阅读说明：本技术 一种应用于汽车防撞雷达的e波段混频器 (E-band mixer applied to automobile anti-collision radar ) 是由 康凯 李朋林 吴韵秋 赵晨曦 刘辉华 余益明 于 2019-09-06 设计创作，主要内容包括：本发明属于无线通信技术领域,涉及汽车防撞雷达,具体为一种应用于汽车防撞雷达的混频器,包括：跨导级单元、变压器短截线耦合单元、开关级单元、负载级单元、缓冲级单元。本发明采用变压器短截线耦合的共源共栅的结构,变压器放置于开关级和跨导级之间,共源共栅配置的直流通路被变压器分隔开,为跨导级和开关级提供独立的偏置,抵消跨导级的三阶非线性跨导,提升线性度；同时,在E波段采用电磁耦合技术与开路短截线相结合,抵消跨导级和开关级的寄生电容以及结电容,解决随着频率升高混频器噪声恶化的问题,降低噪声,同时避免在混频器设计中引入这两个电感将会占据很大芯片面积节省芯片面积,减少产品成本。(The invention belongs to the technical field of wireless communication, relates to an automobile anti-collision radar, and particularly relates to a frequency mixer applied to the automobile anti-collision radar, which comprises: the transformer comprises a transconductance stage unit, a transformer stub coupling unit, a switch stage unit, a load stage unit and a buffer stage unit. The invention adopts a structure of a cascode coupled by a transformer stub, the transformer is arranged between a switch stage and a transconductance stage, and a direct current path configured by the cascode is separated by the transformer to provide independent bias for the transconductance stage and the switch stage, so as to offset three-order nonlinear transconductance of the transconductance stage and improve linearity; meanwhile, the electromagnetic coupling technology is combined with the open stub in the E wave band, parasitic capacitance and junction capacitance of the transconductance stage and the switch stage are offset, the problem of noise deterioration of the frequency mixer along with frequency rise is solved, noise is reduced, the two inductors are prevented from occupying a large chip area in the design of the frequency mixer, the chip area is saved, and the product cost is reduced.)

1. An E-band mixer applied to an automobile anti-collision radar, comprising: the transformer short-section line coupling circuit comprises a transconductance stage unit (1), a transformer short-section line coupling unit (2), a switching stage unit (3), a load stage unit (4) and a buffer stage unit (5); the method is characterized in that:

the transconductance stage unit (1) comprises an NMOS tube M₁NMOS transistor M₂Wherein, the NMOS tube M₁NM OS tube M₂Source electrodes are all grounded, and NMOS tube M₁A grid electrode is connected with a positive input end of a radio frequency signal, and an NMOS tube M₂The grid is connected with the negative input end of the radio frequency signal, and the NMOS tube M₁The drain electrode is connected with the preceding stage inductor L of the transformer₁Homonymous terminal and NMOS tube M₂The drain electrode is connected with the primary inductor L of the transformer₁A synonym terminal;

the transformer stub coupling unit (2) comprises a transformer T, two open-circuit stubs and a capacitor C₅And a capacitor C₆Wherein the transformer T is composed of a primary coil L₁And a secondary coil L₂Composition, primary coil L₁Is tapped at the center V_DDSecondary winding L₂Is grounded, and the secondary coil L₂Two ends of the short stub are respectively connected in series with an open-circuit stub, and the other ends of the two open-circuit stubs are respectively connected in series with a capacitor C₅Capacitor C₆To the ground;

the switch stage unit (3) comprises an NMOS tube M₃NMOS tube M₄NMOS transistor M₅And NMOS tube M₆Wherein, the NMOS tube M₄And NMOS transistor M₅Grid interconnection is connected with negative input end of local oscillator signal, and NMOS tube M₃And NMO S pipe M₆Grid interconnection is connected with positive input end of local oscillator signal and NMOS tube M₃And NMOS transistor M₄Transformer secondary inductance L of source electrode interconnection transformer coupling unit₂End of same name, NMOS tube M₅And NMOS transistor M₆Transformer secondary inductance L of source electrode interconnection transformer coupling unit₂Different name end, NMOS tube M₃And NMOS transistor M₅Is interconnected with the drain electrode of the NMOS tube M₄And NMO S pipe M₆The drain electrode of (a);

