Multi-carrier transceiver and multi-frequency pll system

Abstract

A multi-carrier transceiver receives and transmits wireless communication signals on multiple carriers simultaneously. To generate Local Oscillator (LO) signals for mixers operating at different frequencies, a multi-frequency LO signal generating circuit includes a set of integer-N Phase Locked Loop (PLL) circuits. All PLL circuits receive the same reference frequency, but output different frequency LO signals, each at an integer multiple of the reference frequency. The LO signal frequencies are thus on an equidistant frequency grid having a granularity of the reference frequency. Spurs are also at multiples of the reference frequency, and can be easily filtered. A fractional-N PLL circuit may generate the reference frequency, making the frequency grid adjustable. A plurality of the PLL circuits in the set output a phase error feedback signal to a phase error correction circuit, and receive a phase error control signal that phase-locks the plurality of PLL circuits together and mitigates phase noise deviations between them. PLL circuits operating near a transmitter frequency are not in the phase-locked plurality, so all PLL circuits are not frequency pulled. Complex channel select filters are used for carriers not aligned with a LO signal.