US Patent 7741926 Frequency synthesizer having improved frequency hopping

A frequency synthesizer switches the frequency at a high rate, is of low power consumption, and has a high signal-to-noise ratio. CMOS quadrature VCOs 31, 32 generate and output four-phase signals 36, 37, respectively. CMOS selector 33 selects either one of two four-phase signals 36, 37 generated by CMOS quadrature VCOs 31, 32 and outputs the selected signal as output signal 38. CMOS SSB mixer 34 multiplies output signal 38 selected by CMOS selector 33 and four-phase input signal 39 input from an external source by each other to generate a signal having a frequency represented by the sum of, or the difference between, the frequency of output signal 38 and the frequency of four-phase input signal 39, and outputs the generated signal as output signal 40. CML buffer 35 adjusts the level of output signal 40 from CMOS SSB mixer 34 and outputs the level-adjusted signal to another circuit.