QVCO: Concepts and Classification

With the advent of CMOS technology, direct downconversion receivers are gaining popularity due to low cost and simplicity. Quadrature LO generation is critical to the operation of direct-downconversion receivers. Two common techniques for quadrature generation are divide-by-two frequency dividers, and polyphase filters. Divide-by-two dividers require the system’s oscillator to work at double the desired frequency, resulting in an overall increase in power consumption. Power consumption penalty is primarily due to the increase in power consumption of the VCO buffers. Polyphase filters allow quadrature generation without the need for doubling the frequency. The lossy nature of polyphase filters, however, results in increased power consumption (for buffering and amplifying signals).