Discuss the working of ADCs and DACs with suitable block diagrams. Mention their applications in DAQ systems.

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Accepted Answer

## ADC and DAC

### ADC (Analog-to-Digital Converter)
Converts a continuous analog voltage into an n-bit digital code. Resolution: $\Delta = V_{ref}/2^n$.

```mermaid
flowchart LR
  A[Analog input] --> B[Sample and hold]
  B --> C[Quantizer]
  C --> D[Encoder]
  D --> E[n-bit digital output]
```

**SAR ADC working:** a successive approximation register sets bits from MSB to LSB; an internal DAC output is compared with the input; the comparator keeps or clears each bit. Result is ready after n clock cycles.

```mermaid
flowchart LR
  VIN[Vin] --> CMP[Comparator]
  DAC[Internal DAC] --> CMP
  CMP --> SAR[SAR logic]
  SAR --> DAC
  SAR --> OUT[Digital output]
```

| ADC type | Speed | Resolution | Use |
|---|---|---|---|
| Flash | Fastest | Low | Video, oscilloscopes |
| SAR | Medium | 8 to 18 bit | General DAQ |
| Dual-slope | Slow | High | Digital multimeters |
| Sigma-delta | Slow to medium | Very high | Biomedical, audio |

### DAC (Digital-to-Analog Converter)
Converts a digital code into an analog voltage: $V_{out} = V_{ref} \cdot D/2^n$.

```mermaid
flowchart LR
  A[Digital code] --> B[Resistor network R-2R]
  B --> C[Summing op-amp]
  C --> D[Analog output]
  R[Vref] --> B
```

The R-2R ladder is common because it needs only two resistor values and is accurate.

### Applications in DAQ
- ADC: digitizes sensor signals such as ECG, temperature and pressure.
- DAC: produces control signals, test stimulus, waveform generation, actuator drive and calibration.

### Exam tip
Give the formula for resolution, draw the SAR block diagram and the R-2R DAC.

ADC and DAC

ADC (Analog-to-Digital Converter)

DAC (Digital-to-Analog Converter)

Applications in DAQ

Exam tip

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