采用PIN二极管反馈的射频可变增益放大器

Radio Frequency Variable Gain Amplifier with Variable Feedback of PIN Diode

射频可变增益放大器大多基于CMOS工艺和砷化镓工艺,通过改变晶体管的偏置电压或建立衰减器增益控制结构实现增益可调.本文采用高性能的射频锗硅异质结双极晶体管,设计并制作了一款射频可变增益放大器.放大器的增益可控性通过改变负反馈支路中PIN二极管的正向偏压来实现.基于带有PIN二极管反馈的可变增益放大器的高频小信号等效电路,本文详细分析了增益可控机制,设计并制作完成了1.8GHz的可变增益放大器.测试结果表明在频率为1.8GHz时,控制电压从0.6V到3.0V的变化范围内,增益可调范围达到15d B;噪声系数低于5.5d B,最小噪声系数达到2.6d B.整个控制电压变化范围内输入输出匹配均保持良好,线性度也在可接受范围内.

Most of the radio frequency（ RF） variable gain amplifiers（ VGA） are fabricated in CMOS process and Ga As process. The gain variability is usually realized when the biased voltage / current of transistors is changed or an attenuator in VGAs is built. A RF VGA variable gain amplifier based on high performance RF Si Ge heterojunction bipolar transistor（ HBT） is presented. The designed VGA consists of a feedback path with a PIN diode. The PIN diode forward resistance is controlled by its forward biased voltage,and hence the d B-linear variable gain is realized when the PIN diode forward biased voltage is altered. After the high-frequency small-signal equivalent circuit of the VGA with the PIN diode feedback is built,the gain controlling mechanism is analyzed. A complete design and implementation of a 1. 8GHz VGA with the proposed VGA topology was demonstrated. The test results showthat the dynamic gain scope reaches 15 d B at the frequency of1. 8GHz when the controlling voltage changes from 0. 6V to 3. 0V. The noise figure is lower than 5. 5d B and the minimum noise figure achieves 2. 6d B. The input and output matching keeps well and the linearity is also acceptable in the whole voltage variable range.