The LM1881 is a video sync separator IC designed to extract timing signals from an analog composite video input. A composite video signal carries picture information, horizontal sync, vertical sync, blanking periods, and color timing in one waveform. The LM1881 separates these timing parts and provides useful outputs such as composite sync, vertical sync, odd/even field detection, and burst or back-porch timing.

Catalog

LM1881 Pinout Details

What Does the LM1881 Do?

Separates Sync Signals from Composite Video

The LM1881 receives a composite video signal that contains picture information and synchronization pulses. It removes most of the video content and extracts the timing signals needed by displays, video processors, and control circuits.

Produces a Composite Sync Output

The composite sync output combines the horizontal and vertical synchronization information into one timing signal. This output can be used to synchronize video equipment, trigger measurement instruments, or control circuits that must follow the video scan timing.

Extracts the Vertical Sync Signal

The LM1881 provides a separate vertical sync output that indicates the start of each video field. This signal is useful for frame timing, video switching, image capture, and circuits that need to detect when a new field begins.

Identifies Odd and Even Video Fields

For interlaced video signals, the odd/even output indicates whether the current field is odd or even. This helps video-processing systems correctly combine two fields into a complete frame.

Generates a Burst and Back-Porch Timing Pulse

The burst/back-porch output produces a timing pulse during the back-porch portion of the video signal. It can be used for DC restoration, clamping, color-burst timing, and other analog video-processing functions.

Supports Different Video Timing Standards

The LM1881 can work with several standard composite and vertical synchronization formats. Its internal timing can be adjusted with an external resistor connected to the RSET pin, allowing the circuit to accommodate different video timing conditions.

Simplifies Video Synchronization Circuits

Without the LM1881, separating synchronization pulses would require several comparators, filters, timing components, and logic circuits. The IC combines these functions in one compact package, reducing circuit complexity and component count.

LM1881 Key Specifications

How Does the LM1881 Work?

The LM1881 receives a composite video signal through pin 2 and detects the synchronization pulses inside it. Internal comparators separate the sync information from the picture content, allowing the IC to generate a clean composite sync output at pin 1.

The IC also analyzes the timing of the sync pulses to detect the vertical synchronization interval. It then provides a separate vertical sync signal at pin 3 and identifies odd and even fields through pin 7 when working with interlaced video.

Pin 5 produces a burst gate or back-porch timing pulse, which is useful for video clamping and color-processing circuits. The external resistor connected to pin 6 sets the internal timing current. In this way, the LM1881 converts one composite video input into several useful timing signals for video-processing equipment.

LM1881 Typical Application Circuit

Video Line Selector Circuit

In this video line selector circuit, the LM1881 receives the composite video signal through the input coupling network. It separates the synchronization information from the picture signal and produces timing pulses used by the logic section. The 680 kΩ resistor and nearby capacitors set and stabilize the LM1881 timing.

The extracted sync signals control the MM74C00 logic gates and MM74C193 counters. These components count the video lines and generate selection signals for different line ranges. The line-select switches allow the circuit to choose which part of the video frame will pass to the output.

The CD4066 analog switch then connects the selected section of the video signal to the video line output. To use this circuit, apply a standard composite video signal at the input, power the circuit from 5 V, and set the line-select switches for the required line range. The LM1881 provides the timing reference, while the counters and logic determine when the video signal is allowed through.

Multiple Video Line Selector Circuit

In this multiple video line selector circuit, the LM1881 receives the composite video signal and separates its synchronization pulses from the picture information. The extracted sync signal provides the timing reference needed to identify each video line accurately.

The MM74C193 counters count the incoming lines, while the MM74C00 logic gates compare the count with the settings selected by the switches. This allows the circuit to choose a group of consecutive video lines instead of only one line.

The CD4066 analog switch passes the selected video section to the output. The added black-level restoration network keeps the output reference level stable after switching. To use the circuit, apply a composite video signal, power it from 5 V, and set the switches for the starting line and number of continuous lines required.

How to Select the LM1881 RSET Resistor

• Connect the RSET resistor between pin 6 and ground. It controls the LM1881 internal timing current.

• Use 680 kΩ for standard NTSC, PAL, and similar composite video signals. This is the typical recommended value for common video line rates.

• Choose a larger resistor when a longer internal timing delay is required. However, a value that is too high can make vertical sync detection less reliable.

• Choose a smaller resistor when a shorter timing delay is needed. A value that is too low may cause incorrect or multiple vertical sync pulses.

• For non-standard video formats, select RSET according to the horizontal line frequency and vertical sync timing shown in the datasheet graphs.

• Keep the resistor value below about 2 MΩ, because leakage current and circuit noise can reduce timing accuracy at very high resistance values.

• After selecting the resistor, check pin 3 with an oscilloscope. The vertical sync output should produce one stable pulse for each video field.

• Keep the pin 6 connection short and away from noisy output traces to reduce parasitic capacitance and interference.

Practical LM1881 Applications

Video Monitor Synchronization

The LM1881 can extract composite and vertical sync signals from an analog video source. These outputs help monitors and display circuits maintain stable horizontal and vertical timing.

Video Capture Systems

Video capture equipment can use the vertical sync output to identify the start of each field. This helps the system sample, store, or process incoming video at the correct time.

Video Switching Circuits

In multi-camera and video-routing systems, the LM1881 provides timing signals for controlled source switching. Proper synchronization can reduce picture rolling, tearing, and unstable transitions.

Frame and Field Detection

The vertical sync and odd/even outputs allow a circuit to detect individual fields in interlaced video. This is useful for frame counters, field-based processing, and video timing control.

On-Screen Display Circuits

Text and graphics overlay circuits need accurate sync timing to place information at the correct screen position. The LM1881 supplies the timing references required for stable on-screen displays.

Video Clamp Circuits

The burst or back-porch output can control a clamping circuit during the blanking interval. This helps restore a stable DC reference level before further video amplification or processing.

Test and Measurement Equipment

Oscilloscopes, video testers, and diagnostic instruments can use the LM1881 outputs as trigger signals. This makes it easier to examine specific lines, fields, or sections of a video waveform.

Legacy Video Equipment

The LM1881 is commonly used in equipment that works with composite analog video, including older cameras, game consoles, CCTV systems, video recorders, and broadcast devices.

LM1881 vs EL1881 vs LMH1980

LM1881 Alternatives and Replacements

• EL1881

• EL1883

• LMH1980

• LMH1981

• LMH1982, etc.

LM1881 Mechanical Dimensions

Packaging Information

How to Choose a Video Sync Separator IC

Choose a video sync separator IC based on the video format, supply voltage, required outputs, and circuit compatibility. For standard NTSC, PAL, or SECAM composite video, the LM1881 or EL1881 is usually sufficient. For HD, component video, tri-level sync, or automatic format detection, a device such as the LMH1980 is more suitable.

Also check the required outputs before selecting a part. Some circuits only need composite and vertical sync, while others require horizontal sync, odd/even field detection, or back-porch timing. Confirm the package, operating temperature, power consumption, and whether the new IC is pin-compatible with the existing PCB.