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设计了一种dB线性增益的数字控制可变增益放大器。以二极管做负载的全差分输入共源极放大器为原型,通过同时同比例地改变输入输出晶体管尺寸比和偏置电流比来控制增益变化,使输入输出晶体管的电流密度保持一恒定值,提高了电路在低增益时的线性度。电路采用NEC 0.35μm CMOS标准工艺库进行设计。仿真结果表明,dB线性增益范围为-11.85dB到11.64dB,增益误差小于0.5dB。增益为-11.85dB时,其1-dB压缩点达到8.35dBm,-3dB增益带宽大于62MHz,并且随设定的增益值在62MHz和240MHz之间变化。
A digital controlled variable gain amplifier with linear gain of dB is designed. A fully differential input common-source amplifier with a diode load is used as a prototype to control the gain variation by simultaneously changing the input / output transistor size ratio and the bias current ratio so that the current density of the input / output transistor is kept constant, increasing Linearity of the circuit at low gain. The circuit is designed with NEC 0.35μm CMOS standard library. The simulation results show that the linear gain range of dB is -11.85dB to 11.64dB and the gain error is less than 0.5dB. With a gain of -11.85dB, the 1-dB compression point reaches 8.35dBm, the -3dB gain bandwidth is greater than 62MHz, and varies with the set gain between 62MHz and 240MHz.