequency f of the secondary mixer unit IF2 The frequency f of the first local oscillator signal LO1 The frequency f of the second local oscillator signal LO2 and the frequency f of the radio frequency received signal RF Satisfy: f IF2 = f LO1 -f RF -f LO2 .

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