Phase Locked Loop Basics — Lesson 1

This lesson covers the eleventh basics of phase-locked loop. The lesson explains the need for pure, agile, and accurate frequencies, and how quartz crystals and voltage-controlled accelerators can meet these requirements. It also discusses the concept of phase noise and the importance of a control system that tracks the phase of the reference oscillator. The lesson further delves into the properties of control systems, the concept of velocity control systems, and the role of phase detectors in these systems. It also provides a detailed explanation of how a phase-locked loop works and how to build a control system.

Video Highlights

05:22 - Phased locked loop
12:17 - Need for a velocity control system
19:21 - Partial fraction breakup
32:19 - Phase detector and its role in comparing the phase of the reference oscillator with the phase of the VCO
48:01 - State machine diagram and the importance of having two binary digits to represent the output

Key Takeaways

- Quartz crystals are excellent for achieving pure and accurate frequencies, while voltage-controlled accelerators are agile and can change frequencies.
- A control system that tracks the phase of the reference oscillator is crucial to reduce phase noise.
- The control system should mimic the reference phase and drive the voltage-controlled oscillator (VCO).
- The control system, known as a phase-locked loop, compares the reference phase with the phase of the VCO and controls the plant (VCO).
- The phase of the reference oscillator looks like a ramp, and the control system needs to be a velocity control system to track this continuously changing input.
- The output of a position control system is precisely equal to the input when the input is a step function. However, if the input is a ramp, the output will have a constant error.
- A phase detector is needed to compare the phase of the reference oscillator with the phase of the VCO.