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TPF1441C

72M HD Composite Video Filter Driver with Clamped input Comparator

Application Information

The TPF1441C is targeted for systems that require 1 channel high-definition (HD) video outputs. Although it can be used for

numerous other applications, the needs and requirements of the video signal are the most important design parameters of the

TPF1441C. The TPF1441C incorporates many features not typically found in integrated video parts while consuming very low power.

Internal Sync Clamp

The typical embedded video DAC operates from a ground referenced single supply. This becomes an issue because the lower

level of the sync pulse output may be at a 0V reference level to some positive level. The problem is presenting a 0V input to most

single supply driven amplifiers will saturate the output stage of the amplifier resulting in a clipped sync tip and degrading the video

image. A larger positive reference may offset the input above its positive range.

The TPF1441C features an internal sync clamp and offset function to level shift the entire video signal to the best level before it

reaches the input of the amplifier stage. These features are also helpful to avoid saturation of the output stage of the amplifier by

setting the signal closer to the best voltage range.

The simplified block diagram of the TPF1441C is on Page-2. The AC coupled video sync signal is pulled negative by a current

source at the input of the comparator amplifier. When the sync tip goes below the comparator threshold the output comparator is

driven negative, The PMOS device turns on clamping sync tip to near ground level. The network triggers on the sync tip of video

signal.

Comparator Internal Clamp

TPF1441C integrates a comparator, which supports UTC function monolithically. Because of the distortion of the control signal

transmitted over a long cable, the rising/falling edges would become slower and the amplitude would be attenuated. Furthermore the

DC component may be shifted due to inconsistent DC ground level between sending and receiving devices. In a traditional design,

the reference of the comparator needs to be manually changed accordingly. In order to solve this application problem, TPF1441C

implements a new feature on the input of comparator which clamps the bottom level of the input signal to 40.0 mV. Therefore, there

is no need to consider the DC shift issue when choosing reference level, making the choice of reference level easier. Note that, to

use this feature, the input must be AC-coupled and the capacitor selection is based on the control signal bandwidth. Typically a 0.1uF

capacitor is used..

Reference = 40mV +

Threshold

Input with AC couple

VCC

Droop Voltage and DC Restoration

Selection of the input AC-coupling capacitance is based on the system requirements. A typical sync tip width of a 64μs NTSC