Comments on "Bandpass Sigma-Delta Modulator Employing SAW Resonator as Loop Filter

Some corrections needed in the theoretical analysis of the surface acoustic wave resonator loop filter for a bandpass sigma-delta modulator, as presented by Yu and Xu, are pointed out. A simple idea is also proposed for perfect cancellation of anti-resonance without substantially affecting the resonance frequency, but with the added benefits of an enhanced factor and insertion gain, rather than insertion loss. However, a practical implementation of the idea remains an open question.