Stability Analysis of Oscillators Based on a Delta-Sigma Topology

The growing demand of mixed-signal integrated circuits encourages the research of Built- In Self-Test (BIST) techniques to achieve simpler and less expensive testing processes. High quality sinusoidal oscillators based on a Δ-Σ topology are an effective solution to perform the test of this kind of devices. Unfortunately, due to the in-loop 1-bit quantizer nonlinearity, several problems of stability have been observed. A stability analysis on the behavior of the oscillator based on a second order Δ-Σ modulator presented in [1] is described in this paper. In particular, it is shown that the oscillator is intrinsically unstable and its complete dynamics is very difficult to predict exactly. Finally, a possible stabilization strategy is proposed.