SGM9111ZS Просмотр технического описания (PDF) - Shengbang Microelectronics Co, Ltd

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SGM9111ZS

8MHz Rail-to-Rail Composite Video Driver with 6dB Gain

Shengbang Microelectronics Co, Ltd 

Application Information

The SGM9111 low cost, integrated, 3-pole, video filter is

intended to replace passive LC filters and drivers in low voltage

portable video applications. The 3-pole filter provides better

image quality compared to typical 2-pole solutions.

The SGM9111 input must be AC-coupled because the input

capacitor stores the clamp voltage. It needs a typical value of

0.1µF for the input clamp to meet the Line Droop specification.

The SGM9111 output can drive an AC or DC-coupled doubly

terminated coax (150Ω) load（see Figure 1）. DC-coupling the

output removes the need for an expensive and large output

coupling capacitor（see Figure 2）.

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 SGM9111 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 typical Application diagram of the SGM9111 in Figure 1 is

divided into four sections. The first, Section A is the Sync

Clamp. 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.

+VS

+VS

+VS

0.1µF

IN

IN

RIN CIN

SYNC CLAMP

C3

VDC

R1

R2 R3

C1

C2

SALLEN KEY LOW

PASS FILTER

R4

R5

R6

R7

COUT = 220µF

OUT

ROUT = 75Ω

RL = 75Ω

GND

SAG NETWORK

Figure 1. Typical Application Diagram

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SGM9111

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