Behavior of a 1-bit 2nd-order ΔΣ-modulator under wideband excitation

The internal signal swings of a 1-bit 2^nd-order ΔΣ-modulator were found in simulations to increase uncontrollably as the frequency of a sinusoidal excitation exceeded a certain boundary. This is highly undesirable in radio receivers utilizing digital channel selection as the unfiltered input will contain strong high frequency components. The simulated behavior is confirmed by experimental results from an integrated prototype which suffers from a rapid loss of SNR above the same boundary frequency. The frequency dependent behavior is explained by the correlation between the input signal and the impulse response of the 1-bit ΔΣ-modulator´s loop filter. Simulations indicate that reducing the gain coefficient of the first integrator or alternatively employing multibit quantization eliminates the problem