Direct current suppression circuit structure, direct current suppression method and terahertz heterodyne detection system

Abstract

This invention discloses a DC suppression circuit structure, a DC suppression method, and a terahertz heterodyne detection system. The DC suppression circuit structure includes a first nonlinear detection module, a second nonlinear detection module, a phase adjustment module, and a signal synthesis module. The phase adjustment module adjusts the phase of the mixing signal generated by the second nonlinear detection module. The signal synthesis module superimposes the phase-adjusted mixing signal with the mixing signal generated by the first nonlinear detection module. During the synthesis process, the self-mixing DC component is at least partially canceled out, and the intermediate frequency AC component is at least partially superimposed. This invention weakens or cancels the self-mixing DC component during the synthesis process, while allowing the intermediate frequency AC component to be superimposed and output, thereby effectively suppressing the self-mixing DC component in the output signal and improving the stability of the intermediate frequency signal.

Description

Technical Field

[0001] This invention relates in particular to a DC suppression circuit structure, a DC suppression method, and a terahertz heterodyne detection system, belonging to the field of terahertz detection technology. Background Technology

[0002] Terahertz heterodyne detection technology, due to its high sensitivity and spectral resolution, has broad application prospects in terahertz communication, terahertz imaging, and spectral analysis. In heterodyne detection systems, nonlinear devices are typically used as mixers to achieve frequency mixing of the local oscillator signal and the measured terahertz signal.

[0003] High electron mobility transistor (HMT) terahertz detectors are widely used in terahertz heterodyne detection systems due to their high carrier mobility and fast response speed. In heterodyne detection mode, when the local oscillator signal and the measured terahertz signal simultaneously act on the HMT terahertz detector, a mixing current is generated between its source and drain. This mixing current typically contains both a DC component generated by the self-mixing effect and an intermediate frequency (IF) AC component. The IF AC component characterizes the measured signal information, while the DC component does not participate in information carrying and introduces additional noise background into the downstream signal link, potentially causing the operating point of the downstream amplifier circuit to drift, thereby reducing the system's signal-to-noise ratio and overall stability.

[0004] To reduce the adverse effects of DC components on system performance, existing technologies typically employ post-stage filtering or DC blocking circuits to process the output signal. However, these methods often rely on specific cutoff frequency designs, which can easily affect the integrity of the intermediate frequency signal and make it difficult to eliminate the adverse effects of DC components at the system structure level. Therefore, it is still necessary to propose a terahertz heterodyne detection circuit structure that is simple in structure, highly versatile, and can effectively suppress DC components during the current synthesis stage. Summary of the Invention

[0005] The purpose of this invention is to address the problem that existing terahertz detectors, in heterodyne detection mode, simultaneously generate self-mixing DC components and intermediate frequency AC components at the output due to nonlinear mixing effects. The self-mixing DC component does not participate in information carrying and introduces noise background, affecting the stability of back-end circuits and reducing the system's signal-to-noise ratio. This invention provides a DC suppression circuit structure, a DC suppression method, and a terahertz heterodyne detection system. By effectively canceling the self-mixing DC component during the current synthesis stage, only the useful intermediate frequency AC signal component is retained, thereby reducing the DC component and noise background at the output port, improving the signal-to-noise ratio and overall operational stability of the heterodyne detection system, and overcoming the shortcomings of existing technologies.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: A first aspect of the present invention provides a DC suppression circuit structure for terahertz heterodyne detection, comprising: The first nonlinear detection module and the second nonlinear detection module generate a mixed signal containing a self-mixing DC component and an intermediate frequency AC component under terahertz signal excitation. The system includes a phase adjustment module and a signal synthesis module. The phase adjustment module is electrically connected to the second nonlinear detection module. The signal synthesis module is connected to both the first nonlinear detection module and the phase adjustment module. The phase adjustment module is used to adjust the phase of the mixing signal generated by the second nonlinear detection module. The signal synthesis module is used to superimpose and synthesize the phase-adjusted mixing signal with the mixing signal generated by the first nonlinear detection module. During the synthesis process, the self-mixed DC components at least partially cancel each other out, and the intermediate frequency AC components at least partially superimpose.

[0007] Furthermore, the first nonlinear detection module and the second nonlinear detection module have the same structural and electrical parameters. When the same bias voltage is applied, they operate in the same working state, and the amplitudes of the self-mixing DC components generated by the first nonlinear detection module and the second nonlinear detection module are the same.

[0008] Furthermore, the first nonlinear detection module and the second nonlinear detection module operate in a symmetrical manner.

