A 250MHz 11Bit 20mW CMOS Low-Hold-Pedestal Fully Differential Track-and-Hold Circuit

A new technique for realizing a very-high-speed low-power low-voltage fully differential CMOS track-and-hold circuit with low hold pedestal is presented. To achieve high sampling linearity the circuit utilizes bootstrapped input switch. The fully differential design relaxes the trade-off between sampling speed and the sampling precision. The circuit design of major building blocks is described in detailed. A prototype circuit in a 0.35-mum CMOS process is integrated and experimental results are presented. The track-and-hold circuit operates up to 250MHz of sampling frequency with less than -69dB of total harmonic distortion corresponding to 11bits for an input 85MHz sinusoidal amplitude of 1.8 V_pp at a 3V supply. This total harmonic distortion measurement reflects the held values as well as the tracking components of the output waveform. In these conditions, a differential hold pedestal of less than 1mV, 0.8ns acquisition time at 1.8V step input, and 1.8 V_pp full-scale differential input range are achieved. The circuit dissipates 20mW with a 3V power supply