A harmonic quadrature LO generator using a 90° delay-locked loop [zero-IF transceiver applications]

To overcome problems with DC-offsets and LO pulling in zero-IF transceivers, a technique is presented to generate quadrature LO signals from an oscillator signal that is the N-th subharmonic of the desired RF frequency. A delay-locked loop is used to generate a set of LO signals that are spaced 90°/N apart. These can be applied directly to a harmonic mixer, or combined into quadrature LO signals for a standard mixer. A prototype implementation generates quadrature LO signals for a direct-conversion 5 GHz WLAN mixer from a half-frequency VCO in a 0.35 μm BiCMOS process. The current consumption is 9 mA and die area is 0.12 mm².