[0009] Furthermore, both the first nonlinear detection module and the second nonlinear detection module are high electron mobility transistor terahertz detectors. The source of the first nonlinear detection module and the drain of the second nonlinear detection module are grounded. The first nonlinear detection module and the second nonlinear detection module are in a symmetrical working state in terms of electrical structure. The source of the second nonlinear detection module is connected to the phase adjustment module.

[0010] For example, the high electron mobility transistor terahertz detector may be a silicon-based device, a gallium arsenide-based device, a gallium nitride-based device, an indium phosphide-based device, or a graphene-based device, etc.

[0011] Furthermore, the first nonlinear detection module and the second nonlinear detection module simultaneously receive the local oscillator terahertz signal and the measured terahertz signal, and the frequency of the intermediate frequency AC component corresponds to the frequency difference between the local oscillator terahertz signal and the measured terahertz signal.

[0012] Furthermore, the phase adjustment module adjusts the phase angle of the mixing signal by more than 0° and not more than 180°.

[0013] Furthermore, the phase adjustment module adjusts the phase of the mixing signal by 180°, and the self-mixing DC components in the two mixing signals have opposite polarities, while the phase relationship of the intermediate frequency AC components is the same.

[0014] Furthermore, the phase adjustment module includes a passive phase shifting network or an active phase reversing circuit, wherein the passive phase shifting network includes a transmission line phase shifting structure, and the active phase reversing circuit includes a phase control circuit based on an amplifier or an inverter.

[0015] Furthermore, the signal synthesis module includes an adder circuit or other equivalent circuit structure.

[0016] A second aspect of this invention provides a terahertz heterodyne detection system, comprising: The DC suppression circuit structure described above; and The signal coupling structure is electrically connected to or integrated with the first nonlinear detection module and the second nonlinear detection module, and is used to couple external terahertz signals to the active regions of the first nonlinear detection module and the second nonlinear detection module.

[0017] Furthermore, the signal coupling structure simultaneously couples the local oscillator terahertz signal and the measured terahertz signal to the first nonlinear detection module and the second nonlinear detection module.

[0018] Furthermore, the signal coupling structure can be an integrated planar antenna, a waveguide coupling structure, a near-field coupling structure, or other structural forms suitable for terahertz signal coupling.

[0019] A third aspect of this invention provides a DC suppression method for terahertz heterodyne detection, comprising: The first nonlinear detection module and the second nonlinear detection module are used to receive external terahertz signals and independently generate a mixed signal containing a self-mixing DC component and an intermediate frequency AC component under its excitation. The phase of the mixing signal generated by the second nonlinear detection module is adjusted, and the phase-adjusted mixing signal is superimposed and synthesized with the mixing signal generated by the first nonlinear detection module. The self-mixing DC components of the two mixing signals are at least partially canceled out, and the intermediate frequency AC components are at least partially superimposed and output.

[0020] Furthermore, the phase adjustment angle of the mixed signal is greater than 0° and does not exceed 180°.

[0021] In a preferred embodiment, the first nonlinear detection module and the second nonlinear detection module are symmetrically positioned in terms of electrical structure. The first nonlinear detection module and the second nonlinear detection module have the same structural and electrical parameters and operate in the same state, so that the amplitudes of the self-mixing DC components generated by the first nonlinear detection module and the second nonlinear detection module are the same. In addition, the phase adjustment angle of the mixing signal is 180°. The polarities of the self-mixing DC components in the two mixing signals are opposite, and the phase relationship of the intermediate frequency AC components is the same. The self-mixing DC components of the two mixing signals cancel each other out during the synthesis process, and the intermediate frequency AC components are superimposed and output.

[0022] Furthermore, the DC suppression method for terahertz heterodyne detection is implemented based on the DC suppression circuit structure or the terahertz heterodyne detection system.

[0023] Compared with the prior art, the advantages of the present invention include: This invention achieves effective suppression of the self-mixing DC component in the output signal and improves the stability of the intermediate frequency signal by performing phase reversal on one of the two mixing signals and combining it with the other mixing signal.

[0024] This invention introduces two nonlinear detection modules with consistent structural parameters and operating states, and combines them with phase adjustment and current synthesis circuits to effectively suppress the self-mixing DC component during heterodyne terahertz detection. At the same time, it helps to suppress the noise background in the output signal, improves the signal-to-noise ratio and detection sensitivity of the heterodyne detection system, avoids the operating point drift caused by DC bias changes in the back-end signal processing circuit, and improves the stability and consistency of system operation.