the load stage unit (4) comprises two identical inductors L₃、L₄(L₃＝L₄) And two identical capacitors C₃、C₄(C₃＝C₄) (ii) a Inductor L₃And a capacitor C₃Connected in parallel as a group, and one end of the power supply is connected with a power supply voltage V_DDThe other end is connected with an NMOS tube M₃NMOS transistor M₅The drain electrode of the first transistor is connected with and used as a positive output end of the intermediate frequency signal; inductor L₄And a capacitor C₄Connected in parallel to another group, one end of which is connected to the power supply voltage V_DDThe other end is connected with an NMOS tube M₄NMOS transistor M₆The drain electrode of the first transistor is connected with and used as a negative output end of the intermediate frequency signal;

buffer unit (5) include that two the same transimpedance amplifiers place respectively at intermediate frequency signal positive output and intermediate frequency signal negative output, the transimpedance amplifier comprises electric group, NMOS pipe, PMOS pipe and coupling capacitance, wherein, intermediate frequency signal output is connected to coupling capacitance one end, the electric group is connected to the other end, the resistance other end is as mixer intermediate frequency signal output, NMOS pipe source ground connection, grid and drain-source are parallelly connected in resistance both ends, the grid and the drain-source of PMOS pipe correspond respectively with NMOS pipe grid and drain-source and are connected, source-source connection power supply voltage V_DD。

2. The E-band mixer for automotive anti-collision radar according to claim 1, wherein all field effect transistors are replaced by bipolar transistors, specifically: the NPN type triode replaces an NMOS tube, and the PNP type triode replaces a PMOS tube.

Technical Field

The invention belongs to the technical field of wireless communication, relates to an automobile anti-collision radar, and particularly relates to an E-band mixer applied to the automobile anti-collision radar.

Background

In recent years, with the rapid development of wireless communication technology, various wireless transceivers are developing to a higher operating frequency band to pursue higher bandwidth, data rate and lower delay, and millimeter wave (millimeter wave) frequency has attracted much attention. New products and services have already emerged great market potential, for example, in the development of ultra-high-speed and ultra-high-frequency end WLAN systems, the 60GHz 802.11ad communication system and the LTE network technology are combined through the LWA network, in the future 5G era, the excellent user experience can be brought to users, the wireless optical fiber access can be realized in E bands (71-75 GHz, 81-85 GHz and 92-95 GHz), and the 77GHz collision-avoidance radar for advanced driver assistance can be realized. For these applications, the fabrication of millimeter wave devices based on CMOS processes has the attractiveness of high integration and low cost; however, the poor linearity of the device at high frequencies and low noise severely restricts the design of millimeter wave circuits. The mixer is an indispensable component in the transceiver, and always needs enough linearity and low noise to ensure the performance of the whole system; therefore, based on the development requirement of modern communication, the down-mixer with high linearity and low noise broadband is designed, and has wide application prospect and value.

At present, the traditional double-balanced gilbert mixer is widely applied to a wireless transmitter, the circuit diagram of the traditional double-balanced gilbert mixer is shown in fig. 3, the structure has better gain and port isolation, but the influence of parasitic capacitance on a millimeter wave frequency band is more obvious, so that the working bandwidth is extremely limited, and the performances such as noise, linearity and the like are seriously deteriorated, so that the double-balanced gilbert mixer is not suitable for the application of millimeter waves, particularly E wave bands in the aspect of automobile anti-collision radars; therefore, under the vision of advanced auxiliary driving even unmanned driving, the mixer with high linearity, large bandwidth, low noise and low power consumption applied to the automobile anti-collision radar is designed, and has wide application prospect and value.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a mixer for an automotive anti-collision radar, which employs a transformer-coupled cascode circuit structure (TCCT) and is capable of improving linearity of the mixer, reducing noise, and increasing bandwidth without reducing other performances. In the invention, the transformer coupling is adopted to separate the direct current path configured by the cascode by the transformer, and independent bias is provided for the transconductance stage and the switching stage, so that the mixer can work under low voltage, and the bias of the transconductance stage is close to the third-order transconductance (gm) under the condition of not influencing the optimized noise bias of the switching stage₃) The zero crossing point is achieved, so that the linearity of the mixer is improved, the noise is reduced, and the circuit structure is symmetrical, so that the mixer is beneficial to the isolation degree when the actual layout is implemented.

