A Skew-Insensitive Switched Source-Follower Analog Frontend for Time-Interleaved ADCs

This paper presents a two-stage switched source-follower analog frontend (AFE) with high dynamic performance, by ingeniously combining the input-butter and the track-and-hold circuits. The proposed placement of the switches facilitates the circuit’s realization in advanced CMOS technologies, and it makes the circuit equally insensitive to any signal-dependent charge-injection. Moreover, a single nMOS switch can be efficiently shared among time-interleaved (TI) AFE channels in any traditional TIADC architecture. This way, the proposed two-stage AFE circuit becomes skew-insensitive. Operating at 2 GS/s, the AFE achieves a simulated peak spurious-free-dynamic-range (SFDR) of 76 dB for a 996 MHz input signal with a 700 m$\mathrm{V}_{\mathrm{P}\mathrm{P}}$ amplitude. Implemented in a 28 nm bulk CMOS process, it consumes 17 mA from a nominal analog 1.8 V power supply. Last but not the least, the proposed two-stage AFE circuit enables the combination of thick-gate and thin-gate devices avoiding any kind of reliability issues.