[0025] This invention does not depend on a specific material system or a specific terahertz signal coupling method, and has good versatility and engineering application prospects. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a system block diagram of a DC suppression circuit structure for terahertz heterodyne detection provided in a typical embodiment of the present invention; Figure 2This is a schematic diagram of a DC suppression circuit structure for terahertz heterodyne detection provided in a typical embodiment of the present invention; Figure 3a This is a typical embodiment of the present invention, showing the relationship between the power-related quantities of the mixing current generated by the first HEMT terahertz detector and the second HEMT terahertz detector under the same excitation conditions and the change over time. Figure 3b This is a typical embodiment of the present invention, showing the change of the corresponding power-related quantity over time after introducing a 180° phase flip into the mixing current generated by the second HEMT terahertz detector. Figure 3c This is a typical embodiment of the present invention, showing the change of the power-related quantity of the output signal over time after the two mixing currents are synthesized. Detailed Implementation

[0027] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0028] To make the objectives, technical solutions, and beneficial effects of this invention clearer and more complete, the specific embodiments of this invention will be further described below with reference to the accompanying drawings. It should be understood that the following embodiments are only used to explain the technical concept of this invention and do not constitute a limitation on the scope of protection of this invention. Those skilled in the art can make various modifications or equivalent substitutions to the described embodiments without departing from the technical concept and scope of the claims, and all such modifications or substitutions should fall within the scope of protection of this invention.

[0029] In a more typical implementation scheme, please refer to Figure 1 A terahertz heterodyne detection system includes a signal coupling structure, a first HEMT terahertz detector (i.e., a first high electron mobility transistor terahertz detector, hereinafter the same) D1, a second HEMT terahertz detector (i.e., a second high electron mobility transistor terahertz detector, hereinafter the same) D2, a phase adjustment module, and a current synthesis module. The signal coupling structure is electrically connected to the first HEMT terahertz detector D1 and the second HEMT terahertz detector D2, respectively, and is used to couple external terahertz signals (including local oscillator terahertz signals and measured terahertz signals) to the active regions of the first HEMT terahertz detector D1 and the second HEMT terahertz detector D2. The phase adjustment module is electrically connected to the second HEMT terahertz detector. The signal synthesis module is connected to the first HEMT terahertz detector and the phase adjustment module respectively. The phase adjustment module and the signal synthesis module are configured to form a DC suppression unit / structure. The DC suppression unit / structure synthesizes the two mixing signals generated by the first HEMT terahertz detector D1 and the second HEMT terahertz detector D2 and outputs them. In addition, during the synthesis process, the self-mixing DC component of the two mixing signals is at least partially canceled out, and the intermediate frequency AC component is at least partially superimposed.

[0030] This invention performs phase flipping on one of the two mixing signals and combines it with the other mixing signal. This weakens or cancels the self-mixing DC component during the synthesis process, while the intermediate frequency AC component is superimposed on the output signal. This effectively suppresses the DC component in the output signal and improves the stability of the intermediate frequency signal.

[0031] Specifically, the terahertz heterodyne detection system preferably includes two signal coupling structures, which are electrically connected to the first HEMT terahertz detector D1 and the second HEMT terahertz detector D2, respectively.

[0032] Specifically, the first HEMT terahertz detector D1 and the second HEMT terahertz detector D2 are identical in structural and electrical parameters, both have the same bias voltage applied to their gates, and operate in the same working state.

[0033] During operation, the local oscillator terahertz signal and the measured terahertz signal are simultaneously coupled to the active regions of the first HEMT terahertz detector D1 and the second HEMT terahertz detector D2 through a signal coupling structure. Under the same excitation conditions, based on the nonlinear characteristics of the high electron mobility transistor (HEMT), mixing currents are generated between the source and drain of the first HEMT terahertz detector D1 and the second HEMT terahertz detector D2, respectively. The mixing currents include a self-mixing DC component and an intermediate frequency AC component. The self-mixing DC component originates from the self-mixing effect of the local oscillator terahertz signal and the measured terahertz signal in the high electron mobility transistor. The intermediate frequency AC component originates from the mixing effect of the local oscillator terahertz signal and the measured terahertz signal in the high electron mobility transistor, and its frequency corresponds to the frequency difference between the local oscillator terahertz signal and the measured terahertz signal.

[0034] Since the first HEMT terahertz detector D1 and the second HEMT terahertz detector D2 are consistent in structural parameters and operating conditions, the self-mixing DC components generated by the two under the same terahertz excitation conditions have consistent amplitude characteristics, thus providing a basis for subsequent cancellation of the self-mixing DC components through phase reversal and current synthesis.

