feature

8-BIT resolution 150 megapixels per second 0.2% Linearity Error Sync and Blank Control 1.0v pp video into 37.58486 or 758486load; Internal Bandwidth Voltage Reference Low Distortion Double Buffered Data TTL-Compatible Input Low Glitch EnergySingle+5 volt power supply

application

Video Signal Conversion-RGB-YCBCR Composite Multimedia System Image Processing True-color graphics systems

illustrate

FMS3810/ This is cropped for making graphics and video applications. Speed is the key. Two speed grades are available:

TTL level input converted to analog current output can drive 25–37.5Ω load, corresponding to double-terminated 50–75Ω load. The synchronization current is added to the IOG output after the synchronization input timing. Blank will override RGB input when blank=L. Although suitable for many applications the internal 1.235V reference voltage can be input via VREF. Few external components are required, just a current reference resistor, current output load resistor, and decoupling capacitors. The package is a 48 lead LQFP. The manufacturing technology is CMOS. Performance is guaranteed between 0 and 70°C.

Functional description: There are three identical 10-bit D/A converters in the FMS3810/3815, each with a current source output. External loads need to convert current to voltage output. Data inputs RGB7-0 are overwritten with blank inputs. sync=H to activate, sync current from IOS to sync signal on green video. Digital Inputs All digital inputs are TTL compatible. Data is registered on the rising edge of the CLK signal. The next stage pipeline delay, the analog output rises after the time difference changes the edge of CLK. Sync and Blank The Sync and Blank inputs control the D/A converter interval in the output level. Blank forces the D/A output to be blanked. When SYNC=L closes the green D/A converter. SYNC=H adds a 40IRE sync pulse to the green output, sync=L sets the output to 0.0 volts during the green sync prompt. Sync and blank are registered on the rising edge of CLK.

Blank gate D/A input and set base voltage. If blank=H, the D/A input is added to the offset current output. If blank=L, data entry and base are disabled. D/A Outputs Each D/A output is a current source. To get the voltage output, the resistor must be connected to ground. The output voltage depends on the external resistor voltage, and the value of the gain setting resistor connected between RREF and GND. Typically, a 75 ohm source termination resistor is placed between the D/A current output pin and GND near the D/A converter. A 75 ohm line might be connected to the far end of the cable with another 75 ohm terminating resistor. This "double terminated" means a D/A converter with a net resistive load of 37.5 ohms. The FMS3810/3815 can also be terminated with a 75 ohm resistor. To reduce the output voltage swing within the desired range, the nominal value of the resistor, RREF, should be doubled.

Voltage References All three D/A converters are equipped with a voltage reference. The internal bandgap voltage reference is +1.235V, and the supply resistance is 3KΩ. An external voltage reference can be connected to the VREF pin to override the internal voltage reference. A 0.1µF capacitor must be connected between the compressors to stabilize the internal bias circuit and ensure low noise operation. The power required for power and ground is a single supply +5.0 volts. To minimize power supply induced noise, the analog +5V is connected to the VDD pin through 0.1 and 0.01µF decoupling capacitors placed near each VDD pin or pin pair. The high conversion rate of digital data makes capacitive coupling of the output of any D/A converter a potential problem. Since the digital signal contains the CLK signal as well as the video output signal data feedthrough often looks like harmonic distortion or degrades the SNR performance. All ground pins should preferably be connected to a common solid ground plane performed.

Application Information: The figure shows a typical FMS3810/3815 interface circuit. In this example, the optional 1.2V bandgap reference is connected to the VREF output, overriding the internal voltage reference source. The grounded FMS3810/3815 power supply must be well regulated and free of high frequency noise. Careful decoupling of the power supply will ensure the highest quality video signal at the output of the circuit. The FMS3810/3815 have separate analog and digital circuits. To keep digitizing system noise from the D/A converter, it is recommended that the supply voltage (VDD) come from the system analog power supply and all ground connections (GND) to the analog ground. The power pins should be separate on the pins. Printed Circuit Board Layout The design of high-performance mixed-signal circuits requires printed circuits with ground planes. The layout of the overall system board has a great impact on performance. Capacitive coupling from digital to analog circuits can lead to poor D/A conversion. Consider this advice when laying out:

1. Keep key analog traces (VREF, IREF, COMP, IOS, IOR, IOG) as short as possible. All digital signals are possible. The FMS3810/3815 should be located near the edge of the board, near the analog output connectors.

2. The power plane of the FMS3810/3815 should be separate from the one that provides the digital circuit. All VDD should use one power board pin. If the power supply of the FMS3810/3815 is the same as the digital circuit of the system, the FMS3810/3815 should be isolated with 0.1µF and 0.01µF capacitors with ferrite beads.

3. The ground plane should be solid, not cross hatched. The connection to the ground plane should be very short lead.

4. If the digital power supply has a dedicated power supply board, it should not be placed under the FMS3810/3815, voltage reference or analog output. Capacitive digital supply noise coupling from this layer into the FMS3810/3815 and its associated analog circuitry can adversely affect performance.

5. CLK should be handled with care. Jitter and Noise Turning this clock on can degrade performance. Terminate the clock lines carefully to eliminate overshoot and ringing.

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