CN112464605B - Optimization method of combined system of millimeter wave low noise amplifier and phase shifter - Google Patents

Abstract

A method for optimizing a combined system of a millimeter-wave low-noise amplifier and a phase shifter. By setting the transformer as the main part of the quadrature coupler in the combined system, the parallel capacitance required by the quadrature coupler and the initial value of the output impedance are calculated according to the operating frequency, Optimize the transformer feedback part of the LNA to maximize the square root n of the ratio of the equivalent inductances of the transformer two coils of the LNA and the coupling coefficient k ₁ , calculate the transconductance of the MOSFET under the optimal noise condition, and adjust the MOSFET DC bias point and size to make the The actual transconductance reaches the optimum value. Aiming at the shortcomings of the LNA and PS combined system and the VMPS, the invention combines the circuit structure of the LNA in the RFFE, realizes the broadband noise matching of the LNA by multiplexing the QHC, and generates a quadrature signal for vector modulation at the same time to realize the active phase shift. The purpose of saving area.

Description

Optimization method for combined system of millimeter wave low noise amplifier and phase shifter

technical field

The invention relates to a technology in the field of radio frequency communication, in particular to a combined design method of a millimeter-wave low-noise amplifier and a phase shifter based on the front of a quadrature coupler.

Background technique

When 5G mobile communication extends to the millimeter wave band, a multi-antenna phased array system needs to be used for beamforming to overcome the problem of millimeter wave space signal attenuation. The phase shifter (PS) is the core element of the phased array, and its resolution directly determines the resolution of the beamforming of the system. The mainstream RF phase shifters include various structures. Reflective Phase Shifters (RTPS) require no DC power consumption and can achieve continuous phase shifting, but with insufficient bandwidth and phase shifting range; Switching Phase Shifters (STPS) are another passive structure with good linearity but insertion loss The active vector synthesis phase shifter (VMPS) has high resolution, moderate area, and controllable insertion loss, but its bandwidth is still limited by the quadrature coupler. At the same time, the low noise amplifier (LNA) in the radio frequency front end (RFFE), the phase shifter and the antenna all require impedance matching, which brings additional area overhead and loss.

SUMMARY OF THE INVENTION

Aiming at the defects of the prior art, such as the low frequency and the additional noise effect caused by the unbalanced output of the quadrature coupler (QHC), the present invention proposes a combined system optimization method of a millimeter-wave low noise amplifier and a phase shifter. Combining the shortcomings of the system and VMPS, combined with the circuit structure of the LNA in the RFFE, the broadband noise matching of the LNA is realized by multiplexing the QHC, and the quadrature signal for vector modulation is generated at the same time to realize the active phase shift, so as to achieve the purpose of saving area.

The present invention is achieved through the following technical solutions:

By setting the transformer as the main part of the quadrature coupler in the combined system, the invention calculates the required parallel capacitance and the initial value of the output impedance of the quadrature coupler according to the operating frequency, and optimizes the transformer feedback part of the LNA to make the transformer two coils of the LNA, etc. The square root n of the ratio of the effective inductance and the coupling coefficient k ₁ are maximized, the transconductance of the MOSFET under the optimal noise condition is calculated, and the actual transconductance can reach the optimal value by adjusting the DC bias point and size of the MOSFET.

The combined system includes a quadrature coupler, a low-noise amplifier group and a programmable gain amplifier connected in sequence, wherein: the quadrature coupler generates I and Q two-way signals through a single-ended input and passes through a CG-level low-noise amplifier. Group amplification, modulated by a programmable gain amplifier, and then synthesized to output differential signals.

The equivalent inductance L3 _of the two coils of the transformer is the same and minimized while ensuring the maximum coupling coefficient.

Preferably, when the LNA and QHC are not amplitude matched, _n is decreased and gm is re-adjusted, and so on until the LNA and QHC amplitude matching conditions are met.

technical effect

The invention as a whole solves the problems that the bandwidth of the existing VMPS is greatly affected by the QHC or other polyphase generating networks, the impedance matching network between the LNA, the antenna and the VMPS brings a large insertion loss and area overhead, and the output imbalance of the QHC brings about. The problem of additional noise effects.

