A 17 GHz inductorless low-pass filter based on a quasi-Sallen–Key approach

In this paper, an evolution of the Sallen-Key biquad architecture is presented, suitable for applications at very high frequency. The pole of the buffer amplifier is exploited as one of the poles of the biquad, therefore overcoming the constraints it poses on the maximum resonance frequency that can be achieved. This allows designing low-pass filters with cutoff frequencies above 10 GHz without using bulky inductors and with good linearity performance provided by the use of feedback. This approach has been exploited to design a biquad in a commercial SiGe BiCMOS technology with maximum fT$$ {f}_T $$ of about 320 GHz. The biquad has been designed to provide a resonance frequency f0$$ {f}_0 $$ of 12 GHz and a quality factor Q of 1.9; postlayout simulations show a cutoff frequency in excess of 17 GHz, 15.75 mW of power consumption, an equivalent input noise below 1 & mu;$$ \upmu $$Vrms, and -52 dB of total harmonic distortion (THD) for a 640 mVpp input signal, with a very limited area consumption.