RF Phase Trimmer: Basics and Types

This page explains the basics of RF phase trimmers and illustrates an RF phase trimmer circuit used to shift the phase of an RF signal. We’ll cover different RF phase trimmer types, including fixed, variable, analog, and digital trimmers.

Definition:

An RF phase trimmer is a device designed to change the phase of an input RF signal to a desired phase at the output. Crucially, it achieves this phase shift while introducing minimal attenuation to the input signal. The range of phase adjustment is frequency-dependent.

Function:

RF phase trimmers are used for phase matching between two systems or even between two cables where precise phase alignment is critical. They find application in:

• High-speed digital lines
• High-frequency communications
• Broadband applications

Based on the adjustment capabilities, RF phase trimmers are classified as follows:

• Fixed: Provides a fixed, predetermined amount of phase shift between the input and output ports.
• Variable: Allows for a variable change in the phase shift between the input and output.

RF Phase Trimmer Types: Analog and Digital

Depending on the components used in their construction, RF phase trimmers are further categorized into analog and digital types.

Analog RF Phase Trimmer

Figure 1 depicts a typical analog RF phase trimmer. As shown, it is constructed using resistors (R) and capacitors (C). A single RC network can provide a 45-degree phase shift between the input and output. By cascading such networks, a desired overall phase shift can be achieved. These analog phase trimmers are generally available for frequencies up to 18 GHz.

Digital RF Phase Trimmer

Digital phase trimmers are typically designed using PIN diodes. They leverage digital control signals to route the input RF signal through different electrical lengths. This allows for discrete phase