Image Credit: Colby Instruments | D & N Electronics | Digi-Key

Delay lines are devices used to slow down a signal by a time interval in an electrical network. There are two basic delay line technologies: passive and active. 

• Passive delay lines or analog delay lines (ADL) are built with analog components and can delay both analog and digital signals. They attenuate the signal from input to output and use components such as capacitors and inductors. 
• Active delay lines or digital delay lines (DDL) are built with digital components and are used to delay only digital signals. Active delay lines do not attenuate the signal from input to output, and are characterized by a specific logic family. Common logic families include transistor-transistor logic (TTL), complementary metal-oxide semiconductor (CMOS), and emitter-coupled logic (ECL).

Delay Line Specifications

Specifications for delay lines include delay line type, time delay, and rise time.

Rise time is the time required for the pulse amplitude from one specified level to another. Rise time, another important specification to consider, is the time required for the pulse amplitude from one specified level to another.

Time delay is the maximum delay in units of time that a delay line can provide.

Types of Delay Lines

There are two basic delay line types: fixed and variable.

• Fixed delay lines can delay signals by a time interval set by the manufacturer. For fixed delay lines, the delay time is the only delay time that can be set.
• Variable delay lines can delay signals between two values in a specified range. Generally, the low end of the range is zero. For variable delay lines, the delay time is the upper value of a tapped or programmable delay range.       

Package Types

There are several package types for delay lines.

• Surface mount technology (SMT) adds components to a printed circuit board (PCB) by soldering component leads or terminals to the top surface of the board.
• Through hole technology (THT) mounts components by inserting component leads through holes in the board and then soldering the leads in place on the opposite side of the board.
• Flat pack (FPAK) devices have flat leads and are available in a variety of body sizes and pin counts.

• Connectorized devices attach with coaxial or other types of connectors.

Delay Line Connectors

Delay lines use many types of radio frequency (RF) connectors.

• Bayonet Neil-Concelman (BNC) connectors are used in applications to 2 GHz.
• Threaded Neil-Concelman (TNC) connectors are similar in size to BNC connectors, but feature a threaded coupling nut for applications that require performance to 11 GHz.
• Miniature coaxial (MCX) connectors provide broadband capability through 6 GHz and are used in applications where weight and physical space are limited.
• Ultra high frequency (UHF) connectors are designed with non-constant impedance for use in comparatively low voltage and low frequency applications.
• Subminiature-A (SMA) connectors directly interface the cable dielectric without air gaps.
• Subminiature-B (SMB) connectors snap into place and are used for frequencies from DC to 4 GHz.

• Subminiature-P (SMP) connectors are rated to 40 GHz and, depending on detent type, can withstand from 100 to 100,000 interconnect cycles.

• Other connectors for RF attenuators include MMCX, Mini-UHF, Type F, Type N, 1.6/5.6, and 7-16 connectors. 

Standards

Delay Lines must adhere to several standards to ensure proper design and functionality.

• A-A-59465 - This CID covers the general requirements for active delay lines. Active delay lines covered by this CID are intended for commercial/industrial applications.
• DSCC-DWG-84035 - This drawing describes the requirements for a family of passive delay lines with 16 pins and 10 taps.
• MIL - D- 83532 - This specification covers the general requirements for fixed (tapped and untapped) pulse delay lines. The term Part or Identifying Number (PIN) is equivalent to the term (part number, identification number, and type designator) which was previously used in this specification. The PIN shall consist of the letter "M", the general specification number, the detail specification sheet number, a letter representing case style, an assigned dash number, a letter representing product assurance level, and a letter representing lead finish.