In order to achieve the purpose, the invention adopts the technical scheme that:

a mixer for use in automotive anti-collision radars, comprising: the transformer comprises a transconductance stage unit 1, a transformer stub coupling unit 2, a switching stage unit 3, a load stage unit 4 and a buffer stage unit 5; the method is characterized in that:

the transconductance stage unit 1 comprises an NMOS tube M₁NMOS transistor M₂Wherein, the NMOS tube M₁NMOS transistor M₂Source electrodes are all grounded, and NMOS tube M₁A grid electrode is connected with a positive input end of a radio frequency signal, and an NMOS tube M₂The grid is connected with the negative input end of the radio frequency signal, and the NMOS tube M₁The drain electrode is connected with the preceding stage inductor L of the transformer₁Homonymous terminal and NMOS tube M₂The drain electrode is connected with the primary inductor L of the transformer₁A synonym terminal;

the transformer stub coupling unit 2 comprises a transformer T, two open-circuit stubs and a capacitor C₅And a capacitor C₆Wherein the transformer T is composed of a primary coil L₁And a secondary coil L₂Composition, primary coil L₁Is tapped at the center V_DDSecondary winding L₂Is grounded, and the secondary coil L₂Two ends of the short stub are respectively connected in series with an open-circuit stub, and the other ends of the two open-circuit stubs are respectively connected in series with a capacitor C₅Capacitor C₆To the ground;

the switch stage unit 3 comprises an NMOS tube M₃NMOS tube M₄NMOS transistor M₅And NMOS tube M₆Wherein, the NMOS tube M₄And NMOS transistor M₅Grid interconnection is connected with negative input end of local oscillator signal, and NMOS tube M₃And NMOS transistor M₆Grid interconnection is connected with positive input end of local oscillator signal and NMOS tube M₃And NMOS transistor M₄Transformer secondary inductance L of source electrode interconnection transformer coupling unit₂End of same name, NMOS tube M₅And NMOS transistor M₆Transformer secondary inductance L of source electrode interconnection transformer coupling unit₂Different name end, NMOS tube M₃And NMOS transistor M₅Is interconnected with the drain electrode of the NMOS tube M₄And NMOS transistor M₆The drain electrode of (a);

the load stage unit 4 comprises two identical inductors L₃、L₄(L₃＝L₄) And two identical capacitors C₃、C₄(C₃＝C₄) (ii) a Inductor L₃And a capacitor C₃Connected in parallel as a group, and one end of the power supply is connected with a power supply voltage V_DDThe other end is connected with an NMOS tube M₃NMOS transistor M₅The drain electrode of the first transistor is connected with and used as a positive output end of the intermediate frequency signal; inductor L₄And a capacitor C₄Connected in parallel to another group, one end of which is connected to the power supply voltage V_DDThe other end is connected with an NMOS tube M₄NMOS transistor M₆The drain electrode of the first transistor is connected with and used as a negative output end of the intermediate frequency signal;

buffer unit 5 includes that two the same transimpedance amplifiers place respectively at intermediate frequency signal positive output and intermediate frequency signal negative output, transimpedance amplifier comprises electric group, NMOS pipe, PMOS pipe and coupling capacitance, wherein, coupling capacitance one end is connected intermediate frequency signal output, the other end and is connected the electric group, and the resistance other end is as mixer intermediate frequency signal output, and NMOS pipe source ground connection, grid and drain-source are parallelly connected at the resistance both ends, and the grid stage of PMOS pipe is cascadedAnd the drain electrode is respectively correspondingly connected with the grid electrode and the drain electrode of the NMOS tube, and the source electrode is connected with the power supply voltage V_DD。

Further, in the mixer applied to the automobile anti-collision radar, all field effect transistors are replaced by bipolar transistors, specifically: the NPN type triode replaces an NMOS tube, and the PNP type triode replaces a PMOS tube.

