*Question E4A05:
What is the purpose of using a prescaler with a frequency counter?*  

*Correct Answer is  D: Reduce the signal frequency to within the counter's operating range*  

### AI Response: (may contain errors)  

A prescaler is a device used in conjunction with a frequency counter to extend the range of frequencies that the counter can measure. Here's a breakdown of why the correct answer is correct and why the other choices are incorrect:

### Correct Answer: D

**Reduce the signal frequency to within the counter's operating range**

- **Explanation**: A prescaler divides the input frequency by a fixed integer value, effectively reducing the frequency to a level that the frequency counter can handle. This allows the counter to measure frequencies higher than its normal operating range. For example, if a prescaler divides the frequency by 10, a 1 GHz signal would be reduced to 100 MHz, which is easier for the counter to process.

### Incorrect Choices:

**A: Amplify low-level signals for more accurate counting**

- **Explanation**: A prescaler does not amplify signals. Its function is to divide the frequency, not to increase signal amplitude. Amplification is typically handled by a separate amplifier circuit.

**B: Multiply a higher frequency signal so a low-frequency counter can display the operating frequency**

- **Explanation**: A prescaler divides the frequency, not multiplies it. Multiplying the frequency would make it even higher, which is the opposite of what is needed for a counter with a limited frequency range.

**C: Prevent oscillation in a low-frequency counter circuit**

- **Explanation**: Preventing oscillation is not a function of a prescaler. Oscillation issues are usually addressed through circuit design and stabilization techniques, not by using a prescaler.

### Useful Formula:

If the prescaler divides the frequency by a factor of $N$, the relationship between the input frequency ($f_{\text{in}}$) and the output frequency ($f_{\text{out}}$) is:

$$f_{\text{out}} = \frac{f_{\text{in}}}{N}$$

This formula shows how the prescaler reduces the input frequency to a level that the frequency counter can measure.