MT-022

∑

1-BIT

DAC

+

–

∑

N-BIT

DAC

∫

+

–

N-BIT

FLASH

ADC

ANALOG

INPUT

ANALOG

INPUT

DIGITAL

OUTPUT

DIGITAL

OUTPUT

(A) DELTA MODULATION

(B) DIFFERENTIAL PCM

SAMPLING CLOCK

∫

SAMPLING CLOCK

Figure 1: Delta Modulation and Differential PCM

If the analog signal remains at a fixed dc level for a period of time, an alternating pattern of "0s"

and "1s" is obtained. It should be noted that differential PCM (see Figure 1B) uses exactly the

same concept except a multibit ADC is used rather than a single comparator to derive the

transmitted information.

Since there is no limit to the number of pulses of the same sign that may occur, delta modulation

systems are capable of tracking signals of any amplitude. In theory, there is no peak clipping.

However, the theoretical limitation of delta modulation is that the analog signal must not change

too rapidly. The problem of slope clipping is shown in Figure 2. Here, although each sampling

instant indicates a positive excursion, the analog signal is rising too quickly, and the quantizer is

unable to keep pace.

SLOPE OVERLOAD

Figure 2: Quantization Using Delta Modulation

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