In the conventional form of DM, the quantizer input may be viewed as an approximate to the derivative of the incoming message signal m(t). This behavior leads to a drawback of DM: transmission disturbances (e.g., noise) result in an accumulation error in the demodulated signal. This drawback can be overcome by integrating the message signal m(t) prior to DM, resulting in three beneficial effects:

a. Low frequency content of m(t) is pre-emphasized.

b. Correlation between adjacent samples of m(t) is increased, tending to improve overall system performance by reducing the variance of the error signal at the quantizer input.

c. Design of the receiver is simplified. Such a DM scheme is called delta-sigma modulation. Construct a block diagram of the delta-sigma modulation system in such a way that it provides an interpretation of the system as a "smoothed" version of 1-bit PCM in the following composite sense:

• smoothness implies that the comparator output is integrated prior to quantization, and

• 1-bit modulation merely restates that the quantizer consists of a hard limiter with only two representation levels. Explain how the receiver of the delta-sigma modulation system is simplified, compared with conventional DM.