SGM9121 Datasheet, PDF (7/11 Pages) SG Micro Corp – 5th-Order Video Driver with 6dB Gain

SGM9121
APPLICATION INFORMATION
The SGM9121 low cost, integrated, 5th-order video filter
is intended to replace passive LC filters and drivers in low
voltage portable video applications.
The SGM9121 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 SGM9121 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). If an AC-coupled output is needed, the SAG
correction circuit can be used to reduce the AC output
coupling capacitor value.
Offering SAG correction, fixed gain of 6dB, and a 5th-
order low pass filter in a tiny space saving package
makes the SGM9121 well suited for space sensitive
applications such as digital cameras, cellular phones and
other portable devices.
Enable/Shutdown
The SGM9121 has a shutdown feature that disables the
output and reduces the quiescent current to 0.72μA. This
feature is particularly useful in portable applications, such
as video cameras, hand held gaming devices and cellular
phones, where video filtering and driving capability are
required.
8MHz, 5th-Order Video Driver
with 6dB Gain
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 that 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 SGM9121 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 optimal voltage range.
The Typical Application Diagram of the SGM9121 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 comparator output is driven
negative, and the PMOS device turns on, clamping sync
tip to near ground level. The network triggers on the sync
tip of video signal.
IN
R_IN
V_CC = 3.0V to 5.5V
To External Power
Supply or Control I/O
0.1µF
C_IN
10kΩ
V_CC
5th-Order
Filter
Level
Shifter
DISABLE
OUT
6dB
SAG
SGM9121
C_OUT
47µF
CS
22µF
GND
Figure 1. AC-Coupled Input/AC-Coupled Output
R_OUT
75Ω _{75Ω RL}
SG Micro Corp
www.sg-micro.com
7