Recent Advances in High-Performance Frequency Synthesizer Design

Whether employed as local oscillators in wireless communications or radar systems, or as clock generators in data converters, high-performance frequency synthesizers are essential elements of any advanced electronic systems. In wireless applications, highly spectral-efficient modulations, such as quadrature amplitude modulation with large number of symbols (256 or above), enables higher bit rate at same bandwidth occupation, at the price of tighter constraints on the error-vector magnitude. This demands for an ultra-low jitter local oscillator (LO). For instance, the 5G new radio for cellular communications at frequencies around 28GHz calls for an integrated phase noise well below -36dBc, translating into an absolute rms jitter well below 90fs, over all the operating conditions. Similar performance is also required to the clock of high-speed analog-to-digital converters not to deteriorate their signal-to-noise ratio (SNR). An SNR of 62dB (i.e., 10 equivalent bits) at 1GHz bandwidth requires a clock jitter well below 130fs.