[0035] Please see Figure 2 , Figure 2 This is a schematic diagram of a DC suppression circuit structure for terahertz heterodyne detection in one embodiment of the present invention. The first HEMT terahertz detector D1 and the second HEMT terahertz detector D2 are connected symmetrically, and the self-mixing DC component is canceled and the intermediate frequency AC component is synthesized and output through a phase adjustment module and a current synthesis module. Specifically, in terms of circuit connection, the source of the first HEMT terahertz detector D1 and the drain of the second HEMT terahertz detector D2 are grounded, and the two HEMT terahertz detectors form a symmetrical operating state in electrical structure. The source output current of the second HEMT terahertz detector D2 is introduced into the phase adjustment module, and the current signal undergoes a 180° phase flip. The output current of the second HEMT terahertz detector D2 (i.e., the mixing current) after phase flipping and the drain output current of the first HEMT terahertz detector D1 (i.e., the mixing current) are jointly input to the current synthesis module for synthesis. Since the self-mixing DC components in the two mixing currents are equal in amplitude and opposite in polarity, they cancel each other out during the current synthesis process; while the intermediate frequency AC components have the same phase relationship after phase reversal, thus achieving superposition output during the current synthesis process. Therefore, the self-mixing DC components can be effectively suppressed at the synthesis output end, and only the intermediate frequency AC signal components are retained.

[0036] Please see Figure 3a , Figure 3b , Figure 3c , Figure 3a This diagram illustrates the relationship between the power-related quantities of the mixing current generated by the first HEMT terahertz detector and the second HEMT terahertz detector under the same excitation conditions and the change over time. Figure 3b This diagram illustrates the relationship between the power-related quantities and time after a 180° phase reversal is introduced into the mixing current generated by the second HEMT terahertz detector. Figure 3c The diagram illustrates the change in power correlation quantity of the output signal over time after combining the two mixing currents. This demonstrates that the DC correlation components generated during the mixing process cancel each other out, while the intermediate frequency AC components are superimposed in the output. It shows that through phase reversal and current combining, this invention can effectively suppress the DC correlation component in the heterodyne mixing current, thereby reducing DC interference in the output signal, improving the system's ability to effectively extract intermediate frequency signals, and ultimately improving the signal-to-noise characteristics and operational stability of the terahertz heterodyne detection system.

[0037] In one alternative embodiment, the phase adjustment module may employ a phase shifter, which may be implemented through a passive phase shifting network (e.g., a transmission line phase shifting structure, etc.) or through an active phase inversion circuit (e.g., a phase control circuit based on an amplifier or inverter, etc.). The present invention does not specifically limit the implementation of the phase shifter.

[0038] In one optional embodiment, the current combining module is used to combine the output currents of the first detection branch (including a terahertz wave coupling structure and a first HEMT terahertz detector D1) and the second detection branch (including a terahertz wave coupling structure and a second HEMT terahertz detector D2). The current combining module can employ an adder circuit or other circuit structure capable of superimposing multiple currents or equivalent signals; its specific implementation / structure is not limited. The current combining module can be connected to the two detection branches using a common node connection method, such as a T-junction structure, a metal interconnect node, or an equivalent low-impedance bus structure.

[0039] In another alternative embodiment, the high electron mobility transistor terahertz detector can be implemented using different material systems and device structures, as long as it possesses nonlinear response characteristics in the terahertz frequency band and can generate a mixing current between the source and drain. For example, the high electron mobility transistor terahertz detector can be fabricated using semiconductor material systems such as silicon-based, gallium arsenide, gallium nitride, and indium phosphide, and this invention does not limit it to these methods.

[0040] Furthermore, the HEMT terahertz detector can be electrically connected to or integrated with a signal coupling structure, which is used to couple external terahertz signals to the active region of the HEMT terahertz detector. Typically, the signal coupling structure can be an integrated planar antenna, a waveguide coupling structure, a near-field coupling structure, or other structural forms suitable for introducing terahertz signals; this invention does not limit such applications.

[0041] With the above-described structural design, the technical solution provided by this invention is beneficial for reasonably controlling different components in the output signal while keeping the system structure relatively simple, thereby improving the signal-to-noise characteristics and overall performance of the terahertz receiving system.

[0042] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A DC suppression circuit structure for terahertz heterodyne detection, characterized in that, include: The first nonlinear detection module and the second nonlinear detection module generate a mixed signal containing a self-mixing DC component and an intermediate frequency AC component under terahertz signal excitation. The system includes a phase adjustment module and a signal synthesis module. The phase adjustment module is electrically connected to the second nonlinear detection module. The signal synthesis module is connected to both the first nonlinear detection module and the phase adjustment module. The phase adjustment module is used to adjust the phase of the mixing signal generated by the second nonlinear detection module. The signal synthesis module is used to superimpose and synthesize the phase-adjusted mixing signal with the mixing signal generated by the first nonlinear detection module. During the synthesis process, the self-mixed DC components at least partially cancel each other out, and the intermediate frequency AC components at least partially superimpose.

