Phase Detectors—A Brief Overview

July 5, 2019

Phase detectors are an integral part of modern day electronics and control systems. This article overviews the basic concepts of phase detectors.

What are phase detectors?

Phase detectors are circuits that generate a voltage signal proportional to the phase difference existing between two input signals.

What is phase?

Phase is the position of a point on a waveform at a given instant.

So, when we’re talking about phase difference,we’re referring to the difference in position of a wave point on corresponding signals measured at any given instance.

What are some common applications of phase detectors?

Phase detectors can be used in all those applications where detecting phase difference between two input signals forms a critical requirement. Some common application areas of phase detectors include:

• Servo mechanisms
• Radar systems
• Telecommunication systems
• Motor control
• Demodulators

Although, phase detectors can be implemented as standalone circuits in a system, they are usually applied as part of phase locked loops.

How many types of phase detectors are there?

There are mainly two types of phase detectors:

• Phase-only sensitive detectors
• Phase-frequency detectors

Let’s briefly discuss them one by one.

Phase-only sensitive detectors are the simplest type of phase detectors. They produce an output voltage based upon the phase difference that existsbetween the two input signals. When the phase difference is steady, they produce a constant output voltage. When the phase difference varies, they produce a varying output voltage. This latter condition, however, can sometimes put these detectors at an operational disadvantage. The variable frequency of the resulting output voltage may fall outside the PLL loop filter, rendering these detectors ineffective. There are two forms of phase-only sensitive detectors commonly used today; XOR phase detectors and double balanced mixer (DBM) phase detectors.

Phase frequency detectors are improved versions of phase-only sensitive detectors. Like phase-only sensitive detectors, they produce an output voltage proportional to the phase difference between the two input signals. However, unlike their counterparts, they don’t let a potential frequency difference affect their operation. There are two forms of phase sensitive detectors widely used today; dual D type phase comparators and edge triggered JK flip flop detectors.

That completes our overview of phase detectors; we hope you found the information useful.

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