A new Q-enhancement architecture for SAW-less communication receiver in 65-nm CMOS

Abstract

A 2.5V second order RF bandpass filter is presented. A new Q-enhancement structure stacked on a LNA is fabricated in a 65-nm CMOS process with a die area of 1.1 mm x 1.1 mm. The frequency range is adjustable in a 25% range from 1.7 GHz to 2.2 GHz while the Q is adjustable up to 50. Q and the center frequency are adjusted by binary weighted switchable capacitors. The filter draws 42 mA including the buffers from a 2.5 V supply and has an input referred out-of-band 1-dB compression point of 0 dBm. The measured in-band NF is between 5.4 and 6.2 dB.

An Active Feedback Interference Cancellation Technique for Blocker Filtering in RF Receiver Front-Ends

“…On the other hand, the estimated phase noise at the upconversion mixer is increased by 10 dB at 20 MHz offset frequency in comparison to the phase noise of the Rohde & Schwarz SMJ100A Vector Signal Generator which has been used as the local oscillator in the measurement setup. Apparently, this is a worst case estimate as other nonlinear effects that might influence noise figure degradation at high blocker levels are not accounted for in the loop excess noise (9). Nonetheless, this indicates that an overall improvement of the desensitization performance especially at low offset frequencies can be obtained by optimizing the LO path for lower phase noise.…”

“…The blocker replica extracted by highpass filtering in the baseband mixes with the LO phase noise tail thus resulting in a transfer of LO phase noise to the wanted frequency band. The input referred noise power due to the loop is expressed by (9) where denotes the input referred thermal noise power contribution of the filter core, the input blocker power level, the active feedback interference cancellation loop selectivity in dB at offset frequency from the wanted signal, Especially at high input blocker levels and thus high blocker replica levels at the active filter core output local oscillator phase noise can dominate the inband noise in the wanted channel. The situation is further aggravated for blockers close to the wanted channel as the oscillator phase noise is large close to the carrier.…”

“…Cascode devices are used to form a low impedance node at the transconductor output to facilitate feedback signal summation in the current domain. An additional Q-enhancement circuit is used to increase the LC tank quality factor [9].…”

System design considerations for SAW-less front-ends at the example of GSM DCS1800

“…Q-enhanced LC tanks excel due to their relative simplicity of circuit implementation but suffer from high noise levels even in the absence of interferers (typically between 5 dB and 7 dB [2], [3]) and poor linearity. Therefore, this work focusses on an alternative method.…”

“…Therefore, efforts have been made to integrate the band select filter on chip by different methods. To this extent, quality factor enhanced LC bandpass circuits [2], [3] and active interference cancellation techniques have been investigated [4], [5].…”