Which of the following statements is/are correct?
S1: Filter controls the lock range of the PLL.
S2: Filter controls the capture range of the PLL.

Explanation:

Phase-Locked Loop (PLL) Filters

Definition: A Phase-Locked Loop (PLL) is an electronic circuit that controls an oscillator so that it maintains a constant phase angle relative to a reference signal. The PLL filter plays a crucial role in determining the performance characteristics of the PLL, specifically its lock range and capture range.

Lock Range: The lock range of a PLL is the range of frequencies over which the PLL can maintain lock with the input signal once it has initially locked. This means that if the input signal frequency drifts within this range, the PLL can still follow and maintain synchronization.

Capture Range: The capture range, on the other hand, is the range of frequencies over which the PLL can initially acquire lock with the input signal. If the input signal frequency is within this range, the PLL can adjust itself to lock onto the signal.

PLL Filter's Role:

• **Lock Range Control:** The lock range is primarily influenced by the VCO (Voltage-Controlled Oscillator) and the overall loop gain of the PLL. The filter has a minimal direct effect on the lock range.
• **Capture Range Control:** The capture range is significantly affected by the characteristics of the PLL filter. The filter's bandwidth and damping factor play crucial roles in determining how quickly the PLL can lock onto a new input frequency and how wide the capture range will be.

Correct Statement Analysis:

Given the two statements:

• S1: Filter controls the lock range of the PLL.
• S2: Filter controls the capture range of the PLL.

Analyzing these statements:

• S1: This statement is incorrect. The filter does not control the lock range of the PLL. The lock range is more influenced by the VCO and the loop gain.
• S2: This statement is correct. The filter indeed controls the capture range of the PLL, as the filter characteristics directly impact the ability of the PLL to acquire lock within a certain frequency range.

Therefore, the correct option is Option 4: Only S2.

Important Information:

Additional Insights on Other Options:

• Option 1: Both S1 and S2 cannot be correct because S1 is incorrect.
• Option 2: Neither S1 nor S2 cannot be correct because S2 is correct.
• Option 3: Only S1 cannot be correct because S1 is incorrect.

Summary:

The PLL filter plays a pivotal role in determining the capture range of the PLL, influencing how quickly and effectively the PLL can lock onto a new input frequency. However, the lock range is predominantly governed by the VCO and loop gain, making the filter's impact on the lock range minimal. This distinction is critical in understanding the correct statement regarding PLL filter functions.