DSP Implementation of Adaptive Notch Filters With Overflow Avoidance in Fixed-Point Arithmetic

In this paper, we implement adaptive notch filters with constrained poles and zeros (CPZ-ANFs) using fixed-point DSP. Since the CPZ-ANFs are IIR filters that have narrow notch width, a signal can be amplified significantly in their feedback loops. Therefore, direct-form II structure suffers from high probability of overflow in its internal state. When an overflow occurs in internal state of filters, inaccurate values due to the overflow are used repeatedly to calculate the output signal of the filters. As a result, the filters do not operate correctly and therefore we have to prevent such overflow. In order to avoid the overflow, we use direct-form I structure in implementation of the CPZ-ANFs. Experimental results show that our method allows the CPZ-ANFs to operate properly on the fixed-point DSP.