A terahertz monolithic integrated subharmonic mixer based on a single-ended structure

Abstract

This invention provides a terahertz monolithically integrated subharmonic mixer based on a single-ended structure, relating to the field of terahertz mixer technology. The mixer includes a substrate on which a mixing circuit is formed. The local oscillator input port is connected to one end of a local oscillator matching filter structure and one end of a bias circuit via the output of a DC blocking capacitor. The other end of the local oscillator matching filter structure is connected to the gate of the mixer element, and the other end of the bias circuit is connected to the Vg power-on terminal. The radio frequency (RF) port is connected to an RF matching structure and an intermediate frequency (IF) filter structure via an RF filter structure. The other end of the RF matching structure is connected to the drain of the mixer element, and the other end of the IF filter structure is connected to the IF port. The mixer element is a common-source FET / HEMT die. This solution utilizes the square-law characteristics of the mixer element to realize a terahertz monolithically integrated subharmonic mixer based on a single-ended structure, exhibiting performance indicators such as low conversion loss, small size, and high port isolation over a wide bandwidth.

Description

Technical Field

[0001] This invention belongs to the field of terahertz mixer technology, and particularly relates to a terahertz monolithic integrated subharmonic mixer based on a single-ended structure. Background Technology

[0002] The high carrier frequency, high penetration, and large bandwidth of terahertz frequencies make them promising for applications in high-speed wireless communication, terahertz radar, and detection. As a key component, the performance of a terahertz system is significantly influenced by the quality of its technical specifications, such as operating bandwidth, conversion loss, and noise figure.

[0003] Terahertz-band monolithically integrated subharmonic mixers are mainly divided into two categories: balanced subharmonic mixers based on FET / HEMT and subharmonic mixers based on anti-parallel diode pair (APDP) structures. FET / HEMT-based balanced subharmonic mixers typically require two mixing units. The local oscillator signals supplied to these two units often employ stub lines to achieve 90° or 180° phase shifts, making it difficult to achieve broadband characteristics. This results in a larger chip size and double the required local oscillator drive power. APDP-based subharmonic mixers require fabrication processes compatible with Schottky barrier diode technology, imposing more limitations on the manufacturing process and consequently increasing manufacturing costs.

[0004] Cutoff frequency f T It is generally considered a metric for measuring the upper limit of the operating frequency of FET / HEMT, and is typically achieved by shortening the gate length to reduce the channel carrier transit time and increasing the cutoff frequency f. T Limited by current process technology and the short-channel effect, the gate length cannot be shortened indefinitely, thus limiting the cutoff frequency f of compound semiconductor FETs / HEMTs. T Terahertz mixers, as indispensable components in the transceiver front-end for frequency conversion, face the challenge of achieving frequencies higher than the cutoff frequency f of existing compound semiconductor FET / HEMT processes. T The G-band frequency band, with its considerable operating bandwidth, conversion loss, and noise figure, is a promising area for exploration. For example, Sten E. Gunnarsson et al. from Chalmers University of Technology in Sweden designed a 220GHz (G-band) monolithic integrated single-ended resistive fundamental mixer using 0.1µm GaAs mHEMT technology. Based on this technology, the 2x20µm mHEMT cutoff frequency f... TThe frequency is only 170GHz, lower than the mixer's operating frequency. This mixer has a minimum conversion loss of 8.7dB and exhibits good flatness in the 200-220GHz band. However, due to the insufficient output power of the local oscillator, it is difficult to further improve the mixer's conversion loss.

[0005] Therefore, considering the cutoff frequency f of FET / HEMT in the terahertz band compound semiconductor process... T The existing technology needs improvement due to challenges such as the difficulty of increasing performance and the lack of high-performance local oscillators in the terahertz high-frequency band. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a terahertz monolithic integrated subharmonic mixer based on a single-ended structure, which addresses the shortcomings of the prior art.

[0007] The technical solution of the present invention is as follows: A terahertz monolithic integrated subharmonic mixer based on a single-ended structure, characterized in that: it includes a substrate on which a mixing circuit is formed. The mixing circuit includes a local oscillator input port, a DC blocking capacitor, a bias circuit, a local oscillator matching filter structure, a mixing circuit, an RF matching structure, an RF filter structure, an RF port, an IF filter structure, and an IF port; the local oscillator input port is connected to one end of the local oscillator matching filter structure and one end of the bias circuit via the output terminal of the DC blocking capacitor; the other end of the local oscillator matching filter structure is connected to the gate of the mixing element; the other end of the bias circuit is connected to the Vg power-on terminal; the RF port is connected to the RF matching structure and the IF filter structure via the RF filter structure; the other end of the RF matching structure is connected to the drain of the mixing element; and the other end of the IF filter structure is connected to the IF port.

