QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1016
5V TRIPLE HIGH SPEED VIDEO AMPLIFIER
LT6557 / LT6558
DESCRIPTION
Demonstration Circuit 1016 (DC1016) is a 5V Triple High
Speed Video Amplifier featuring the LT6557 or LT6558 in
DFN packaging. The DC1016A–A version demonstrates
the gain-of-two LT6557, while the DC1016A–B features
the unity-gain LT6558. The board is designed to demon-
strate AC-coupled performance in 5V single-supply op-
Table 1. Performance Summary (T
A
= 25°C)
PARAMETER
Supply Voltage
Supply Current
Input Impedance, INR, ING, INB
Output Impedance, OUTR, OUTG, OUTB
CAL trace Impedance
Gain (–A version)
Outputs terminated into 75Ω
Outputs terminated into High impedance
Outputs terminated into 75Ω
Outputs terminated into High impedance
V
IN
= 125mV
PP
(-16dBm), –3dB, R
L
=75Ω
V
IN
= 125mV
PP
(-16dBm), ±0.1dB, R
L
=75Ω
Worst-case All Hostile, 10MHz
Worst-case All Hostile, 100MHz
+5.0V Supply, No Output Clipping
Logic Low Voltage (Amplifiers ON)
Logic High Voltage (Amplifiers OFF)
CONDITION
Recommended Min/Max
V
+
= 5V
VALUE
+5V/+10V
65mA
75Ω to ground, ac-coupled internal
signals
75Ω, ac-coupled
75Ω nominal
0dB nominal
+6dB nominal
–6dB nominal
0dB nominal
7Hz to 380MHz typical
7Hz to 130MHz typical
–75dB typical
–55dB typical
±0.6V about average dc (–A)
±1.2V about average dc (–B)
≤ (V
– 2)V
+
eration. The LT6557 and LT6558 include automatic in-
ternal biasing that is programmable with one resistor.
Table 1 indicates the performance that is achieved with
this evaluation board.
Design files for this circuit board are available. Call
the LTC factory.
Gain (–B version)
Frequency Response
Crosstalk
Input Signal Voltage Range
On/Off Control Input
≥ (V
– 0.5)V or open circuit
+
OPERATING PRINCIPLES
DC1016 provides three identical channels of wideband
signal amplification suitable for driving HDTV or high-
resolution RGB video display cables. The LT6557 pro-
vides a gain of two for driving terminated video cables
and the LT6558 has unity gain for use with high-
impedance loads. Each amplifier section is provided with
series “back-termination” at the outputs (included on the
board), which results in unity gain transmission of a
video signal to a destination load (75Ω for –A; 1kΩ or
more for –B). Each input is dc terminated to analog
ground to properly load the input signal cable. The in-
puts are ac-coupled after termination to eliminate input
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1016
5V TRIPLE HIGH SPEED VIDEO AMPLIFIER
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 40kΩ 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
converters, etc. in place, and using the DC1016 CAL
trace as the reference 0dB path.
5.
6.
Energize the power supply.
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.
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.
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).
to the Ultra High Frequencies (UHF) involved,
RF measurement practices are required to accurately
evaluate the performance of the board.
Place jumpers in the following positions:
JP1
ENABLE
Prior to connecting the power supply, preset the out-
put voltage to +5V, or to the desired level, if different.
With power off, connect the power supply to V
+
and
GND using banana-plug cables.
If using a Network Analyzer, perform the THRU
transmission cal with all cabling, adapters, impedance
1.
7.
2.
3.
4.
8.
2
Analog electronics
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