A Tunable 0.2–1.2-GHz <i>N</i>-Path Bandpass Filter With Improved Harmonic and Out-of-Band Rejection

In this article, a novel cascaded <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i>-Path filter architecture is proposed to enhance both out-of-band rejection and harmonic rejection (HR) of conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i>-Path filter. An active gain-boosted <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i>-Path filter front end for signal amplification and noise suppression, and a passive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i>-Path filter with harmonic rejection switch backend provide high out-of-band and harmonic rejection and enhance linearity after cascade. The resulting filter is fabricated in a 180-nm process and operates under a six-phase nonoverlapping clock with a duty cycle of 16.7%. The measurement results show that in the tunable frequency range of 0.2–1.2 GHz, the filter achieves more than 32 dB of second and third harmonic rejections, a maximum of 55-dB out-of-band rejection, a bandwidth of 20–40 MHz, an in-band gain of 0–5dB, and an in-band matching of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S 11\lt -15$</tex-math> </inline-formula> dB. The in-band noise figure (NF) is 4.5–5.2 dB. As for linearity, the in-band P1dB is −2.8 to −0.9 dBm, and the out-of-band input third-order intercept point (OOB-IIP3) is +10.9 and +24.6 dBm at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times $</tex-math> </inline-formula> BW and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times $</tex-math> </inline-formula> BW, respectively. The entire filter consumes 12.6–23.4mW of power with an area of 0.45 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>.