[0008] The mixer element is a common-source FET / HEMT die. When the RF signal is the input signal, it is mixed with the second harmonic of the local oscillator signal. The intermediate frequency (IF) signal generated by the mixing is filtered by the IF filter structure and then output. When the IF signal is the input signal, it is mixed with the second harmonic of the local oscillator signal. The RF signal generated by the mixing is matched and filtered by the RF matching structure and the RF filter structure before being output.

[0009] The mixer circuit described above is a microstrip line design. The local oscillator port is connected to one end of the local oscillator matching filter structure and one end of the bias circuit via the output of a DC blocking parallel plate capacitor. The bias circuit is a structure consisting of a series high-impedance resistor connected in parallel with a capacitor to ground. The aforementioned DC blocking capacitor and parallel capacitor are constructed using compound semiconductor technology, with two metal layers forming the upper and lower electrode plates of the capacitor. The high-impedance resistor is manufactured using thin-film resistor technology within the compound semiconductor process.

[0010] The RF filtering structure of the mixer described above is a high-pass filter, designed using a parallel coupled-line filter.

[0011] The intermediate frequency (IF) filter structure of the mixer described above is a two-stage low-pass filter. The first-stage filter uses a series microstrip line connected in parallel with an open-circuit stub, where the equivalent electrical length of the series microstrip line and the parallel open-circuit stub is one-quarter of the RF wavelength. The second-stage filter uses a series microstrip line connected in parallel with a capacitor to ground.

[0012] The frequency of the RF signal of the mixer mentioned above is twice the frequency of the local oscillator signal and the frequency of the intermediate frequency signal.

[0013] The above scheme uses a common-source FET / HEMT die as the mixer element. When the RF signal is the input signal, it is input through the drain of the FET / HEMT and, under gate bias voltage, is mixed with the second harmonic of the local oscillator signal pumped through the gate. The resulting intermediate frequency (IF) signal is filtered by an IF filter structure before being output. When the IF signal is the input signal, it is input through the drain of the FET / HEMT and, under gate bias voltage, is mixed with the second harmonic of the local oscillator signal pumped through the gate. The resulting RF signal is matched and filtered by an RF matching structure and an RF filter structure before being output. The frequency interval between the RF signal and the local oscillator signal is sufficiently large, and the isolation between the local oscillator and the RF port can be effectively improved through an RF high-pass filter. This structure utilizes the square-law characteristic of the mixer element to achieve second harmonic mixing of the local oscillator signal, which not only solves the problem of the lack of high-performance local oscillator sources in the terahertz high-frequency band, but also effectively utilizes the cutoff frequency f of the FET / HEMT. T This is a low-cost compound semiconductor process operating below the RF operating frequency and above the local oscillator operating frequency. Because the common-source FET / HEMT transistor exhibits near-pure resistive characteristics at its drain port over a wide bandwidth when the drain is unbiased, RF and IF signals connected to the FET / HEMT drain have a flat response over a wide bandwidth. Compared to traditional FET / HEMT-based balanced subharmonic mixers, this circuit has a simpler structure, shorter RF and local oscillator signal transmission paths, and achieves low-loss transmission.

[0014] Therefore, this circuit structure not only effectively addresses the cutoff frequency f of FET / HEMT in the terahertz band compound semiconductor process, but also... T This invention addresses challenges such as low conversion loss and the lack of high-performance local oscillators in the terahertz high-frequency band. It also effectively improves the operating bandwidth of the monolithically integrated terahertz subharmonic mixer, reduces the mixer's conversion loss, improves the isolation between the local oscillator and the RF port, and reduces the chip size. The terahertz monolithically integrated subharmonic mixer of this invention exhibits performance indicators such as low conversion loss, low manufacturing cost, and high port isolation over a wide bandwidth. Attached Figure Description

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0016] Figure 1 This is a schematic diagram of the subharmonic mixer described in an embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram of the structure of a 220GHz subharmonic mixer according to an embodiment of the present invention;

[0018] Figure 3 yes Figure 2 The simulation results of the frequency conversion loss of the subharmonic mixer are shown in the figure.

