SGM9111 Datasheet, PDF (7/9 Pages) SG Micro Corp – 8MHz Rail-to-Rail Composite Video Driver with 6dB Gain

+VS
+VS
+V_S
0.1µF
IN
IN
R_IN ^CIN
SYNC CLAMP
C3
VDC
R1
R₂ R₃
C1
C2
SALLEN KEY LOW
PASS FILTER
R4
R5
R₆
R7
OUT
ROUT = 75Ω _{RL = 75Ω}
GND
SAG NETWORK
Figure 2. AC-Coupled Input/DC-Coupled Output
The Sallen Key Low Pass Filter
The Sallen Key in a classic low pass configuration illustrated in
Figure 1. The filter provides a very stable low pass function,
and in the case of the SGM9111, a 3-pole roll-off at around
8MHz. The 3-pole function is accomplished with an RC low
pass network placed in series with and before the Sallen Key.
One pole provided by the RC network and poles two and three
provided by the Sallen Key for a nice 3-pole roll-off at around
8MHz.
Layout and Power-Supply Bypassing
The SGM9111 operates from single 2.5V to 5.5V supply.
Bypass the supply with a 0.1µF capacitor as close to the pin as
possible. SGMC recommends using microstrip and stripline
techniques to obtain full bandwidth. To ensure that the PC
board does not degrade the device’s performance, design it for
a frequency greater than 1GHz. Pay careful attention to inputs
and outputs to avoid large parasitic capacitance. Whether or
not you use a constant-impedance board, observe the
following design guidelines:
• Do not use IC sockets; they increase parasitic capacitance
and inductance.
• Do not use wire-wrap boards; they are too inductive.
• Use surface-mount instead of through-hole components for
better, high-frequency performance.
• Use a PC board with at least two layers; it should be as free
from voids as possible.
• Keep signal lines as short and as straight as possible. Do not
make 90° turns; round all corners.
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SGM9111