International Business Machines Corporation

Prominent Communications, Inc.

Hung-Chuan Pai

Nicolas Sornin

Liang Dai

Kevin Hsi-Huai Wang

Laurent Claude Perraud

Gerald J Twomey

Jie Huang

Cheryl Jean Herdey

Shane Kaiser

An offset correction analogic circuit capable of compensating the offset of a digital baseband is described. The circuit comprises analog means to receive an output differential signal issued from a differential signal path. The differential signal path may be a baseband filter as used in digital communication systems. The baseband filter inputs an input differential signal having an offset to be compensated. The output differential signal is fed into an analog integrator to generate a pulsed signal either on a first output line or on a second output line according to the polarity of the output differential signal. The pulsed signal is then integrated into a switched capacitor and a differential compensation offset signal is issued. The frequency of the pulsed signal is preferably proportional to the voltage value of the output differential signal. The compensation offset signal may be summed with the input differential signal into a summing circuit.

Fully integrated offset compensation feedback circuit

The voltage-oscillator (VCO) in a frequency synthesizer using a phase-locked loop (PLL) is calibrated during power up or channel switching. The VCO has a coarse frequency control and a fine frequency control. The coarse control consists of digital bits that are used for calibration. The coarse control is connected to the charge pump output as in a regular PLL. By searching for the optimal control setting, the center frequency of the VCO is trimmed close to the desired frequency for the PLL to lock. This allows small VCO gain without losing the tolerance of process and temperature variations. As a result, the PLL phase noise performance is improved.

Fast VCO calibration for frequency synthesizers

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Hung-Chuan Pai