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What is an A/D converter?

A/D Converter Configuration 4 (ΔΣ Type)


After oversampling of the analog signal is performed and converted into a series of pulses corresponding to the amplitudes of the analog signal through ΔΣ modulation, conversion into digital signals at the original sampling rate is completed by filtering data and removing out-of-band noise using a digital filter.


Quantization error is decreased by sampling at a higher frequency than the original sampling frequency.

Sampling frequency
Δ Σ Modulation

The difference (Δ) between the DAC output voltage and sampled voltage (via oversampling) is summed using an integrator. The sampled values are then converted into a series of pulses by comparing with a reference voltage using a comparator.
The output pulses are fed back to the input (which is delayed by one sampling operation), reducing the quantization error generated at the comparator in the low-frequency region. This requires modulation in order to become larger at higher frequencies.

ΔΣModulation Image

The pulse series output from the ΔΣ modulator often has a large quantization error component in the high-frequency region in addition to the original signal component. However, since these components are separated in frequency, it is easy to remove only the quantization error component using a digital filter and make it possible to achieve higher resolution compared with other methods.

  • Among the highest resolution of all A/D converters (up to 24bit)
  • Relatively slow conversion speed (200kHz max. sampling frequency)
  • Poor response makes it unsuitable for applications that connect a multiplexer to the input for switching between analog signal sources.
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