Six Channel, 6th Order SD/HD Video Filter Driver# Technical Documentation: FMS6346MTC20 Video Filter Driver
Manufacturer : FSC (Fairchild Semiconductor)
Component Type : Triple 6th-Order SD (Standard Definition) Video Filter with 6dB Gain and Input Sync Tip Clamp
Package : TSSOP-20
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## 1. Application Scenarios
### Typical Use Cases
The FMS6346MTC20 is a specialized analog video signal processor designed for conditioning composite video signals in standard definition (SD) systems. Its primary function is to reconstruct and buffer video signals after digital-to-analog conversion (DAC) stages.
Primary Applications Include:
- Set-Top Boxes (STBs) and Digital TV Receivers : Filters and drives analog composite video outputs from MPEG decoders or other video processors. It is commonly used to generate CVBS (Composite Video Baseband Signal) outputs for connection to legacy televisions or recording devices.
- DVD/Blu-ray Players and Media Players : Provides clean, compliant analog video outputs from the player's internal video DACs, ensuring proper signal levels and bandwidth limiting to meet broadcast standards.
- Video Game Consoles (Legacy Systems) : Conditions the RGB or YPbPr signals converted to composite video, ensuring output signals meet standard specifications for direct TV connection.
- PC Video Capture/Output Cards : Used on add-in cards to generate high-quality, stable analog video outputs for presentations or secondary displays.
- Security DVR Systems : Filters the analog video output for local monitoring on standard definition monitors.
### Industry Applications
This component is prevalent in consumer electronics, broadcast equipment, and industrial video distribution systems where reliable, high-fidelity SD analog video output is required. It is particularly crucial in cost-sensitive, high-volume applications due to its integration and performance.
### Practical Advantages and Limitations
Advantages:
* High Integration : Combines three independent 6th-order filters (typically for Y, C, and CVBS channels) with fixed 6dB gain buffers and DC restoration clamps in a single 20-pin package, reducing board space and component count.
* Excellent Performance : The 6th-order Butterworth filter provides a sharp roll-off (~36dB/octave) at 8MHz, effectively attenuating DAC sampling images and high-frequency noise while maintaining minimal group delay variation in the passband. This preserves video sharpness and color fidelity.
* Built-in Sync Tip Clamp : Each channel includes an input clamping circuit that sets the sync tip level to a fixed voltage (typically ground-referenced). This ensures stable video black level regardless of source coupling or minor DC offsets, critical for consistent picture brightness.
* Low Output Impedance : Capable of driving doubly-terminated 75Ω coaxial cables (150Ω load) to standard 1Vpp levels, making it directly compatible with standard video infrastructure.
* Low Power Consumption : Designed for single +5V supply operation with typical supply currents under 30mA, suitable for portable and power-conscious designs.
Limitations:
* Fixed Functionality : The filter characteristics (cutoff frequency, gain) are fixed. It cannot be used for other filter types (e.g., low-pass at different frequencies, high-pass) or variable gain applications without external circuitry.
* Standard Definition Only : The 8MHz bandwidth is optimized for SD formats (e.g., NTSC, PAL). It is not suitable for processing HD (High Definition) component or VGA signals, which require much higher bandwidth.
* Single Supply Constraint : While convenient, the +5V single-supply operation limits the output swing headroom. Care must be taken to prevent clipping on full-white video signals, especially when driving heavy loads.
* AC-Coupled Input Requirement : The internal clamp circuit requires the input signal to be AC-coupled via an external
