CN110677128A - An E-band Mixer Used in Automotive Collision Avoidance Radar - Google Patents

Abstract

The invention belongs to the technical field of wireless communication, and relates to automobile anti-collision radar, in particular to a mixer applied to automobile anti-collision radar, comprising: a transconductance level unit, a transformer stub coupling unit, a switch level unit, and a load level unit , buffer level unit. The invention adopts a cascode structure coupled with transformer stubs, the transformer is placed between the switching stage and the transconductance stage, and the DC path of the cascode configuration is separated by the transformer, which provides the transconductance stage and the switching stage. The independent bias can offset the third-order nonlinear transconductance of the transconductance stage and improve the linearity; at the same time, the electromagnetic coupling technology combined with the open stub in the E-band can offset the parasitic capacitance and junction of the transconductance stage and the switching stage. Capacitors can solve the problem of mixer noise deterioration as the frequency increases, reduce noise, and avoid introducing these two inductors in the mixer design, which will occupy a large chip area, save chip area, and reduce product costs.

Description

An E-band Mixer Used in Automotive Collision Avoidance Radar

technical field

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

Background technique

In recent years, with the rapid development of wireless communication technology, various wireless transceivers are developing to higher working frequency bands in pursuit of higher bandwidth, data rate, lower delay, millimeter wave (millimeter wave) frequency has attracted widespread attention. New products and services have emerged with huge market potential. For example, in the development of ultra-high-speed and ultra-high-frequency WLAN systems, the 60GHz 802.11ad communication system and LTE network technology are combined through the LWA network. For an excellent user experience, wireless fiber access is realized in the E-band (71-75GHz, 81-85GHz and 92-95GHz), as well as 77GHz advanced collision avoidance radar for assisted driving. For these applications, the fabrication of mmWave devices based on CMOS processes is attractive with high integration and low cost; however, the poor linearity of the devices at high frequency and low noise severely restricts the design of mmWave circuits. The mixer is an essential part of the transceiver, it always needs sufficient linearity and low noise to ensure the performance of the whole system; therefore, based on the development requirements of modern communication, a high linearity and low noise is designed. The broadband down-mixer has broad application prospect and value.

At present, the traditional double-balanced Gilbert mixer is widely used in wireless transmitters. Its circuit diagram is shown in Figure 3. This structure has good gain and port isolation, but it is in the millimeter wave frequency band due to parasitic capacitance. The impact of the millimeter wave is becoming more and more obvious, the working bandwidth is extremely limited, and the performance of noise and linearity is seriously deteriorated, so it is no longer suitable for the application of millimeter wave, especially the E-band, in the application of automotive anti-collision radar; it can be seen that in advanced assisted driving and even Under the vision of unmanned driving, designing a mixer with high linearity, large bandwidth, low noise and low power consumption for automotive anti-collision radar has broad application prospects and value.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the above problems, and propose a mixer applied to automobile anti-collision radar. The mixer adopts a transformer-coupling cascode topology (TCCT), which can Improve mixer linearity, reduce noise, and increase bandwidth without compromising other performance. In the present invention, transformer coupling is used to separate the DC path of the cascode configuration by the transformer, so as to provide independent bias for the transconductance stage and the switch stage, so that the mixer can work under low voltage and achieve the transconductance stage. The bias is close to the third-order transconductance (gm ₃ ) zero-crossing point without affecting the optimal noise bias of the switching stage, thereby improving the linearity of the mixer and reducing the noise. In addition, the symmetry of the circuit structure can be implemented in the actual layout. to good symmetry which benefits the isolation of the mixer.

To achieve the above object, the technical scheme adopted in the present invention is:

A mixer applied to automobile anti-collision radar, comprising: a transconductance stage unit 1, a transformer stub coupling unit 2, a switch stage unit 3, a load stage unit 4 and a buffer stage unit 5; it is characterized in that:

The transconductance stage unit 1 includes an NMOS transistor M ₁ and an NMOS transistor M ₂ , wherein the sources of the NMOS transistor M ₁ and the NMOS transistor M ₂ are both grounded, and the gate of the NMOS transistor M ₁ is connected to the positive terminal of the radio frequency signal input, and the NMOS transistor M 1 is connected to the positive terminal of the radio frequency signal input. The gate of the tube _M2 is connected to the negative input terminal of the radio frequency signal, the drain _of the NMOS tube M1 is connected to the same name terminal of the transformer front _- stage inductance L1, and the drain of the NMOS tube _M2 is connected to the same name terminal _of the transformer primary inductance L1;

