rc6303 Fairchild Semiconductor, rc6303 Datasheet - Page 5

• Manufacturer Part Number: rc6303
• Description: Triple Video Amplifier With Separate Enable Inputs
• Manufacturer: Fairchild Semiconductor

PRODUCT SPECIFICATION
Applications Discussion
Each of the three sections of the RC6303 is provided with an
Enable input, thus the part is useful for selecting and multi-
plexing. A three-channel video multiplexer can be built with
just one RC6303 and a decoder, as shown in Figure 1.
Note that RC6303 enable time is shorter than its disable
time, hence a make-before-break action is provided, mini-
mizing switching transients on the signal output.
An RGB switch is shown in Figure 2.
Capacitive Load
The RC6303 can drive a capacitive load from 10 to over 100
pF. In back terminated video applications, bandwidth will
only be limited by the RC time constants of the external out-
put components. A minimum 10 pF capacitive load is
required. When driving a 75 cable, place the 75 source
termination resistor as close to the amplifier output as possi-
ble.
Enable/Disable
The enable pins (10, 12, 14), when pulled to a TTL or
CMOS logic low or when tied to ground, activate each
amplifier individually. When pulled to a TTL or CMOS logic
high, the amplifier is tri-stated and presents a high imped-
ance at its output. When disabled the amplifier's power con-
sumption drops, and the non-inverting input signal is isolated
from its respective output.
DC Accuracy
Since the RC6303 is a voltage-feedback amplifier, the invert-
ing and non-inverting inputs have similar impedances and
bias currents. To minimize offset voltage, match the source
resistances seen by inverting and non-inverting inputs.
Feedback Components
Because the RC6303 is a voltage-feedback amplifier, it facil-
itates using reactive (capacitive and inductive) feedback
components for implementing filters, integrators, sample/
hold circuits, etc. The feedback network and the parasitic
capacitance at the inverting (summing junction) input create
a pole and affect the transfer function of the circuit. For sta-
ble operation, minimize the parasitic capacitance and equiva-
lent resistance of the components used in the feedback
circuit.
Circuit Board
High-frequency applications require good grounding, power
supply decoupling, low parasitic capacitance and inductance,
and good isolation between the inputs to minimize their
crosstalk. Avoid coupling from output to input to prevent
positive feedback.
Channel a
Blue Input
Channel a
Green Input
Channel
Select
Channel 3
Input
Channel a
Red Input
Channel 2
Input
+
–
B
Channel 1
Input
–
+
G
+
–
+
–
R
B
Video Busses
Figure 1.
Figure 2.
+
74LS04
–
Decoder
R G
G
B
+
–
R
R
–
+
G
–
+
Channel b
Red Input
B
–
+
Channel b
Green Input
Output
65-7460
Channel b
Blue Input
65-7461
RC6303
5