2. The DC suppression circuit structure for terahertz heterodyne detection according to claim 1, characterized in that: The first nonlinear detection module and the second nonlinear detection module have the same structural and electrical parameters. When the same bias voltage is applied, they operate in the same working state. The amplitudes of the self-mixing DC components generated by the first nonlinear detection module and the second nonlinear detection module are the same. Preferably, the first nonlinear detection module and the second nonlinear detection module operate in a symmetrical manner.

3. The DC suppression circuit structure for terahertz heterodyne detection according to claim 1 or 2, characterized in that: Both the first nonlinear detection module and the second nonlinear detection module are high electron mobility transistor terahertz detectors. The source of the first nonlinear detection module and the drain of the second nonlinear detection module are grounded. The first nonlinear detection module and the second nonlinear detection module are in a symmetrical working state in terms of electrical structure. The source of the second nonlinear detection module is connected to the phase adjustment module. Preferably, the first nonlinear detection module and the second nonlinear detection module simultaneously receive the local oscillator terahertz signal and the measured terahertz signal, and the frequency of the intermediate frequency AC component corresponds to the frequency difference between the local oscillator terahertz signal and the measured terahertz signal.

4. The DC suppression circuit structure for terahertz heterodyne detection according to claim 1 or 2, characterized in that: The phase adjustment module adjusts the phase of the mixing signal by an angle greater than 0° and not exceeding 180°. Preferably, the phase adjustment module adjusts the phase of the mixing signal by 180°, and the self-mixing DC components in the two mixing signals have opposite polarities, while the phase relationship of the intermediate frequency AC components is the same.

5. The DC suppression circuit structure for terahertz heterodyne detection according to claim 1, characterized in that: The phase adjustment module includes a passive phase shifting network or an active phase reversing circuit, wherein the passive phase shifting network includes a transmission line phase shifting structure, and the active phase reversing circuit includes a phase control circuit based on an amplifier or an inverter. And / or, the signal synthesis module includes an adder circuit.

6. A terahertz heterodyne detection system, characterized in that, include: The DC suppression circuit structure as described in any one of claims 1-5; as well as The signal coupling structure is electrically connected to or integrated with the first nonlinear detection module and the second nonlinear detection module, and is used to couple external terahertz signals to the active regions of the first nonlinear detection module and the second nonlinear detection module.

7. The terahertz heterodyne detection system according to claim 6, characterized in that: The signal coupling structure simultaneously couples the local oscillator terahertz signal and the measured terahertz signal to the first nonlinear detection module and the second nonlinear detection module. Preferably, the signal coupling structure is an integrated planar antenna, a waveguide coupling structure, or a near-field coupling structure.

8. A DC suppression method for terahertz heterodyne detection, characterized in that, include: The first nonlinear detection module and the second nonlinear detection module are used to receive external terahertz signals and independently generate a mixed signal containing a self-mixing DC component and an intermediate frequency AC component under its excitation. The phase of the mixing signal generated by the second nonlinear detection module is adjusted, and the phase-adjusted mixing signal is superimposed and synthesized with the mixing signal generated by the first nonlinear detection module. The self-mixing DC components of the two mixing signals are at least partially canceled out, and the intermediate frequency AC components are at least partially superimposed and output.

9. The DC suppression method for terahertz heterodyne detection according to claim 8, characterized in that: The phase adjustment angle of the mixed signal is greater than 0° and does not exceed 180°; Preferably, the first nonlinear detection module and the second nonlinear detection module are symmetrically positioned in terms of electrical structure. The structural and electrical parameters of the first nonlinear detection module and the second nonlinear detection module are the same, and they operate in the same working state. This ensures that the amplitudes of the self-mixing DC components generated by the first nonlinear detection module and the second nonlinear detection module are the same. Furthermore, the phase adjustment angle of the mixing signal is 180°. The polarities of the self-mixing DC components in the two mixing signals are opposite, and the phase relationship of the intermediate frequency AC components is the same. The self-mixing DC components of the two mixing signals cancel each other out during the synthesis process, and the intermediate frequency AC components are superimposed and output.

10. The DC suppression method for terahertz heterodyne detection according to claim 8 or 9, characterized in that: The DC suppression method for terahertz heterodyne detection is implemented based on the DC suppression circuit structure of any one of claims 1-5 or the terahertz heterodyne detection system of claim 5 or 6.

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