The transformer stub coupling unit 2 includes a transformer T, two open-circuit stubs, a capacitor C ₅ and a capacitor C ₆ , wherein the transformer T is composed of a primary coil L ₁ and a secondary coil L ₂ , and the primary coil L The center tap of ₁ is connected to V _DD , the center tap of the secondary coil L ₂ is grounded, the two ends of the secondary coil L ₂ are connected in series with an open-circuit stub, and the other ends of the two open-circuit stubs are connected in series with capacitors C ₅ and C respectively. ₆ to the ground;

The switch stage unit 3 includes an NMOS transistor M ₃ , an NMOS transistor M ₄ , an NMOS transistor M ₅ and an NMOS transistor M ₆ , wherein the gates of the NMOS transistor M ₄ and the NMOS transistor M ₅ are connected to the negative input end of the local oscillator signal, and the NMOS transistor M 4 and the NMOS transistor M 5 are connected to the negative input terminal of the local oscillator signal. The gates of the transistor M3 and the NMOS transistor _M6 are connected to the positive input terminal of the local oscillator signal, the source electrodes _of the NMOS transistor M3 and the NMOS transistor M4 are connected to the same name terminal _of the transformer secondary inductance _L2 of the transformer coupling unit, and the _NMOS transistors _M5 and _The source electrode of the NMOS transistor _M6 is connected to the different terminal of the transformer coupling unit transformer secondary inductance L2, the drain electrode of the NMOS transistor M3 and the NMOS transistor _M5 is interconnected, and the drain electrode _of the NMOS transistor M4 and the NMOS transistor _M6 is interconnected _;

The load stage unit 4 includes two identical inductors L ₃ , L ₄ (L ₃ =L ₄ ) and two identical capacitors C ₃ , C ₄ (C ₃ =C ₄ ); the inductor L ₃ and the capacitor C ₃ are connected in parallel as One group, one end is connected to the power supply voltage V _DD , the other end is connected to the drains of the NMOS transistor M ₃ and the NMOS transistor M ₅ and is used as the positive output end of the intermediate frequency signal; the inductor L ₄ and the capacitor C ₄ are connected in parallel to form another group, and one end is connected to the power supply voltage V _DD , the other end is connected to the drains of NMOS transistor M ₄ and NMOS transistor M ₆ and is used as the negative output end of the intermediate frequency signal;

The buffer stage unit 5 includes two identical transimpedance amplifiers respectively placed at the positive output end of the intermediate frequency signal and the negative output end of the intermediate frequency signal. One end of the coupling capacitor is connected to the output terminal of the intermediate frequency signal, and the other end is connected to the electric group. The other end of the resistor is used as the output terminal of the intermediate frequency signal of the mixer. The stage and the drain stage are respectively connected to the gate and drain of the NMOS transistor correspondingly, and the source stage is connected to the power supply voltage V _DD .

Further, in the mixer applied to the automotive anti-collision radar, all field effect transistors are replaced by bipolar transistors, specifically: NPN transistors replace NMOS transistors, and PNP transistors replace PMOS transistors.

In terms of working principle, the present invention relates to a novel transformer-coupled cascode structure mixer, which includes a transconductance stage unit, a transformer stub coupling unit, a switch stage unit, and a load stage unit. , buffer level unit. The transconductance stage unit is composed of a pair of differential pair NMOS tubes; the electromagnetic coupling unit is composed of a transformer and an open-circuit stub connected in series on both sides of the primary coil of the transformer to the ground, and the transformer is placed between the switching stage and the transconductance stage. , The DC path of the cascode configuration is separated by the transformer, providing independent biasing for the transconductance stage and the switching stage, so that the mixer can work at low voltage, so that the biasing of the transconductance stage does not affect the switching stage The optimized noise bias is close to the zero-crossing point of the third-order transconductance (gm ₃ ), thereby improving the linearity of the mixer and reducing the noise. The switch stage unit is mainly composed of four NMOS transistors, and the bias is at the optimum The load stage unit is directly composed of two capacitors and two inductors, which can increase the bandwidth and increase the gain; the differential intermediate frequency signal is amplified by the transconductance stage unit, and the switch stage unit is connected to the local oscillator. The signal is mixed, and finally the differential radio frequency signal is output between the load stage unit and the switch stage unit; the buffer stage unit is composed of an NMOS transistor, a PMOS transistor and an electrical group to enhance 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, and is suitable for multi-standard millimeter wave radio applications, and is used in advanced assisted driving car anti-collision radar. There are broad application prospects.

