Takeshi Imaike

Noise in high-speed digital-to-analog converters

We report on the measurement of phase noise of high speed analog to digital converters in a full digital measurement setup and for various development boards. The tested configurations ensures a Nyquist rate higher than 100 MHz suitable for conventional ultralow noise devices. Several analog to digital converters featuring a SNR higher than 140 dB enable the measurement of AM and PM noise with a background noise of -185 dBc (floor) and -160 dBc (flicker, 10 Hz off the carrier) using cross-correlation technique.

A new method to increase loaded Q of extremely low phase noise SAW oscillator

We have previously proposed a circuit configuration of SAW oscillator for extremely low phase noise, the name of which is Fr oscillator. The Fr oscillator has been able to realize extremely low phase noise floor level in calculation; however, the loaded Q is lower than Colpitts type oscillator. Then we propose new method to increase loaded Q. Using this method, we show several characteristics of the loaded Q. Based on the results, we estimate SSB phase noise of the Fr oscillator. As a result, the phase noise level is improved about 15 dB in the neighborhood of carrier frequency if the input/output impedance of the frequency selective circuit is reduced. Furthermore, we make a couple of Fr oscillators using crystal resonator. The measured phase noise characteristics are corresponding to the calculated value well. It is clear that this method is effective for improving phase noise of near the carrier frequency.