Linear LT6557, LT6558 Quick Start Manual
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1016
DESCRIPTION
5V TRIPLE HIGH SPEED VIDEO AMPLIFIER
LT6557 / LT6558
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 demonstrate AC-coupled performance in 5V single-supply op-
Table 1. Performance Summary (TA = 25°C)
PARAMETER CONDITION VALUE
Supply Voltage Recommended Min/Max +5V/+10V
Supply Current V+ = 5V 65mA
Input Impedance, INR, ING, INB
Output Impedance, OUTR, OUTG, OUTB 75Ω, ac-coupled
CAL trace Impedance 75Ω nominal
Gain (–A version)
Gain (–B version)
Outputs terminated into 75
Outputs terminated into High impedance +6dB nominal
Outputs terminated into 75
Outputs terminated into High impedance 0dB nominal
eration. The LT6557 and LT6558 include automatic internal 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.
75Ω to ground, ac-coupled internal
signals
Ω
Ω
0dB nominal
–6dB nominal
V
= 125mVPP (-16dBm), –3dB, RL=75Ω 7Hz to 380MHz typical
Frequency Response
Crosstalk
Input Signal Voltage Range +5.0V Supply, No Output Clipping
On/Off Control Input
IN
V
= 125mVPP (-16dBm), ±0.1dB, RL=75Ω 7Hz to 130MHz typical
IN
Worst-case All Hostile, 10MHz –75dB typical
Worst-case All Hostile, 100MHz –55dB typical
Logic Low Voltage (Amplifiers ON)
Logic High Voltage (Amplifiers OFF)
OPERATING PRINCIPLES
DC1016 provides three identical channels of wideband
signal amplification suitable for driving HDTV or highresolution RGB video display cables. The LT6557 provides a gain of two for driving terminated video cables
and the LT6558 has unity gain for use with highimpedance 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 inputs are ac-coupled after termination to eliminate input
±0.6V about average dc (–A)
±1.2V about average dc (–B)
≤ (
V+– 2)V
≥ (
V+– 0.5)V or open circuit
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1016
JP1
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 external components in the signal path. The bias point is relatively 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 accomplished by pulling down the EN connection at least 2V
below V+ by connection to E1 or J1. A 40kΩ pull-up re-
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 output 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
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 interconnection.
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 appropriate channels to measure frequency response and
crosstalk as desired. Figure 2 shows a typical transmission plot.
7.
For video-signal evaluation, connect a componentvideo signal source to the inputs and a monitor and/or
video analyzer to the outputs, using equal-length cabling amongst the three video channels. Figure 3
shows a typical pulse response.
8.
To evaluate the shutdown mode, disconnect or relocate the JP1 jumper to the EXT position (with no connections made at EN, or if present, a logic high provided).
2
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