To sum up, compared with the traditional Gilbert up-mixer, the advantages and significant effects of the present invention are:

1. The cascode structure coupled with transformer stubs is adopted. The transformer is placed between the switching stage and the transconductance stage. The DC path of the cascode configuration is separated by the transformer, which provides the transconductance stage and the switching stage. Independent bias, offset the third-order nonlinear transconductance of the transconductance stage, and improve linearity;

2. In the E-band, the electromagnetic coupling technology is combined with the open-circuit stub to offset the parasitic capacitance and junction capacitance of the transconductance stage and the switching stage, solve the problem of the deterioration of the mixer noise as the frequency increases, reduce the noise, and avoid Introducing these two inductors in the mixer design will occupy a large chip area, save chip area and reduce product cost;

3. The use of transformer coupling can overcome the traditional Gilbert structure's requirement for high power supply voltage, so that the mixer can work at low power supply voltage, and the output uses inductance plus capacitive load to optimize the quality factor of the output inductance, which can be better discounted. output IF bandwidth and gain in the range for multi-standard mmWave radio applications.

Description of drawings

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

FIG. 2 is a graph showing the variation of the expansion coefficient of g _m with the voltage V _GS under 1V V _DS in the embodiment of the present invention.

Figure 3 is a schematic diagram of a conventional Gilbert up-mixer circuit.

Detailed ways

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

This embodiment proposes a new E-band mixer using transformer-coupled cascode structure technology, which is applied to automobile anti-collision radar; the schematic diagram of its circuit structure is shown in Figure 1, including: transconductance stage unit 1, Transformer stub coupling unit 2, switch stage unit 3, load stage unit 4 and buffer stage unit 5; the positive and negative ends of the differential radio frequency signal V _RF+ and V _RF- are injected into the transconductance stage unit 1, passing through the transconductance stage unit 1 The amplified signal is then output to the primary coil of the electromagnetic coupling unit 2, and is output from the secondary coil of the transformer to the switch stage unit 3 through electromagnetic coupling. The switch stage unit 3 is connected to the differential local oscillator input signals V _LO+ and V _LO- , and the differential intermediate frequency signal V _IF+ and V _IF- are output from the switch stage unit 3 and the load stage unit 4, and are output by the buffer stage unit 5 through capacitive coupling; more specifically:

The transconductance stage unit 1 includes a pair of differential NMOS transistor pairs M ₁ and M ₂ to form a radio frequency differential input circuit structure; the sources of the NMOS transistor M ₁ and the NMOS transistor M ₂ are both grounded, and the gate of the NMOS transistor M ₁ is connected to the ground. The positive terminal of the RF signal input, the gate of the NMOS tube _M2 is connected to the negative input terminal of the RF signal, the drain of the NMOS tube M1 is connected to the same name terminal _of the primary inductance L1 _of the transformer, and the drain of the NMOS tube _M2 is connected to the same name of the transformer front _- stage inductance L1. By reasonably designing the gate bias of the differential NMOS transistor pair, the transconductance stage can be biased close to the zero-crossing point of the third-order transconductance (gm ₃ ) to cancel the third-order nonlinear transconductance and improve the linearity;

The transformer stub coupling unit 2 includes a transformer T, an open-circuit stub, and capacitors C ₅ and C ₆ . The transformer T is composed of a primary coil L ₁ and a secondary coil L ₂ , and the center tap of the primary coil L ₁ is connected to the center tap. V _DD , the center tap of the secondary coil L ₂ is grounded, the two ends of the secondary coil L ₂ are connected in series with open-circuit stubs respectively, and the other ends of the open-circuit stubs are connected in series with capacitors C ₅ and C ₆ respectively to the ground; the transformer is placed in the switching stage And between the transconductance stage, the DC path of the cascode configuration is separated by the transformer, which provides independent bias for the transconductance stage and the switching stage, so that the mixer can work at low voltage and achieve the transconductance stage bias. It is placed close to the third-order transconductance (gm ₃ ) zero-crossing point without affecting the optimal noise bias of the switching stage, thereby improving the linearity of the mixer and reducing the noise; Can offset the parasitic capacitance and junction capacitance of the transconductance stage and switching stage, solve the problem of the noise deterioration of the mixer as the frequency increases, and reduce the noise;

The switch stage unit 3 includes four NMOS transistors M ₃ to M ₆ ; the gates of the NMOS transistors M ₄ and M ₅ are connected to the negative input terminal of the local oscillator signal, and the gates of the NMOS transistors M ₃ and M ₆ are connected to the local oscillator signal. _The positive input terminal _of the NMOS tube M3 and _M4 is connected to the source of the transformer coupling unit transformer secondary inductance L2 with the same name, the source of the NMOS tube _M5 and _M6 is connected to the transformer coupling unit transformer secondary _inductance L2 is the same name terminal, the drains of NMOS transistors M3 and _M5 are interconnected, and the drains _of NMOS transistors M4 and _M6 are interconnected _; by optimizing the size and bias of the _four NMOS transistors M3- _M6 , the switch-level unit can work at the most The best switching state, reducing the nonlinearity introduced by the switching tube;