From the working principle, the invention relates to a novel frequency mixer adopting a transformer-coupled cascode structure, which comprises a transconductance stage unit, a transformer stub coupling unit, a switch stage unit, a load stage unit and a buffer stage unit. The transconductance stage unit consists of a pair of differential pair NMOS tubes; the electromagnetic coupling unit consists of a transformer and open-circuit stub lines which are connected in series from two sides of a primary coil of the transformer to the ground, the transformer is arranged between the switching stage and the transconductance stage, a direct-current path configured by a cascade is separated by the transformer to provide independent bias for the transconductance stage and the switching stage, so that the mixer can work under low voltage to achieve the effect that the bias of the transconductance stage is close to third-order transconductance (gm) under the condition of not influencing the optimized noise bias of the switching stage₃) The zero crossing point is achieved, so that the linearity of the mixer is improved, the noise is reduced, and the switching stage unit mainly comprises four NMOS (N-channel metal oxide semiconductor) tubes and is biased in an optimal switching state; the load stage unit is directly composed of two capacitors and two inductors, so that the bandwidth can be increased and the gain can be improved; the differential intermediate frequency signal is amplified by the transconductance stage unit, is mixed with the local oscillator signal in the switch stage unit, and finally the differential radio frequency signal is output between the load stage unit and the switch stage unit; the buffer stage unit consists of an NMOS (N-channel metal oxide semiconductor) tube, a PMOS (P-channel metal oxide semiconductor) tube and an electric group, and enhances the output driving capability of the mixer.

The structure of the invention reduces the chip area occupied by the traditional matching, reduces the product cost, has the characteristics of high linearity, low noise and large bandwidth, is suitable for multi-standard millimeter wave radio application, and has wide application prospect on the advanced driving-assistant automobile anti-collision radar.

In summary, compared with the conventional gilbert up-mixer, the advantages and significant effects of the present invention are:

1. the transformer is in a structure of a cascode coupled by a short section line, the transformer is arranged between the switch stage and the transconductance stage, and a direct current path configured by the cascode is separated by the transformer to provide independent bias for the transconductance stage and the switch stage, so that three-order nonlinear transconductance of the transconductance stage is counteracted, and the linearity is improved;

2. in the E wave band, an electromagnetic coupling technology is combined with the open-circuit stub, parasitic capacitance and junction capacitance of a transconductance stage and a switch stage are offset, the problem of noise deterioration of the frequency mixer along with frequency rise is solved, noise is reduced, the two inductors are prevented from occupying a large chip area in the design of the frequency mixer, the chip area is saved, and the product cost is reduced;

3. the transformer coupling is adopted, the requirement of a traditional Gilbert structure on high power supply voltage can be overcome, the frequency mixer can work at low power supply voltage, the inductor and the capacitor load are adopted for output, the quality factor of the output inductor is optimized, and the middle frequency band width and the gain of the output inductor can be well compromised, so that the frequency mixer is suitable for multi-standard millimeter wave radio application.

Drawings

FIG. 1 is a schematic diagram of an E-band mixer circuit applied to an automotive anti-collision radar according to the present invention.

FIG. 2 shows 1V V in example 1 of the present invention_DSLower g_mExpansion coefficient of (a) with voltage V_GSThe graph is varied.

