LOW-NOISE, LOW-DISTORTION CMOS AM WIDE-BAND AMPLIFIERS MATCHING A CAPACITIVE SOURCE

A low-noise, low-distortion AM wide-band CMOS amplifier is presented that matches a capacitive antenna. The amplifier uses a single-ended input stage to realize optimal noise matching with a capacitive source of 75 pF. The equivalent input noise voltage is as low as 0.7 μVrmsrms within 2.5-kHz IF bandwidth. A differential symmetrical class-AB output stage is optimized to large-signal distortion performance. With 8-V single power supply the amplifier is capable of driving a 7-Vpp/l-MHz signal into a 400-Ω load with a total harmonic distortion of 2%. A very high dynamic range of 130 dB has thus been achieved. An intermodulation-free dynamic range (IMFDR) up to 96 dB and an IM3 intercept of 18 Vpp have been measured. The amplifier is fabricated in a standard 3-μm n-well CMOS technology. Design details concerning noise, distortion, and stability performances are analytically described. © 1990 IEEE