Digital Technique for Instability Detection and Saturation Recovery in High-Order SC Sigma-Delta Modulators

Stability and saturation recovery are a key concern in High-order Switched Capacitor (SC) SigmaDelta modulators, since they are conditionally stable architectures. A novel digital technique, which allows to detect instability in the digital domain, a fast recover of high-order modulators from instability and guarantees a minimum of Signal-to-Noise Ratio (SNR) also when the architecture gets unstable, is proposed. This technique operates in two steps: first, the instability is detected in the digital domain and the system is recovered to a proper operation and then a digital post-processing is performed in order to achieve a residual SNR also in the instability condition. This strategy has been applied to a 6th-order SC bandpass SigmaDelta modulator operating at 42.8 MHz and featuring 74 dB Dynamic Range (DR) in a 200 kHz bandwidth. The benchmark modulator has been integrated in a standard double-poly 0.35 mum 3.3 V CMOS technology with five metal layers