*Question E4A01:
Which of the following limits the highest frequency signal that can be accurately displayed on a digital oscilloscope?*  

*Correct Answer is  A: Sampling rate of the analog-to-digital converter*  

### AI Response: (may contain errors)  

To determine the highest frequency signal that can be accurately displayed on a digital oscilloscope, we need to consider the sampling rate of the analog-to-digital converter (ADC).

### Explanation:

1. **Correct Answer: Sampling rate of the analog-to-digital converter (Choice A)**

   - The **Nyquist Theorem** states that to accurately sample a signal, the sampling rate must be at least twice the highest frequency component of the signal. This is known as the **Nyquist rate**.
   - If the sampling rate is less than twice the signal frequency, **aliasing** occurs, leading to inaccurate representation of the signal.
   - Therefore, the sampling rate of the ADC is the primary factor that limits the highest frequency signal that can be accurately displayed.

2. **Why the other choices are incorrect:**

   - **Analog-to-digital converter reference frequency (Choice B):** 
     - This refers to the internal clock frequency used by the ADC for its operation, but it does not directly determine the maximum frequency that can be sampled. The sampling rate is the critical factor.
   
   - **Q of the circuit (Choice C):**
     - The Q factor, or quality factor, relates to the bandwidth and selectivity of a circuit, not the sampling capability of an oscilloscope. It does not affect the maximum frequency that can be displayed.
   
   - **All these choices are correct (Choice D):**
     - Since only the sampling rate directly affects the maximum frequency that can be accurately displayed, this choice is incorrect.

### Useful Formula:

- **Nyquist Rate:**  
  $$ f_s \geq 2 \times f_{\text{max}} $$
  where:
  - $f_s$ = sampling rate
  - $f_{\text{max}}$ = highest frequency of the signal

This formula helps ensure that the signal is sampled adequately to avoid aliasing and accurately display the waveform on a digital oscilloscope.