Low‐frequency noise analysis and minimization in Gilbert‐cell‐based mixers for direct‐conversion (zero‐IF) low‐power front‐ends

Low‐frequency (flicker) noise is one of the most important issues in the design of direct‐conversion zero‐IF front‐ends. Within the front‐end building blocks, the direct‐conversion mixer is critical in terms of flicker noise, since it performs the signal down‐conversion to baseband. This paper analyzes the main sources of low‐frequency noise in Gilbert‐cell‐based direct‐conversion mixers, and several issues for minimizing the flicker noise while keeping a good mixer performance in terms of gain, noise figure and power consumption are introduced in a quantitative manner. In order to verify these issues, a CMOS Gilbert‐cell‐based zero‐IF mixer has been fabricated and measured. A flicker noise as low as 10.4 dB is achieved (NF at 10 kHz) with a power consumption of only 2 mA from a 2.7 V power supply. More than 14.6 dB conversion gain and noise figure lower than 9 dB (DSB) are obtained from DC to 2.5 GHz with an LO power of ?10 dBm, which makes this mixer suitable for a multi‐standard low‐power zero‐IF front‐end. Copyright © 2008 John Wiley & Sons, Ltd.