Simple quadrature oscillator for BIST∗

In this letter, a simple quadrature oscillator for built-in self-test (BIST) of integrated analog filters is proposed. A new hardware-efficient approach for amplitude control is described, with as main assets: (i) the technique requires little hardware which makes it very useful for BIST, (ii) the oscillation amplitude is well defined, and (iii) the distortion-level introduced by the amplitude control loop is under control of the designer. Introduction Quadrature oscillators are used in a number of diverse applications. In telecommunication systems they are key building blocks in many (de)modulation schemes. However, quadrature oscillators are also useful in instrumentation and measurement systems, e.g., measuring an unknown impedance as a function of frequency [1]. The focus of this letter is on another instrumentation-related application: built-in self-test (BIST) of integrated analog filters. Here, the in-fase signal vI of the quadrature oscillator is applied to the analog filter to be tested (fig. 1). The output voltage of the filter is then demodulated by means of the quadrature signals for extracting amplitude and fase information of the analog filter transfer. In general, it is expected that the importance of such built-in self-test feature will steadily grow to guarantee proper operation of performance-critical analog blocks.