一种具备自动增益控制功能的宽带正交解调器

A Wideband Orthogonal Demodulator with Auto Gain Control

为了实现无线电接收机对多个通信标准的兼容和对信号链路增益的自动调节,提出了一种适用于宽带(0.8~2.7GHz)接收机并具备自动增益控制(AGC)功能的正交解调器。该解调器的信号主路上采用一个宽带设计的射频可变增益放大器和一个中频可变增益放大器,频率变换则通过一个增益可调的吉尔伯特单元实现。在信号反馈环路上采用一个均方根功率检波器检测输出信号的幅度并转换成直流电压,然后通过检波器输出的直流电压控制主路上各个模块的增益,从而形成一个AGC闭环系统。该解调器仅采用模拟电路实现AGC功能,避免了传统数字辅助型AGC需要大量端口、算法实现复杂和精度受有限步长的限制等缺点。该解调器在0.18μm BiCMOS工艺平台下设计并流片验证,测试结果表明:在0.8~2.7GHz内,正交解调器的可调转换增益范围为-36~36dB,解调带宽为100MHz;最大增益下噪声系数为9dB,正交相位误差1.6°,幅度误差为0.9dB。

An orthogonal demodulator with auto gain control(AGC)function for wideband(0.8-2.7 GHz)receivers is proposed to realize the compatibility of receivers to multi-mode wireless communication standards and the AGC in the signal path.The demodulator adopts a wideband RF variable gain amplifier and an IF variable gain amplifier in the main signal path,while the frequency translation is performed by using a variable gain Gilbert cell.A root-mean-square(RMS)power detector is designed in the feedback path to detect the amplitude of output signal and then transfer it to a dc voltage.An AGC close loop system is formed through controlling the gain of blocks in the main path by the output voltage of the power detector.The demodulator just adopts analog circuits to realize AGC function,and avoids the drawbacks of traditional digitalassisted AGC mechanism,such as much more pins,complex algorithms and limited resolution resulted from a finite step length.The demodulator is implemented with 0.18 μm BiCMOS technology.Measurement results show that when the operation frequency is within 0.8 GHz to 2.7 GHz,the tunable conversion gain range of the demodulator is from-36 dB to 36 dB,and the demodulation bandwidth is 100 MHz;When the gain is in maximum,the noise figure is 9 dB,theerror of the orthogonal phase is 1.6 degree and the error of the amplitude is 0.9 dB.