Features and Benefits
- Low Cost, Integrated Solution
- +5 V Operation
- Accepts FSC Clock or Crystal, or 4 FSC Clock
- Minimal External Components:
- No External Filters or Delay Lines Required
- Onboard DC Clamp
- Accepts Either HSYNC and VSYNC or CSYNC
- Composite Video and Separate Y/C (S-Video) Outputs
- Luma and Chroma Outputs Are Time Aligned
- Phase Lock to External Subcarrier
- Drives 75 Ω Reverse-Terminated Loads
- Logic Selectable NTSC or PAL Encoding Modes
- Compact 16-Lead SOIC
The AD724 is a low cost RGB to NTSC/PAL Encoder that converts red, green and blue color component signals into their corresponding luminance (baseband amplitude) and chrominance (subcarrier amplitude and phase) signals in accordance with either NTSC or PAL standards. These two outputs are also combined to provide composite video output. All three outputs can simultaneously drive 75 (ohm), reverse-terminated cables. All logical inputs are CMOS compatible. The chip operates from a single +5 V supply. No external delay lines or filters are required. The AD724 may be powered down when not in use.
The AD724 accepts either FSC or 4FSC clock. When a clock is not available, a low cost parallel-resonant crystal (3.58 MHz (NTSC) or 4.43 MHz (PAL)) and the AD724’s on-chip oscilla-tor generate the necessary subcarrier clock. The AD724 also accepts the subcarrier clock from an external video source.
The interface to graphics controllers is simple: an on-chip logic “XNOR” accepts the available vertical (VSYNC) and horizontal sync (HSYNC) signals and creates the composite sync (CSYNC) signal on-chip. If available, the AD724 will also accept a standard CSYNC signal by connecting VSYNC to +5 V and applying CSYNC to the HSYNC pin. The AD724 contains decoding logic to identify valid horizontal sync pulses for correct burst insertion.
Delays in the U and V chroma filters are matched by an on-chip sampled-data delay line in the Y signal path. To prevent aliasing, a prefilter at 5 MHz is included ahead of the delay line and a post-filter at 5 MHz is added after the delay line to suppress harmonics in the output. These low-pass filters are optimized for minimum pulse overshoot. The overall luma delay, relative to chroma, has been designed to be time aligned for direct input to a television’s baseband. The AD724 comes in a space-saving SOIC and is specified for the 0°C to +70°C commercial temperature range.
An evaluation board is available for this product and may be ordered using the following product number: AD724-EB.
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Software & Systems Requirements
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
Sample & Buy
The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.