Multi-Format Video Sync Separator # Technical Documentation: LMH1981MT Multi-Rate Video Clock Generator
Manufacturer : National Semiconductor (NS)
Component Type : Multi-Rate Video Clock Generator with Genlock
Package : TSSOP-14 (MT)
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## 1. Application Scenarios
### Typical Use Cases
The LMH1981MT is a specialized clock generator IC designed primarily for video synchronization applications . Its core function is to generate highly stable pixel and line clocks synchronized to an external reference signal.
Primary Use Cases:
- Genlock (Generator Lock) Systems : Synchronizing multiple video sources (cameras, graphics generators) to a common reference (black burst, tri-level sync, or HD/VD signals)
- Video Format Conversion : Providing stable clocking during scan rate conversion (e.g., 1080i to 720p)
- Broadcast Video Equipment : As a clock source for video encoders, frame synchronizers, and production switchers
- Professional Video Interfaces : SDI (Serial Digital Interface) equipment, video capture cards, and broadcast monitors
- Test & Measurement : Video signal generators and analyzers requiring precise clock generation
### Industry Applications
- Broadcast & Television : Master clock generation in OB vans, studios, and post-production facilities
- Medical Imaging : Synchronization of multiple medical video sources (endoscopy, surgical displays)
- Military/Aerospace : Display systems in avionics and ground control stations requiring robust synchronization
- Industrial Vision : Multi-camera machine vision systems where precise timing is critical
- Pro AV : Large-scale video walls, rental/staging equipment, and digital signage with multiple sources
### Practical Advantages
- Wide Frequency Range : Supports SD (Standard Definition), ED (Enhanced Definition), and HD (High Definition) formats from 240p to 1080p
- Flexible Reference Inputs : Accepts composite sync, bi-level/tri-level sync, or separate H/V sync signals
- Low Jitter Performance : Typically < 200ps peak-to-peak, ensuring clean video sampling
- Integrated PLL : Eliminates need for external VCO components in most applications
- Single 3.3V Operation : Simplified power supply design
### Limitations
- Not for Ultra-HD : Maximum output frequency (170 MHz) doesn't support 4K/8K formats
- Analog Tuning Required : Some applications need external filter components for optimal PLL performance
- Limited Output Formats : Primarily provides pixel and line clocks; additional logic may be needed for complex timing signals
- Temperature Sensitivity : May require compensation in extreme environments (-40°C to +85°C operation)
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Reference Signal Integrity Issues
- Problem : Unstable genlock or high jitter due to noisy reference inputs
- Solution :
- Implement proper termination (75Ω for video signals)
- Add low-pass filtering on reference inputs
- Use differential routing for reference signals in noisy environments
Pitfall 2: PLL Instability
- Problem : Clock output drifts or fails to lock
- Solution :
- Carefully select loop filter components per application note
- Ensure reference frequency is within valid range (1 kHz to 170 MHz)
- Provide stable power supply with adequate decoupling
Pitfall 3: Excessive Clock Jitter
- Problem : Visible artifacts in video output
- Solution :
- Use low-ESR decoupling capacitors (0.1 µF ceramic + 10 µF tantalum)
- Separate analog and digital grounds
- Minimize trace lengths to clock outputs
### Compatibility Issues
Power Supply Sequencing
- The LMH198