[0019] Figure 4 yes Figure 2 The simulation results of the local oscillator-to-RF port isolation of the subharmonic mixer are shown in the figure.

[0020] Figure 5 yes Figure 2 The figure shows the simulation results of the local oscillator-to-IF port isolation of the subharmonic mixer.

[0021] Figure 6 yes Figure 2 The figure shows the simulation results of the RF-to-IF port isolation of the subharmonic mixer. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] First, the frequency range in which this invention is applied will be explained. The most suitable application frequency band for this invention is the low end of the terahertz wave frequency range. At the low end of the terahertz frequency range, the cutoff frequency f of the compound semiconductor process FET / HEMT is limited. T The development of terahertz monolithic integrated mixers has encountered a bottleneck due to the high-performance local oscillator required for fundamental frequency mixers. The terahertz monolithic integrated subharmonic mixer based on a single-ended structure designed in this invention precisely solves the aforementioned problem.

[0024] like Figure 1As shown, this embodiment of the invention discloses a terahertz monolithic integrated subharmonic mixer based on a single-ended structure, including a substrate 12 on which a mixer circuit is formed. The mixer circuit is a microstrip line design. The local oscillator input port 1 is connected to one end of the local oscillator matching filter structure 5 and one end of the bias circuit 3 via the output terminal of a DC blocking capacitor 2. The bias circuit 3 is a structure with a series high-impedance resistor and a parallel capacitor to ground. The other end of the local oscillator matching filter structure 5 is connected to the gate of the mixer element 6, and the other end of the bias circuit 3 is connected to the Vg power-on terminal 4. The power requirement of the local oscillator signal is reduced by adjusting the gate bias voltage. The radio frequency port 11 is connected to the radio frequency matching structure 7 and the intermediate frequency filter structure 9 via the radio frequency filter structure 10. The radio frequency filter structure (10) is a high-pass filter with a parallel coupled-line filter design. This filter also has the function of DC isolation, without the need for additional DC blocking plate capacitors. The other end of the radio frequency matching structure 7 is connected to the drain of the mixer element 6, and the other end of the intermediate frequency filter structure 9 is connected to the intermediate frequency port 8. The intermediate frequency (IF) filter structure 9 is a two-stage low-pass filter design. The first-stage filter uses a series microstrip line connected in parallel with an open-circuit stub. The equivalent electrical length of the series microstrip line and the parallel open-circuit stub is one-quarter of the RF wavelength, mainly used to suppress RF signal leakage. The second-stage filter uses a series microstrip line connected in parallel with a capacitor to ground to improve the isolation between the local oscillator and the IF port 8. The mixer circuit uses a common-source FET / HEMT die. When the RF signal is the input signal, it is mixed with the second harmonic of the local oscillator signal. The resulting IF signal is filtered by the IF filter structure 9 before being output. When the IF signal is the input signal, it is mixed with the second harmonic of the local oscillator signal. The resulting RF signal is matched and filtered by the RF matching structure 7 and the RF filter structure 10 before being output. Compared to the lower transmission loss of coplanar waveguides at high frequencies, microstrip lines not only simplify the design layout but also effectively reduce the size of complex multifunctional chips. Therefore, this invention uses microstrip lines as the transmission lines for the mixer circuit, which is beneficial for further reducing chip size and manufacturing costs.

[0025] like Figure 2 The diagram shows a schematic of a single-ended terahertz monolithic integrated subharmonic mixer. Figure 3 The simulation results of the frequency conversion loss of the above mixer are based on the following operating conditions: radio frequency range of 210GHz to 230GHz, local oscillator of 105GHz, and intermediate frequency range of DC to 20GHz. Figure 4 The simulation results for the isolation between the local oscillator port and the radio frequency port are shown. The operating conditions are: radio frequency range of 210GHz to 230GHz, local oscillator 105GHz, and intermediate frequency range of DC to 20GHz. Figure 5The simulation results for the isolation between the local oscillator port and the intermediate frequency port are shown. The operating conditions are: RF frequency range of 210GHz to 230GHz, local oscillator 105GHz, and intermediate frequency range of DC to 20GHz. Figure 6 The simulation results for the isolation between the RF port and the IF port are shown. The operating conditions are: RF frequency range of 210GHz to 230GHz, local oscillator of 105GHz, and IF frequency range of DC to 20GHz.

