Effects of Oscillator Phase Noise on Frequency Delta Sigma Modulators with a High Oversampling Ratio for Sensor Applications

Abstract

Frequency delta sigma modulation (FDSM) is a unique analog to digital conversion technique featuring large dynamic range with wide frequency band width. It can be used for high performance digitaloutput sensors, if the oscillator in the FDSM is replaced by a variable frequency oscillator whose frequency depends on a certain external physical quantity. One of the most important parameters governing the performance of these sensors is a phase noise of the oscillator. The phase noise is an essential error source in the FDSM, and it is quite important for this type of sensors because they use a high frequency oscillator and an extremely large oversampling ratio. In this paper, we will discuss the quantitative effects of the phase noise on the FDSM output on the basis of a simple model. The model was validated with experiments for three types of oscillators.

Experimental Demonstration of a Hard-Type Oscillator Using a Resonant Tunneling Diode and Its Comparison with a Soft-Type Oscillator

“…Regarding the stability of the oscillators, one of the most important properties is a phase noise [26]- [28], which governs the performance of the communication systems, sensors [29]- [31], etc., using the oscillators. Figure 4 shows the oscillation frequency and the phase noise at the offset frequency of 100 kHz as a function of the bias voltage.…”

A Novel Displacement Sensor Based on a Frequency Delta-Sigma Modulator and its Application to a Stylus Surface Profiler

“…This implementation is promising because the Q-factor of the resonator is much larger than the LC oscillator using a condenser microphone and an inductor [10]. This large Q-factor results in low phase noise oscillation, which is essential to obtain wide dynamic range [15]. This microphone can be regarded as a displacement sensor for the diaphragm.…”