Question E8A02:
Which of the following is a type of analog-to-digital conversion?  

Choices:  
A: Successive approximation  
B: Harmonic regeneration  
C: Level shifting  
D: Phase reversal    

Correct Answer is  A: Successive approximation  

Correct Answer: Successive approximation

1) Why it’s correct
- Successive Approximation is a standard analog-to-digital conversion (ADC) method. A SAR (Successive Approximation Register) ADC performs a binary search:
  - It compares the input voltage to a DAC-generated trial value, bit by bit from MSB to LSB.
  - After $N$ comparison steps, it yields an $N$-bit digital result.

2) Why the others are incorrect
- Harmonic regeneration: Refers to techniques using positive feedback or harmonic extraction (e.g., in regenerative or super-regenerative receivers). It’s not an A/D conversion method.
- Level shifting: An analog signal-conditioning operation that changes DC offset. It does not quantize or digitize the signal.
- Phase reversal: A 180° phase inversion (used in modulation like PSK). It is not an ADC technique.

3) Useful formulas and rules of thumb
- Quantization step (LSB size):  
  $$\Delta = \frac{V_{FS}}{2^N}$$
  where $V_{FS}$ is full-scale input range and $N$ is resolution in bits.
- Ideal quantization SNR:  
  $$\text{SNR}_{\text{quant}} \approx 6.02N + 1.76 \text{ dB}$$
- SAR conversion time (approximate):  
  $$t_{\text{conv}} \approx \frac{N}{f_{\text{clk}}}$$
  since a SAR typically needs one comparison per bit.
- Sampling rule (Nyquist):  
  $$f_s \ge 2 f_{\max}$$
  to avoid aliasing when digitizing analog signals.