---
title: "Selection criteria for ADC"
subject: "Instrumentation II"
chapter: 4
key: "semester_5/instrumentation_ii:adc-selection-criteria"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/adc-selection-criteria
site: BCT Engineering
---

# Selection criteria for ADC

Instrumentation II · Chapter 4: Interfacing A/D And D/A Converters

- Asked in: 2072 Kartik, 2 marks; 2068 Baisakh (old course), 4 marks; 2073 Shrawan, 2 marks (asked 3 times)
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/adc-selection-criteria
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-4

## Question

What are the selection criteria for A/D or D/A converter?

## Short answer

Criteria include resolution (bits), accuracy (INL, DNL), conversion rate/settling time, input full‑scale range, architecture (flash, SAR, sigma‑delta), interface (parallel/SPI/I²C), number of channels, power consumption, temperature stability, and cost.

## Answer

Selection of an A/D or D/A converter depends on the requirements of the application. The main criteria are:

1. **Resolution:** number of bits (8, 10, 12, 16). It decides the smallest detectable change (LSB = FSR / 2^n). For example, 12 bits over 10 V gives 2.44 mV.
2. **Accuracy:** total error from offset, gain, INL and DNL; should be better than +/-1/2 LSB.
3. **Conversion (sampling) speed:** conversion time for ADC, settling time for DAC. Needed sampling rate must exceed twice the highest signal frequency (Nyquist). Flash ADC is fastest, SAR is medium, dual slope is slow but accurate.
4. **Type/architecture:** flash, SAR, dual slope, sigma-delta for ADC; weighted resistor, R-2R, current steering for DAC.
5. **Input/output range:** unipolar or bipolar, voltage or current, reference voltage (internal or external).
6. **Linearity and monotonicity:** DNL, INL specified; no missing codes.
7. **Interface:** parallel or serial (SPI/I2C), compatibility with microprocessor bus and logic levels (TTL/CMOS), tri-state outputs, built-in latches.
8. **Number of channels:** with or without multiplexer and sample and hold.
9. **Power supply and consumption,** temperature range and stability (drift).
10. **Cost, package and availability.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. LSB of 12-bit over 10 V?
   A. 10 mV
   B. 2.44 mV
   C. 0.24 mV
   D. 4.88 mV
   Answer: B. 10/4096 = 2.44 mV. (Key point: Resolution)

2. Which ADC is fastest?
   A. Flash
   B. SAR
   C. Dual slope
   D. Sigma-delta
   Answer: A. Flash is fastest, dual slope slow but accurate. (Key point: Speed)

3. Sampling rate must exceed?
   A. 10 Hz
   B. Equal
   C. Half
   D. Twice the highest signal frequency
   Answer: D. Nyquist. (Key point: Sampling)

4. Accuracy should be better than?
   A. +/-5 LSB
   B. 10%
   C. +/-1/2 LSB
   D. 1 V
   Answer: C. Total error ideally within half LSB. (Key point: Accuracy)

## Related in Instrumentation II

- [ADC at 80H with 8255A: display on port B LEDs](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aadc-8255-80h-leds) — Instrumentation II, chapter 2
- [Good programming practice and software selection](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Agood-programming-software-selection) — Instrumentation II, chapter 9, asked 2×

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