[0026] The terahertz monolithic integrated subharmonic mixer based on a single-ended structure proposed in this invention has the following characteristics and innovations:

[0027] (1) Low cost: The above mixer not only effectively reduces the cutoff frequency f of FET / HEMT in compound semiconductor processes, but also reduces the cost of existing mixers. T This not only meets the requirements of reducing manufacturing costs but also eliminates the need for expensive, high-performance local oscillators;

[0028] (2) Operating bandwidth: The mixer described above uses a common-source FET / HEMT transistor. When its drain is unbiased, the drain port exhibits almost purely resistive characteristics over a wide bandwidth, thus enabling the RF and IF signals connected to the drain of the FET / HEMT transistor to have a flat response over a wide operating bandwidth. Compared to traditional balanced subharmonic mixers based on FET / HEMT, it does not require stub lines to achieve 90° or 180° phase shift and also achieves broadband characteristics well;

[0029] (3) Low conversion loss: Compared with traditional balanced subharmonic mixers based on FET / HEMT, this circuit has a simple structure, short transmission paths for RF and local oscillator signals, and achieves low-loss transmission.

[0030] (4) Small size: The above mixer adopts a microstrip line design, which simplifies the layout; it utilizes the square law characteristics of the mixing element to realize the second harmonic mixing of the local oscillator signal, thus reducing the chip size;

[0031] (5) High isolation: The frequency interval between the RF signal and the local oscillator signal is large enough, and the isolation between the local oscillator and the RF port is effectively improved by the RF high-pass filter; the intermediate frequency filter structure adopts a two-stage low-pass filter design, which effectively suppresses the leakage of the RF signal and the local oscillator signal to the intermediate frequency port.

[0032] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A single-ended structure based terahertz monolithic integrated subharmonic mixer, characterized by: The mixer circuit comprises a substrate, and a mixer circuit is formed on the substrate, the mixer circuit comprises a local oscillator input port, a direct current blocking capacitor, a bias circuit, a local oscillator matching filter structure, a mixer element, a radio frequency matching structure, a radio frequency filter structure, a radio frequency port, an intermediate frequency filter structure, and an intermediate frequency port. The local oscillator input port is connected to one end of the local oscillator matching filter structure and one end of the bias circuit through the output end of the direct current blocking capacitor. The radio frequency port is connected to the radio frequency matching structure and the intermediate frequency filter structure through the radio frequency filter structure. The mixer element is a common source structure FET / HEMT die, when the radio frequency signal is an input signal, the second harmonic of the local oscillator signal is mixed, and the intermediate frequency signal generated by the mixing is filtered by the intermediate frequency filter structure and then output. When the intermediate frequency signal is an input signal, the second harmonic of the local oscillator signal is mixed, and the radio frequency signal generated by the mixing is matched and filtered by the radio frequency matching structure and the radio frequency filter structure and then output. The mixer circuit is designed as a microstrip line, the local oscillator input port is connected to one end of the local oscillator matching filter structure and one end of the bias circuit through the output end of a direct current blocking plate capacitor, and the bias circuit is a structure of a high-impedance resistor connected in series and a capacitor connected in parallel to the ground. The direct current blocking plate capacitor and the parallel capacitor are plate capacitors of a metal-insulator-metal structure in a compound semiconductor process, and the high-impedance resistor is a thin film resistor in a compound semiconductor process.

2. A single-ended structure based terahertz monolithic integrated subharmonic mixer as claimed in claim 1, characterized by: The radio frequency filter structure is a high-pass filter designed as a parallel coupled line filter.

3. The single-ended structure based terahertz monolithic integrated subharmonic mixer as claimed in claim 1, wherein: The intermediate frequency filter structure is a two-stage low-pass filter, the first-stage filter is designed as a structure of a microstrip line connected in series and an open-circuit stub connected in parallel, the equivalent electrical length of the microstrip line and the open-circuit stub is one fourth of the radio frequency wavelength, and the second-stage filter is designed as a structure of a microstrip line connected in series and a capacitor connected in parallel to the ground.

4. The single-ended structure based terahertz monolithic integrated subharmonic mixer as claimed in claim 1, wherein: The frequency of the radio frequency signal is the sum of twice the frequency of the local oscillator signal and the frequency of the intermediate frequency signal.

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