Compared with the prior art, the present invention inserts the LNA into the VMPS, and optimizes the noise and amplitude matching of the LNA input end, so that the QHC can simultaneously realize broadband impedance transformation, noise matching and quadrature signal generation, reducing additional LNA impedance matching. Network needs, saving area while increasing bandwidth. Due to subsequent PGA control, QHC for vector synthesis does not require precise calibration of the output. The invention connects the QHC with the LNA, avoids the noise caused by the insertion loss of the impedance matching network before the LNA, and at the same time makes a specific analysis on the noise matching of the LNA.

Description of drawings

Fig. 1 is the schematic diagram of LNA-PS system;

Figure 2 is a schematic diagram of the principle of QHC and the first-stage LNA;

Figure 3 is a schematic diagram of the transformer layout QHC;

In the figure: the input terminal IN, the through terminal THRU, the isolation terminal ISO, the coupling terminal CPL, the first to fourth metal layers 1 to 4, and the via hole 5;

Figure 4 is a schematic diagram of a noise circle such as an LNA;

Figure 5 is a schematic diagram of the QHC output phase and insertion loss;

Figure 6 is a schematic diagram of QHC return loss and output impedance;

FIG. 7 is a schematic diagram of the noise figure of the LNA-PS system before and after noise matching.

Detailed ways

As shown in FIG. 1 , this embodiment relates to a combined system, including a quadrature coupler QHC, a low noise amplifier group LNA and a programmable gain amplifier PGA connected in sequence, wherein: the quadrature coupler QHC is generated by a single-ended input The I and Q signals are amplified by the CG-level low-noise amplifier group LNA, modulated by the programmable gain amplifier PGA, and then synthesized to output differential signals.

The impedance matching between the low-noise amplifier group LNA and the programmable gain amplifier PGA is preferably achieved by using a two-turn or three-turn transformer.

As shown in FIG. 2 and FIG. 3 , the quadrature coupler QHC includes: a main body part and an input terminal IN, a straight-through terminal THRU, an isolation terminal ISO and a coupling terminal CPL respectively connected to it, and the main body part includes: QHC coils with the same equivalent inductance value and coupled to each other between the input terminal IN and the straight-through terminal THRU and between the isolation terminal ISO and the coupling terminal CPL are respectively arranged between the input terminal IN and the coupling terminal CPL and are arranged in The first capacitor with the same equivalent capacitance between the straight-through terminal THRU and the isolation terminal ISO, and the first capacitor with the same equivalent capacitance between the input terminal IN, the straight-through terminal THRU, the isolation terminal ISO, the coupling terminal CPL and the ground, respectively. Two capacitors.

The through end THRU and the coupling end CPL have a phase difference of (90±2)° and are respectively connected to two identical low noise amplifiers LNA.

其中：L₃为两个线圈的等效感值，k₂为两个线圈之间的耦合系数，R_s为QHC的特征阻抗，C₁和C₂分别为第一和第二电容的容值，从而保证奇模和偶模情况下电磁波传播速度相同。The QHC coil, the first capacitor and the second capacitor satisfy:

Where: L ₃ is the equivalent inductance of the two coils, k ₂ is the coupling coefficient between the two coils, R _s is the characteristic impedance of the QHC, C ₁ and C ₂ are the capacitances of the first and second capacitors, respectively , so as to ensure that the electromagnetic wave propagates at the same speed in the odd and even modes.

As shown in Figures 1 and 2, the CG-stage LNA group LNA includes two identical LNAs, and the negative feedback (-A) from the gate terminal to the source terminal is realized by using the transformer of the low noise amplifier, thereby Improve effective transconductance (Gm-boosting), reduce noise figure and DC power consumption.

其中：k₁为Gm-boosting低噪声放大器所用变压器的耦合系数，n为变压器中两线圈(图2中L₁和L₂)感值之比的平方根，g_m为MOSFET跨导，R_s为QHC的输出阻抗，γ为MOSFET的噪声参数，g_d0为漏源电压为0时的漏源电导，δ为MOSFET的栅极噪声系数，

ω为角频率，C_gs为MOSFET栅源寄生电容。Noise figure of each LNA

Where: k ₁ is the coupling coefficient of the transformer used in the Gm-boosting LNA, n is the square root of the ratio of the inductance values of the two coils (L ₁ and L ₂ in Figure 2) in the transformer, g _m is the MOSFET transconductance, and R _s is The output impedance of the QHC, γ is the noise parameter of the MOSFET, g _d0 is the drain-source conductance when the drain-source voltage is 0, δ is the gate noise coefficient of the MOSFET,

ω is the corner frequency, and C _gs is the MOSFET gate-source parasitic capacitance.

