摘要
文章提出了一种宽带注入锁定三倍频器。在传统注入方式基础上,倍频器采用了推-推差分对输入信号进行二倍频,并将产生的二次谐波通过变压器耦合至注入管的源极共模点,增强了注入管源极共模点二次谐波。由于注入电流是由注入信号与源极共模点二次谐波进行混频而产生,因此注入电流也被增强,从而增大了锁定范围。除此之外,三倍频采用了四阶谐振器,谐振阻抗的相位在过零点被平坦化,锁定范围进一步被增大。采用标准CMOS 65 nm工艺设计三倍频,芯片面积为720×670 μ
从第一代通信发展至今,人们对通信速率的追求是无止尽的,当前广泛使用的第四代通信的中心为3 GHz。根据香农定
总体而言,倍频器有三种类型:器件非线性倍频
本文的倍频器用推-推差分对产生二次谐波并耦合至注入管源极共模点来增加该点二次谐波,从而增强注入电流,进而提升锁定范围。除此之外,还采用了多峰值(四阶)谐振器来增加锁定范围。
注入锁定倍频器的本质原理与注入锁定振荡器类似,当一个外部信号注入到振荡器时,只要这个外部信号足够强,并且频率与振荡器自由振荡频率足够近,振荡器将会偏离原来的频率而被迫与外部信号频率同步。注入锁定倍频器就是用输入信号的谐波去对振荡器进行锁定。
, | (1) |
对倍频器进行锁定从而实现倍频。

图1 (a) 注入锁定倍频器半边模型,(b) 相位图
Fig. 1 (a) Model of half circuit of the ILFM, (b) the corresponding phasor diagram
. | (2) |
二阶谐振器谐振阻抗的幅值和相位响应如

(a)

(b)
图2 二阶谐振器的阻抗幅值(a)和相位(b)
Fig. 2 Impedance magnitude (a) and phase (b) of the second-order resonator
本文研究的倍频器倍频比为3,即注入锁定三倍频 (Injection-Locked Frequency Tripler, ILFT)。

图3 传统注入锁定三倍频结构
Fig.3 Conventional injection-locked frequency tripler
针对现有三倍频的问题,本文提出一种带有四阶谐振器的二次谐波增强型注入锁定三倍频器。

图4 本文提出的三倍频器
Fig. 4 Proposed ILFT
(a)是推-推差分对,和偏置在阈值电压,当注入信号施加在差分对栅极时,差分对的漏极共模点(图中A点)产生输入信号的二次谐波;和是输入补偿线,能与寄生电容谐振增大输入电压强度,有助于提升倍频器带宽。(b)是变压器,由初级线圈和次级线圈组成,耦合系数为,A点二次谐波将会被变压器耦合至B点。由于变压器有信号叠加作用,B点二次谐波将会被增强。(c)是倍频器的差分注入管,在工作的时候,和类似于次谐波混频器,将栅极基波信号和B点二次谐波信号相混频,得到和两个频率分量。由于振荡器的谐振器谐振在,因此注入管混频后的分量将会被滤除,留下来锁定振荡器,从而实现了倍频。(f)是LC共源输出缓冲级,为倍频器提供反向隔离。
倍频器中的推-推管和注入管都利用了共模点产生二次谐波,其机理如

图5 二次谐波的产生
Fig. 5 Second harmonic generation

图6 注入管源极共模点波形
Fig. 6 Waveform at the common source node of the injectors

(a)

(b)

(c)
图7 (a) 注入管漏极电流瞬态波形, (b)传统倍频器和本文倍频器, (c)注入管漏极电流
Fig. 7 (a) Transient current waveform at the drains of the injectors, the currents at the drain nodes of the conventional tripler (b) and the proposed tripler (c)

图8 两种注入结构下的锁定范围
Fig. 8 The locking ranges corresponding to the two types of injection structure
文献 [
. | (3) |

图9 基于变压器的多峰值谐振器
Fig. 9 The transformer-based fourth-order tank
对四阶谐振器而言,最重要的是变压器的参数,调节合适的器件参数,可以实现宽带谐振,

图10 谐振器中的变压器尺寸
Fig. 10 Dimension of the transformer in the resonator

图11 谐振器变压器感值和耦合系数
Fig. 11 Inductance and coupling coefficient of the transformer in the resonator

(a)

(b)
图12 二阶与四阶谐振器的阻抗幅值(a)和相位(b)
Fig. 12 Impedance magnitude (a) and phase (b) of the second-order and fourth-order resonator

图13 三倍频器版图
Fig. 13 Layout of the proposed ILFT
本文电路性能参数主要通过Cadence平台的谐波平衡仿真得出。考虑到实际应用,倍频器的负载单端电阻为150~250 Ω,在仿真时设置成150 Ω。

图14 输入频率为7.8 GHz时的频谱
Fig. 14 Spectrum at 7.8 GHz input frequency

图15 灵敏度曲线
Fig. 15 Sensitivity curve

图16 单端输出电压幅度和功率
Fig. 16 Single-ended output amplitude and power
谐波抑制也是一个比较重要的参数,如果倍频器的输出包含比较强的谐波,会影响下级混频器的本振幅度平衡性,进而影响收发机性能。文献[

图17 谐波抑制比
Fig.17 Harmonic rejection ratios (HRRs)
本文提出了一种带有四阶谐振器的二次谐波增强型毫米波三倍频。在传统注入锁定三倍频器的基础上,在输入端与差分注入管并联增加了一对推-推差分对。本文的倍频器利用变压器将推-推差分对产生的二次谐波叠加到注入管源极共模点,增强了注入管源极共模点二次谐波,注入管产生的注入电流因此得到了提升,从而增加了锁定范围。同时,倍频器的核心振荡器采用了四阶谐振器,进一步提升了倍频器的带宽。该三倍频器可以用于5G通信的毫米波本振源以驱动混频器进行上下变频。
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