1.2 V, 12.5 MHz fourth‐order low‐pass filter with 83 dB stopband attenuation using low output impedance source follower in 45 nm CMOS

A source follower with improved output resistance is proposed. This improvement is achieved using shunt–shunt feedback with the help of a voltage combiner in the feedback loop which helps not only enhancing the gain but achieving reduced distortion due to improved isolation. A high-performance Sallen–Key biquad is implemented using this improved source follower and two capacitors which offer 29.3 MHz of bandwidth and almost 50 dB of stopband attenuation with the power of 2.3 mW. A fourth-order Chebyshev low-pass filter prototype is designed with a cascade of two such biquads in 45 nm complementary metal–oxide–semiconductor (CMOS). A cut-off frequency of 12.4 MHz is obtained with a stopband rejection of more than 83 dB. The power dissipation of the filter is 5.1 mW, at 1.2 V supply, and achieves an in-band third-order intercept point of +26.8 dBm. The in-band input-referred noise is 3.4 ( uV / Hz ) , resulting in a dynamic range of 78.1 dB.