The feedback coefficient of the low noise amplifier is A=nk ₁ .

其中：α为g_m与g_d0之比，则对应的最小噪声系数

Optimal Quadrature Coupler Output Impedance with Minimum Noise Figure F _CG

Where: α is the ratio of g _m to g _d0 , then the corresponding minimum noise figure

It can be seen that the minimum noise can be reduced by increasing g _m or increasing A (ie nk ₁ ), the former can be achieved by adjusting the DC bias point and size of the MOSFET, and the latter can be achieved by enhancing the coupling of the transformer and increasing the equivalent inductance of the two coils ratio is realized. And considering that α is proportional to g _m , both methods will reduce R _s . At the same time, considering the effect of feedback on the input impedance, the input impedance of the LNA can be approximately expressed as 1/g _m and C _gs in parallel and divided by (1+A). Therefore, both methods will reduce the output impedance of the LNA, which makes noise matching and amplitude matching not contradictory.

To sum up, the optimization method of the QHC and LNA combined system involved in this embodiment includes the following steps:

The first step is to design a process-realizable transformer as the main part of the QHC, so that the equivalent inductance L ₃ of the two coils is the same and as small as possible, and the coupling coefficient is guaranteed to be greater than 0.7.

The second step is to calculate the parallel capacitance required by the quadrature coupler according to the current operating frequency.

The third step is to calculate the output impedance of the quadrature coupler as an initial value according to the current operating frequency.

In the fourth step, the transformer that can be realized by the design process is used as the feedback part of the first-stage MOSFET of the LNA, so that the square root n of the ratio of the equivalent inductance of the two coils is as large as possible, and the coupling coefficient k ₁ is greater than 0.75.

The fifth step is to calculate the transconductance g _m,opt of the MOSFET under optimal noise, and make g _m and g _{m, opt} equal by increasing the DC bias voltage of the gate terminal of the MOSFET and increasing the aspect ratio.

In the sixth step, when the LNA input impedance is different from the optimal QHC output impedance, go back to the fourth step and reduce n with a typical step size of 0.05, and so on until the LNA input impedance and the optimal QHC output impedance are satisfied.

As shown in FIG. 3, it is the basic structure of the quadrature coupler realized according to the above method, wherein the coil arranged between the input end IN and the through end THRU is composed of metal 1 and metal 3, and is arranged at the isolation end ISO and the coupling end The coil between the CPLs is composed of metal 2 and metal 4 . The equivalent inductance of the two coils is the same, and the two layers of metal of the same coil are connected by vias 5 .

The total thickness of the two coils needs to be as close as possible, so that the equivalent inductance values of the two coils are the same. To increase the coupling coefficient, the width of the coil is set to 1/5 of the inner diameter of the transformer.

After specific practical experiments, under the specific environment setting of the working frequency of 30GHz, the above method is run with R _s =10Ω, k ₂ =0.73, L ₃ =58pH parameters, and the results when the design is completed are shown in Figures 4 to 6 .

The described noise matching results are shown in Figure 4, where the LNA input impedance curve is tangent to the circle with a noise figure of 2.5dB.

The output phase and insertion loss results of the QHC are shown in Figure 5. Within a phase error range of 1°, the QHC's operating frequency range is 10GHz to 40GHz. When the insertion loss of the two outputs is the same, they are both 3.5dB. Since the subsequent two channels are vector synthesized to compensate the 3dB gain, this structure brings an additional 0.5dB loss.

The broadband impedance transformation characteristics of the QHC are shown in Figure 6. When the characteristic impedance changes from 10 ohms to 70 ohms, when f=30GHz, the return loss is always kept below -17dB, which proves that the structure can be adjusted according to needs. characteristic impedance.

The noise figure of the LNA-PS system before and after noise matching is shown in Figure 7, k ₁ =0.79, n = 1.71, L ₁ =320pH, L ₂ =110, the 3-dB bandwidth of the LNA-PS system is 26-34GHz, at 32GHz The minimum noise figure is 5.2dB. The minimum noise figure of this structure is 5.2dB, which is 6.2dB lower than the case of LNA and QHC independent design and direct connection without noise matching.

In this embodiment, for the specified characteristic impedance, combined with the structure of FIG. 3, the current process is used to select the metal layer with the closest total thickness, so that the equivalent inductance of the two coils is the same and as low as possible, and at the same time, the coupling coefficient as high as possible is achieved; it is achieved by iterative optimization. The QHC and LNA achieve simultaneous amplitude and noise matching.