Fig. 3 is a schematic diagram of a conventional gilbert up-mixer circuit.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

The embodiment provides a novel E-band mixer adopting a transformer-coupled cascode structure technology, which is applied to an automobile anti-collision radar; the schematic circuit structure is shown in fig. 1, and includes: the transformer comprises a transconductance stage unit 1, a transformer stub coupling unit 2, a switching stage unit 3, a load stage unit 4 and a buffer stage unit 5; positive and negative ends V of differential radio frequency signal_RF+And V_RF-Injecting the transconductance unit 1, amplifying the signal by the transconductance unit 1 and outputting the amplified signal to the electromagnetic coupling unit2, output from the secondary winding of the transformer to the switching stage unit 3 via electromagnetic coupling, the switching stage unit 3 and the differential local oscillator input signal V_LO+And V_LO-Connected, differential intermediate frequency signal V_IF+And V_IF-The output is output from between the switch stage unit 3 and the load stage unit 4 and is output by the buffer stage unit 5 through capacitive coupling; more specifically:

the transconductance stage unit 1 comprises a pair of differential NMOS (N-channel metal oxide semiconductor) tube pairs M₁、M₂Forming a radio frequency differential input circuit structure; the NMOS tube M₁NMOS transistor M₂Source electrodes are all grounded, and NMOS tube M₁A grid electrode is connected with a positive input end of a radio frequency signal, and an NMOS tube M₂The grid is connected with the negative input end of the radio frequency signal, and the NMOS tube M₁The drain electrode is connected with the primary inductor L of the transformer₁Homonymous terminal and NMOS tube M₂The drain electrode is connected with the preceding stage inductor L of the transformer₁A synonym terminal; through reasonably designing the grid bias of the differential NMOS tube pair, the transconductance level can be biased to be close to third-order transconductance (gm)₃) The zero crossing point is used for offsetting the third-order nonlinear transconductance and improving the linearity;

the transformer stub coupling unit 2 comprises a transformer T, an open stub and a capacitor C₅、C₆The transformer T is composed of a primary coil L₁And a secondary coil L₂Composition, primary coil L₁Is tapped at the center V_DDSecondary winding L₂Is grounded, and the secondary coil L₂Two ends of the short stub are respectively connected in series, and the other end of the short stub is respectively connected in series with a capacitor C₅、C₆To the ground; the transformer is arranged between the switch stage and the transconductance stage, and the direct current path configured by the cascode is separated by the transformer to provide independent bias for the transconductance stage and the switch stage, so that the bottle mixing device can work under low voltage to achieve the effect that the bias of the transconductance stage is close to the third-order transconductance (gm) under the condition of not influencing the optimized noise bias of the switch stage₃) Zero crossing points, thereby improving the linearity of the mixer and reducing noise; by reasonably designing the open stub and the series capacitance, the parasitic capacitance and the junction capacitance of the transconductance stage and the switching stage are counteracted, the problem of noise deterioration of the mixer along with frequency increase is solved, and the noise is reduced;

the switch stage unit 3 comprises four NMOS tubes M₃～M₆(ii) a NMOS tube M₄And M₅Grid interconnection is connected with negative input end of local oscillator signal, and NMOS tube M₃And M₆Grid interconnection is connected with positive input end of local oscillator signal and NMOS tube M₃And M₄Transformer secondary inductance L of source electrode interconnection transformer coupling unit₂End of same name, NMOS tube M₅And M₆Transformer secondary inductance L of source electrode interconnection transformer coupling unit₂Different name end, NMOS tube M₃And M₅Is interconnected with the drain electrode of the NMOS tube M₄And M₆The drain electrode of (a); by optimizing four NMOS transistors M₃～M₆The size and the offset of the switch stage unit enable the switch stage unit to work in the optimal switch state, and nonlinearity caused by the switch tube is reduced;

the load stage unit 4 comprises two inductors L₃、L₄(L₃＝L₄) And two capacitors C₃、C₄(C₃＝C₄) (ii) a Inductor L₃And C₃Connected in parallel as a group, and one end of the power supply is connected with a power supply voltage V_DDThe other end is connected with an NMOS tube M₃And M₅The drain electrode of the first transistor is connected with and used as an intermediate-frequency positive output end; inductor L₄And C₄Connected in parallel to another group, one end of which is connected to the power supply voltage V_DDThe other end is connected with an NMOS tube M₄And M₆The drain electrode of the first transistor is connected with and serves as a medium-frequency negative output end; reasonable design load inductance L₃And C₃And L₄And C₄The value of (3) can well compromise the output intermediate frequency bandwidth and the gain;

