QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1016
5V TRIPLE HIGH SPEED VIDEO AMPLIFIER
2
biasing requirements. The outputs are also ac-coupled
to eliminate the amplifier bias from passing to the load.
The dc-biasing at the amplifier inputs is programmed by
the R7 resistor value. The internal input biasing circuitry
behaves as a soft clamp, minimizing the need for exter-
nal components in the signal path. The bias point is rela-
tively fixed and independent of supply voltage changes.
R7 and the input coupling capacitors may be removed if
direct dc drive to the amplifiers is desired.
A jumper, JP1, allows the LT6557 or LT6558 to be forced
to an ENABLE condition. If JP1 is left in the EXTernal
position, then enabling the LT6557 or LT6558 is accom-
plished by pulling down the EN connection at least 2V
below V
+
by connection to E1 or J1. A 40k
Ω
pull-up re-
sistor internal to the IC will provide a default shutdown
mode of operation if the control input is left open-circuit;
this allows open-collector type control of the amplifiers.
A CAL trace is also provided on DC1016 to provide a
means of precision calibration for a Network Analyzer
(use the CAL connections when performing the “THRU”
transmission calibration). The CAL trace has the same
electrical performance and delay as the transmission
lines of the three signal channels, thereby allowing most
circuit board and connector effects to be eliminated from
the transmission measurements.
Figure 4 shows the material list of the components used
by DC1016, and Figure 5 shows the electrical intercon-
nection.
QUICK START PROCEDURE
Demonstration Circuit 1016 is easy to set up to evaluate
the performance of the LT6557 or LT6558. Refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below:
NOTE:
Due to the Ultra High Frequencies (UHF) involved,
RF measurement practices are required to accurately
evaluate the performance of the board.
1.
Place jumpers in the following positions:
ENABLE
2.
Prior to connecting the power supply, preset the out-
put voltage to +5V, or to the desired level, if different.
3.
With power off, connect the power supply to V
+
and
GND using banana-plug cables.
4.
If using a Network Analyzer, perform the THRU
transmission cal with all cabling, adapters, impedance
converters, etc. in place, and using the DC1016 CAL
trace as the reference 0dB path.
5.
Energize the power supply.
6.
Connect the Network Analyzer (if used) to the appro-
priate channels to measure frequency response and
crosstalk as desired. Figure 2 shows a typical trans-
mission plot.
7.
For video-signal evaluation, connect a component-
video signal source to the inputs and a monitor and/or
video analyzer to the outputs, using equal-length ca-
bling amongst the three video channels. Figure 3
shows a typical pulse response.
8.
To evaluate the shutdown mode, disconnect or relo-
cate the JP1 jumper to the EXT position (with no con-
nections made at EN, or if present, a logic high pro-
vided).
JP1