The above-mentioned specific implementation can be partially adjusted by those skilled in the art in different ways without departing from the principle and purpose of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above-mentioned specific implementation. Each implementation within the scope is bound by the present invention.

Claims (10)

1. A method for optimizing the combined system of millimeter-wave low-noise amplifier and phase shifter features that a transformer is used as the main part of orthogonal coupler in said combined system, the parallel capacitance and initial output impedance value needed by said orthogonal coupler are calculated according to working frequency, and the feedback part of LNA is optimized to make the square root n of equivalent inductance ratio of two windings of LNA's transformer and coupling coefficient k ₁ Maximizing, calculating the transconductance of the MOSFET under the condition of optimal noise, and adjusting the direct current bias point and the size of the MOSFET to enable the actual transconductance to reach the optimal value;

the combined system comprises a quadrature coupler QHC, a low noise amplifier group LNA and a programmable gain amplifier PGA which are connected in sequence, wherein: the quadrature coupler generates I, Q two paths of signals through single-end input, amplifies the signals through a CG-level low-noise amplifier group, and synthesizes and outputs differential signals after being modulated by a programmable gain amplifier.

2. The millimeter wave low noise amplifier and phase shifter combined system optimization method of claim 1,it is characterized in that two coils of the transformer are equivalent to an inductor L ₃ Identical and minimized while ensuring maximum coupling coefficient.

3. The method of claim 1 or 2, wherein when the LNA and the quadrature coupler are not amplitude matched, the n is reduced and the MOSFET transconductance g is readjusted _m And so on until the condition that the LNA is matched with the quadrature coupler in amplitude is met.

4. The method of optimizing a combined millimeter wave low noise amplifier and phase shifter system of claim 1, wherein said quadrature coupler comprises: the main body part and input end IN, straight-through end THRU, isolation end ISO and coupling end CPL connected with the main body part respectively, the main body part includes: the QHC coils are respectively arranged between the input end IN and the straight-through end THRU, between the isolation end ISO and the coupling end CPL, have the same equivalent inductance value and are mutually coupled, the first capacitors are respectively arranged between the input end IN and the coupling end CPL and between the straight-through end THRU and the isolation end ISO, and the second capacitors are respectively arranged between the input end IN, the straight-through end THRU, the isolation end ISO and the coupling end CPL and the ground and have the same equivalent capacitance value.

5. The method as claimed in claim 4, wherein the phase difference between the straight-through terminal THRU and the coupling terminal CPL is (90 ± 2) °, and the two terminals are connected to two same low noise amplifiers LNA respectively.

6. The optimization method for the combined system of the millimeter wave low noise amplifier and the phase shifter as claimed in claim 3, wherein the QHC coil, the first capacitor and the second capacitor satisfy: angular frequency

Wherein: l is ₃ Is a two-coil equivalent inductance, k ₂ Is the coupling coefficient between the two coils, Rs is the characteristic impedance of QHC, C ₁ And C ₂ The capacitance values of the first capacitor and the second capacitor are respectively, so that the electromagnetic wave propagation speed is ensured to be the same under the conditions of an odd mode and an even mode.

7. The optimization method of the combined system of millimeter wave low noise amplifier and phase shifter as claimed in claim 3, wherein said CG low noise amplifier set LNA comprises two identical low noise amplifiers, and negative feedback-A from gate end to source end is realized by using the transformer of the low noise amplifiers, thereby improving effective transconductance Gm-boosting, and reducing noise figure and DC power consumption.

8. The method of claim 7 wherein the noise figure of each LNA is determined by the phase shifter

Wherein: k is a radical of ₁ Coupling coefficient, g, of a transformer for a Gm-boosting low noise amplifier _m Is MOSFET transconductance, R _s Is the output impedance of QHC, γ is the noise parameter of the MOSFET, g _d0 Is the drain-source conductance at a drain-source voltage of 0, delta is the gate noise figure of the MOSFET,

omega is angular frequency, C _gs Is the parasitic capacitance of MOSFET gate source.

9. The method as claimed in claim 7, wherein the feedback coefficient A of the LNA is nk ₁ 。

10. The millimeter wave low noise amplifier and phase shifter of claim 8Method for optimizing a combined system, characterized in that when the noise factor F is exceeded _CG Minimum optimum quadrature coupler output impedance

Wherein: alpha is g _m And g _d0 Ratio of the noise to the noise, the corresponding minimum noise figure

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