AD/DA conversion

What is the effect of raising the order of the modulator in a ΔΣ AD converter (for example, from first to second order)?

  1. AThe sampling frequency can be lowered
  2. BQuantization noise is pushed more strongly to high frequencies, reducing in-band noise at the same oversampling ratio
  3. CThe decimation filter becomes unnecessary
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Answer: B. Quantization noise is pushed more strongly to high frequencies, reducing in-band noise at the same oversampling ratio

A ΔΣ modulator pushes quantization noise to higher frequencies (noise shaping), and a higher order suppresses the low-frequency noise more strongly. The in-band SNR therefore improves at the same oversampling ratio. However, higher-order modulators tend to become unstable and need careful design.

  • A. Lowering the sampling frequency is not the direct effect of raising the order.
  • B. Correct. Noise shaping becomes stronger and in-band noise decreases.
  • C. A decimation filter is still needed to remove the high-frequency noise.
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More AD/DA conversion questions

  1. In a time-interleaved ADC that alternates between several ADCs, what problem is caused by mismatches in offset, gain and timing between the individual ADCs?
  2. Which correctly describes the "offset binary" code used in ADCs that handle both positive and negative voltages?
  3. How many output levels can an 8-bit AD converter represent?
  4. What sampling frequency is needed to sample an analog signal containing components up to 20 kHz without aliasing?
  5. Which is a characteristic of a flash AD converter?