feature

7.1 MHz 5th order Y, C filter with compound summer selectable 0dB or 6dB gain MHz No external frequency select components or <5ns group delay skew on clock Y, C and CV outputs AC coupled input AC or DC coupled outputs Ability to select PAL frequency components or 0.3%/0.2° differential on clock Y, C and CV channels Gain/Phase Integrated Low Slope DC Restoration Circuit Lead Free SOIC-8 Package

application

Cable and satellite set-top boxes DVD players Personal video recorders (PVR) Video on demand (VOD)

illustrate

The FMS6400 is a dual Y/C fifth-order Butterworth low-pass video filter optimized for minimal overshoot and flat group delay. The device also contains a summing circuit to generate the filtered composite video. In a typical application, the Y and C input signals from the DAC are AC coupled into the filter. Both channels have DC restoration circuitry to limit the DC input level during video sync. Y and C channels use separate feedback clamps. The clamp pulse is from the Y channel. All outputs can drive 2Vpp, AC or DC coupled, into single or dual video loading. A single video load consists of a series 75Ω impedance matching resistor connected to a terminated 75Ω line. This represents a total load section of 150 Ω. A double load is two in parallel showing a total of 75Ω to the part. The gain signal of Y, C and CV can be selected as 0dB or 6dB with 1Vpp input level. All during synchronization, the video channel is clamped to establish the proper output voltage reference level. The typical cutoff frequency for the FMS6400 is 7.1MHz. The a option provides a lower cutoff frequency of 5MHz.

DC characteristics

Tc=25°C, Vcc=5V, Vin=1Vpp, ASEL=1 (6dB gain), all inputs AC-coupled 0.1uF, all outputs AC-coupled 220uF into 150Ω load, referenced to 400kHz; unless otherwise noted.

AC Electrical Characteristics

Tc=25°C, Vcc=5V, Vin=1Vpp, ASEL=1 (6dB gain), all inputs AC-coupled 0.1uF, all outputs AC-coupled 220uF into 150Ω load, referenced to 400kHz; unless otherwise noted.

Application Information Functional Description: This product is a dual-channel monolithic continuous-time video filter for reconstructing luminance and chrominance signals from S-Video D/A sources. The composite video output is generated by summing the Y and C outputs. The chip is designed to be AC-coupled input, and will work equally well for AC or DC-coupled output. The reconstruction filter provides a 5th order Butterworth group delay equalization response. This provides the most flat response in terms of delay and amplitude. Each of the three outputs is capable of driving 2Vpp into a 75Ω load. During the sync interval, all channels are clamped to set the appropriate minimum output DC level. The effective input time constant is greatly reduced in this operation, which enables the use of small, low-cost coupling capacitors. The net effect is that for any DC shift, the input will settle to 10mV in 10ms to appear in the input video signal. In most applications, the input coupling capacitor is 0.1µF. The Y and C inputs typically draw 1µA of current during active video, and the horizontal line typically slopes 2mV at the Y output. During synchronization, the clamp was sourced by averaging 20 μA over the clamping interval. Any change in the coupling capacitor value will affect the tilt of each row. Any decrease in tilt is accompanied by an increase in settling time.

Luminance (Y) I/O The typical luma input is driven by a low impedance 1Vpp source or the output of a 75Ω terminated line is driven by the output of the current DAC. In either case, the input must be capacitively coupled to allow the synchronization detection and DC recovery circuits to function properly. All outputs can drive 2Vpp, AC or DC coupled, into single or dual video loading. A single video load consists of a series 75Ω impedance matching resistor connected to a 75Ω terminated line, which will connect to the section. A double load is two in parallel showing a total of 75Ω to the part. Channel gain of 0dB on all channels is available by connecting select pin 2 to ground. Channel gain of 6dB on all channels is selected by connecting pin 2 to VCC. Both gain settings assume a standard input video level of 1Vpp. Chroma (C) I/O The chrominance input is driven in the same way as the luma input, but is usually only a 0.7Vpp signal. Since the chrominance signal does not contain any DC components, an AC coupling capacitor as small as 0.1 μF can be used for the output signal, if DC coupling is not required.

Composite Video (CV) Output The composite video output driver is the same as the other outputs. Layout Considerations General floor plan and supply bypass play an important role in high-rise building frequency performance and thermal characteristics. Fairchild provides a demo board, the FMS6400DEMO, for use as a guide for device testing and characterization. The FMS6400DEMO is a 4-layer board with full power and ground planes. For best results, follow the steps below for a high frequency layout basis:

10µF and 0.1µF ceramic bypass capacitors included

Place 10µF capacitors within 0.75" of the power pins

Place 0.1µF capacitors within 0.1" of the power pins

If using DC-coupled outputs, use a large ground plane to help dissipate heat

Minimize all trace lengths to reduce series inductance