the buffer stage unit 5 comprises two transimpedance amplifiers respectively placed at the positive end of the intermediate frequency signal output and the negative end of the intermediate frequency signal output, and the transimpedance amplifier at the positive end of the intermediate frequency signal output is composed of an electric group R₁An NMOS transistor M_B1And a PMOS transistor M_P1Composition of electric group R₁And a coupling capacitor C₁Connected NMOS transistor M_B1The source electrode is grounded, and the grid electrode and the drain electrode are connected in parallel to a resistor R₁Two-end PMOS transistor M_P1The grid and the drain of the NMOS transistor are respectively corresponding to the NMOS transistor M_B1The grid electrode is connected with the drain electrode,Source stage connection power supply voltage V_DD(ii) a The trans-impedance amplifier of the negative end of the intermediate frequency signal output consists of an electrical group R₂An NMOS transistor M_B2And a PMOS transistor M_P2Composition of electric group R₂And a coupling capacitor C₂Connected NMOS transistor M_B1The source electrode is grounded, and the grid electrode and the drain electrode are connected in parallel at the resistor R₂Two-end PMOS transistor M_P2The grid and the drain of the NMOS transistor are respectively connected with the NMOS transistor M_B2The grid is connected with the drain, and the source is connected with the power voltage V_DD(ii) a The buffer stage may increase the output drive capability of the mixer, particularly the ability to drive capacitive loads.

The structure of the invention can be realized by a field effect transistor and a bipolar transistor; when the bipolar transistor is used for realizing the transistor, only the NMOS tube needs to be replaced by the NPN type triode, and the PMOS tube needs to be replaced by the PNP type triode.

In terms of working principle: compared with the traditional Gilbert mixer, the invention has the advantages that the requirement of the circuit on the power supply voltage is reduced, the linearity and the noise performance are good in a millimeter wave frequency band, particularly an E wave band, the broadband characteristic is realized, and the invention is suitable for the fields of multi-standard millimeter wave radio application and automobile anti-collision radar.

More specifically:

1) the analysis of noise performance improvement, which is to qualitatively analyze the structure of the traditional Gilbert mixer with the introduced inductor shown in fig. 3, can obtain that the input reference noise voltage of the mixer is:

wherein, g_miIs M_iTransconductance of (C)_pIs the parasitic capacitance at node P, R_LTo output a load, I_n,M1And V_n,M2Is a transistor M₁And M₂K is the boltzmann constant and T is the thermodynamic temperature;

as can be seen from the above equation, the conversion gain of the mixer follows the parasitic capacitance C_pAnd thus the input reference noise becomes large, when the operating frequency is raised to millimeterThe effect of parasitic capacitances in the mixer becomes more severe at the band, resulting in greater RF current leakage between stages and overall noise performance degradation.

In order to overcome the above disadvantages, the present invention adopts a transformer-coupled cascode (TCCT) mixer, and analyzes the transformer stub coupling unit of the core in fig. 1, and after adopting the noise reduction transformer structure, the input reference noise voltage corresponding to the operating center frequency is:

from the above analysis, we can find that inserting the transformer network between the two stages of the mixer can effectively reduce noise and avoid the chip area from being too large.

2) Analysis of the linearity boost, third order transconductance g, as shown in FIG. 3_m3Playing an important role in the generation of nonlinear harmonics, IP3 can be expressed as:

wherein, g_m(n)Is the nth order transconductance of the transistor;

as can be seen from equation (3), the IP3 of the device can be reduced by reducing g_m3To improve, in FIG. 2, g_m3Having a zero crossing, g if the transconductance stage is biased near the zero crossing_m3The resulting nonlinear effects can be effectively mitigated. In the present invention, since TCCT provides independent biasing for two stages, g is avoided_m3Gate-source voltage V of oversized transconductance stage_GSBiased at a lower voltage.

While the invention has been described with reference to specific embodiments, any feature disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise; all of the disclosed features, or all of the method or process steps, may be combined in any combination, except mutually exclusive features and/or steps.