The load stage unit 4 includes two inductors L ₃ and L ₄ (L ₃ =L ₄ ) and two capacitors C ₃ and C ₄ (C ₃ =C ₄ ); the inductors L ₃ and C ₃ are connected in parallel to form a group, One end is connected to the power supply voltage V _DD , the other end is connected to the drains of the NMOS transistors M ₃ and M ₅ and is used as the positive output terminal of the intermediate frequency; the inductors L ₄ and C ₄ are connected in parallel to form another group, one end is connected to the power supply voltage V _DD , the other end is connected to _The drains of NMOS transistors M4 and _M6 are connected and used as the negative output terminal of the intermediate frequency _; the reasonable design _of the load inductances L3 and C3 and the values _of L4 and _C4 can better compromise the output intermediate frequency bandwidth and gain;

The buffer stage unit ₅ includes two _{transimpedance} amplifiers respectively placed at the positive terminal of the intermediate frequency signal output and the negative terminal of the intermediate frequency signal output. It is composed of a PMOS transistor M _P1 , the electrical group R ₁ is connected to the coupling capacitor C ₁ , the source level of the NMOS transistor M _B1 is grounded, the gate and the drain level are connected to both ends of the resistor R ₁ in parallel, the gate level and the drain level of the PMOS transistor M _P1 They are respectively connected to the gate and drain of the NMOS transistor M _B1 , and the source level is connected to the power supply voltage V _DD ; the transimpedance amplifier at the negative end of the intermediate frequency signal output is composed of an electrical group R ₂ , an NMOS transistor M _B2 and a PMOS transistor M It is composed of _P2 , the electric group R2 is connected to the coupling capacitor _C2 , the source stage of the NMOS tube M _B1 is grounded, the gate and the drain stage are connected to the _two ends of the resistor R2 in _parallel , the gate stage and the drain stage of the PMOS tube M _P2 are respectively connected with the NMOS tube The gate and drain of M _B2 are connected, and the source is connected to the supply voltage V _DD ; the buffer stage can increase the output drive capability of the mixer, especially the capability of driving capacitive loads.

The structure of the present invention can be realized not only with field effect transistors, but also with bipolar transistors; when realized with bipolar transistors, it is only necessary to replace NMOS transistors with NPN transistors and PMOS transistors with PNP transistors.

In terms of working principle: compared with the traditional Gilbert mixer, the invention realizes that the circuit has a lower requirement on the power supply voltage, has good linearity and noise performance in the millimeter wave band, especially the E band, and achieves broadband characteristics at the same time. Multi-standard mmWave radio applications and automotive collision avoidance radar fields.

To be more specific:

1) Analysis of noise performance improvement. Qualitative analysis of the structure of the traditional Gilbert mixer with inductance introduced in Figure 3 shows that the input reference noise voltage of the mixer is:

where _gmi is the transconductance of _Mi , _Cp is the parasitic capacitance at node P, _RL is the output load, In _{, M1} and Vn _{, M2} are the noise _of transistors M1 and _M2 , and k is Bohr Zman constant, T is the thermodynamic temperature;

It can be seen from the above formula that since the conversion gain of the mixer decreases with the increase of the parasitic capacitance C _p , the input reference noise becomes larger. When the operating frequency increases to the millimeter-wave frequency band, the parasitic The effect of capacitance can become more severe, resulting in greater RF current leakage between stages and overall noise performance degradation.

In order to overcome the above shortcomings, the present invention adopts the transformer-coupling cascode topology (TCCT) mixer, which can be obtained by analyzing the core transformer stub coupling unit in FIG. 1 , After adopting the noise reduction transformer structure, the input reference noise voltage at the corresponding operating center frequency is:

According to the above analysis, we can conclude that inserting the transformer network between the two stages of the mixer can effectively reduce noise and avoid excessive chip area.

2) Analysis of linearity improvement, as shown in Figure 3, the third-order transconductance g _m3 plays an important role in the generation of nonlinear harmonics, and IP3 can be expressed as:

Among them, g _m(n) is the nth order transconductance of the transistor;

It can be seen from equation (3) that the IP3 of the device can be improved by reducing _gm3 . In Figure 2, _gm3 has a zero-crossing point. If the transconductance stage is biased near the zero-crossing point, the _gm3 pair produces The nonlinear effects of can be effectively mitigated. In the present invention, since the TCCT provides independent biasing for the two stages, the gate-source voltage V _GS of the stage is biased to a lower voltage in order to avoid excessive transconductance of g _m3 .

The above descriptions are only specific embodiments of the present invention, and any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All steps in a method or process, except mutually exclusive features and/or steps, may be combined in any way.

Claims (2)

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.

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