Abstract: This paper presents the design of a variable gain amplifier with wideband and linear-in-dB gain control based on a TSMC 0.18μm RF CMOS process.The circuit of the amplifier consists of two gain stages.The first stage is a cascode amplifier with voltage-shunt negative feedback for good input impedance matching and noise figure performance.The second stage adopts the signal-summing structure to achieve gain control.A new exponential function circuit is added to solve the problem that the gain of amplifier and the control voltage is not a linear relationship,which caused by the non-exponential relationship between drain-source current and gate-source voltage,making the gain become linear in dB along with the control voltage.Measurement results show that the amplifier consumes 9mA at 1.8V.The 3dB bandwidth is 430~2330MHz.The circuit has a controllable gain range of -3.3~9.5dB.The noise figure is 6.2dB at maximum gain,and the input P1dB at minimum gain is -9dBm.

Key words: variable gain amplifier, CMOS, wideband, dB-linear