DC815A - Demo Manual

DEMO CIRCUIT 815
LT6552
QUICK START GUIDE
LT6552
3.3V Single Supply Video
Difference Amplifier
DESCRIPTION
Demonstration circuit 815 is a Video Line-Driver & Receiver featuring the LT6552. The driver and receiver sections of the board are scored to be separable by the user
so that evaluation with an intermediate cable-run is readily accomplished. Figure 1 shows the general layout of
the board and the usual connections used to perform
evaluations.
The intermediate cable link may be either 75Ω coaxialcable (such as RG-6) or twisted-pair (CAT-5 Ethernet cable). BNC connectors are provided for the coaxial connections, including those for the source and destination
video gear. The twisted-pair option for the intermediate
link uses RJ-45 connections and transports over con-
tacts 7 & 8 (this pair is generally not used in Ethernet
datacom applications and is always straight-through).
Jumpers are provided in the receive section that offer 4
levels of cable-loss equalization, sufficient for CAT-5 cable-runs up to 1000 feet (or 11dB max @ 4MHz).
The Performance Summary table below indicates the key
electrical characteristics provided by this evaluation
board.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
SYMBOL
VS
IS
ZINTX
ZOUTRX
ZOUTTX
PARAMETER
Power Supply Range
Power Supply Current
Video Input Impedance
Video Output Impedance
Line-driver Output Impedance
ZINRX
Line-Receiver Input Impedance
fCU
fCL
EQ
Frequency Response, upper –3dB
Frequency Response, lower –3dB
Line-Receiver Equalization,
Set by Jumpers EQ1 & EQ2
CONDITIONS
No clipping of ac-coupled video
5V, video active, TX & RX total
VIN = 1.0VP-P
VOUT = 1.0VP-P
VOUTTX = 1.0VP-P unbalanced coax
VOUTTX = 1.0VP-P twisted-pair
RX Zin jumper set to 75 ohm
RX Zin jumper set to 110 ohm
any EQ setting
EQ1=OFF, EQ2=OFF (none)
EQ1=ON, EQ2=OFF, f=3.58MHz (≈300’)
EQ1=OFF, EQ2=ON, f=3.58MHz (≈800’)
EQ1=ON, EQ2=ON, f=3.58MHz (≈1000’)
MIN
4.0
TYP
5.0
40
75
75
75
110
75
110
10
5.5
0
3.0
9.0
10.5
MAX
12.6
UNITS
V
mA
Ω
Ω
Ω
Ω
MHz
Hz
dB
OPERATING PRINCIPLES
The LT6552 in location U1 is used as a line-driver that
accepts a differential input and generates a single-ended
output in a gain-of-two configuration. The input provided
is a 75Ω un-balanced connection that may contain sub-
stantial common-mode noise. The output is backterminated to drive either a purely unbalanced 75Ω coaxial link, or a quasi-balanced 110Ω CAT-5 link. The simplified CAT-5 output as implemented here will produce a
1
LT6552
video common-mode on the pair that may be undesirable
in a productized realization, but helps demonstrate the
capability of the receiver function of the DC815. U1 also
demonstrates the compact DFN package.
The LT6552 in the U2 location (in the standard SO-8
package) is set up similarly, except that equalization networks are added to provide cable-loss correction. The
input in this receiver circuit may be terminated in either
75 or 110 ohms, depending on the link media used. The
output is an unbalanced 75Ω output, suitable for driving
standard video equipment. The maximum equalization
circuitry is optimized for 1000’ (300m) CAT-5 cable, providing over 10dB of gain boost at the color sub-carrier
frequency (i.e. 3.58MHz) as shown in Figure 2.
AC-coupling on the inputs and outputs allows the circuitry
to operate from single supplies down to 4V (note that in
dc-coupled video applications, the part is useful down to
3V). The supply and ground connections for the TX and
RX sections are completely isolated so that commonmode ground-noise may be introduced during evaluation
(up to 1.5VPP with 5.0V supplies). The supply current for
each section is typically 20mA with active video present.
Bringing the Shutdown connection(s) to ground will bring
the LT6552(s) into a low-power idle condition.
The Bill-of-Materials is shown in Figure 3 and the schematic diagram of the circuitry in Figure 4.
QUICK START PROCEDURE
Demonstration circuit 815 is easy to set up to evaluate the
performance of the LT6552. Refer to Figure 1 for proper
measurement equipment setup and follow the procedure
below:
1.
7.
Note. The output must be properly loaded with 75Ω, otherwise the signal
will appear doubled in amplitude.
Place jumpers in the following positions:
EQ2 “OFF” position
JP1
EQ1 “OFF” position
JP2
RX Zin “110 ohm” position
JP3
2. With power off, connect the power supply to +5V TX
and +5V RX, and the supply return to GND TX and GND
RX.
3.
Connect a 75Ω video source to TX IN (J2), such as a
camera or pattern generator, and assure that the signal
source is powered and active.
4.
Connect a 75Ω video monitor or signal analyzer to RX
OUT (J6), assuring that the device is powered and
ready to accept video.
5.
Connect a CAT-5 patch cable from TX OUT (J1) to RX
IN (J5).
6.
Turn on the demo circuit power supply.
Note. Make sure that the input voltage does not exceed 12V. All four board
connections must be made to energize the entire circuitry.
2
Check for the proper RX OUT output signal. The output
video waveform should be a high fidelity copy of the
original input (ac-coupled however).
8.
If longer CAT-5 cables are available, such as a full
1000’ (300m) carton with RJ-45 connectors fitted, the
EQ1 and EQ2 jumpers may be repositioned for best
video reproduction.
9.
Evaluation may also be performed with 75Ω coaxialcable as the intermediate link instead of the CAT-5
twisted pair. To do this, remove the CAT-5 cable, move
the JP3 jumper (RX Zin) to the “75 ohm” setting, and
connect the coax link from TX OUT (J3) to RX IN (J4).
Set the EQ1 and EQ2 jumpers for the best video reproduction.
10. In
some instances, it may be desirable to locate the TX
and RX sub-circuits remote from one another to test an
actual link, such as in an elevator car. The DC815 is
scored to allow breaking the board into two standalone
sections in order to place them separately. For shortterm tests, a 9V battery may be used as a power
source for each individual section, should powering be
inconvenient otherwise.
LT6552
Video
Source
Power
Supply
CAT 5 cable,
up to 1000 ft.
(300m)
–
+
Video
Monitor
Figure 1. Proper Measurement Equipment Setup
Figure 2. Receive Equalization Characteristic (max)
3
LT6552
Figure 3. DC815 Bill-of-Material
4
LT6552
Figure 4. DC815 Electrical Schematic Diagram
5
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