DC1108A - Demo Manual

DEMO CIRCUIT DC1108 QUICK START GUIDE
DEMO CIRCUIT 1108
650MHZ DIFF. ADC DRIVER / DUAL SELECTABLE-GAIN
AMPLIFIER
QUICK
START GUIDE
LT6411
650MHz Differential ADC
Driver / Dual Selectable
Gain Video Amplifier
DESCRIPTION
Demonstration circuit 1108 features the LT6411 Dual Amplifier and ADC Driver. It incorporates a variety of passive
components to support configurations for varied applications, including large AC-coupling capacitors for video applications. Single-ended or differential input and output configurations are possible with on-board component changes.
The LT6411 supports both a single +5V power supply as
well as split ±5V supplies.
The LT6411 is a high-speed differential amplifier with superior distortion and noise performance, perfect for demanding video distribution, communications, and other high-
speed signal chain applications. The LT6411 accepts singleended or differential inputs with almost no difference in distortion performance. The topology of the LT6411 allows the
flexibility of selecting various gains without the use of extra
resistors. The LT6411 consumes only 16mA of supply current (80mW) when enabled, and includes a low-power
shutdown mode for additional power savings.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
QUICK START PROCEDURE
Table 1 shows the function of each SMA connector on the
board. Refer to Figure 1 for the connection diagram and
follow the procedure below:
1. Connect the power supply as shown. The power labels of
VCC and GND are used to apply a single +5V to +10V
supply; by default, VEE is connected to GND through resistor R21. Jumper JP1 enables or shuts down the
LT6411.
2. Apply an input signal to J1. A low-distortion, low
noise signal source with an external high-order filter
will yield the best performance. DC1108’s input is
impedance-matched to 75Ω; no external termination
is necessary. To use a 50Ω source instead of a 75Ω
source, replace impedance-matching resistor R6
with a 57.6Ω 0603 resistor.
3. Observe the output via J2 and/or J3. The default gain is
+2, relative to the single-ended input. The outputs have
75Ω series resistors.
Table 1: DC1108 SMA Connector Descriptions
CONNECTOR FUNCTION
J1 (IN1)
Board Input. Use this connector to supply an input to
the DC1108. Drive from a 75Ω signal source, no external termination necessary. Resistor R6 provides a 75Ω
impedance match. Input is AC coupled by default.
J4 (IN2)
Board Input. Connected to GND through resistor R20 by
default. Resistor can be removed to drive the DC1108
differentially. Input is AC coupled by default.
J2 (OUT1)
J3 (OUT2)
Output. By default, connected by a 75Ω series resistor
for video cable driving.
Output. By default, connected by a 75Ω series resistor
for video cable driving.
1
DEMO CIRCUIT DC1108 QUICK START GUIDE
650MHZ DIFF. ADC DRIVER / DUAL SELECTABLE-GAIN AMPLIFIER
Power Supply (+5V)
Optional Supply (-5V)
(Remove R21)
Input (Z = 75Ω)
Differential Output
with 75Ω series
resistors for cable
driving
Figure 1. DC1108 Default Board Evaluation Setup – Single Ended Input, AC-Coupled. Gain = +2
Figure 2. Block Diagram of LT6411 Internal Amplifiers and Resistors
2
DEMO CIRCUIT DC1108 QUICK START GUIDE
650MHZ DIFF. ADC DRIVER / DUAL SELECTABLE-GAIN AMPLIFIER
Figure 3. Input and Output Networks of the DC1108 Demo Board
ADDITIONAL INFORMATION
Although the DC1108 demo board is ready to use out of
the box, it has features that you can access by adding, removing or changing components on the board. These are
described below.
ENABLE (SHUTDOWN)
The enable (shutdown) function of the LT6411 is controlled
by JP1. To enable the part, move the on-board JP1 jumper
to the lower (EN) position. To place the driver in a lowpower shutdown mode, move the jumper into the upper
(DIS) position.
NOTE. The input bias resistors R2/R3 and R17/R18 enable
current flow from VCC to GND, and must be accounted for
when measuring the current of the LT6411, especially in
shutdown.
GROUND AND VEE CONNECTIONS
DC1108’s GND connector is connected to the board’s
ground planes. By default, VEE is also connected to the
ground planes via R21. However, the LT6411 is capable of
running on up to 10V power supply voltage (or ±5V).
Therefore, the LT6411 VEE pins and exposed paddle are
floating, and connected to the ground plane through bypass capacitors. By removing R21 and powering the
LT6411 through the VEE turret (E3), the user can provide
split supplies to the LT6411.
INPUT AND OUTPUT VOLTAGE RANGES
The input range of the LT6411 (Pins 13 and 16) extends
from 1V above VEE to 1V below VCC. The inverting inputs, Pins 14 and 15, do not have this limitation, and can
be driven from rail to rail. The outputs, Pins 8 and 5, can
swing to within 1.3V of either supply (less under heavy
load). These ranges can be limiting factors, especially
when using DC1108 without the AC-coupling capacitors.
3
DEMO CIRCUIT DC1108 QUICK START GUIDE
650MHZ DIFF. ADC DRIVER / DUAL SELECTABLE-GAIN AMPLIFIER
By default, R17 and R18 set the LT6411 input/output
common-mode voltage to 2.1V, which is the LT6411’s
lowest-distortion bias point (see datasheet, page 10).
SPARE COMPONENTS
DC1108 comes with spare components for use when
evaluating different circuit configurations. C6, R23, and
R24 are an extra 220µF capacitor and 0Ω resistors, re-
spectively. See the next section below (Flexible Configurations) for some examples of possible configurations for the LT6411 on DC1108.
FLEXIBLE CONFIGURATIONS
The LT6411 is a dual amplifier with internal gain and feedback-setting resistors. This simple, intuitive topology allows the user to test many different circuit configurations
on DC1108 simply by changing the resistors on the board.
Refer to Figure 3 for the networks at the inputs and outputs
of the LT6411. Table 2 describes only some of the myriad
configurations possible on DC1108. Contact the LTC factory for assistance with any of these configurations, or if
your configuration needs differ from what is shown.
For DC-coupled configurations, C2, C3, and C4 can be replaced by 1206-size surface mount resistors.
SETTING DGND
The DGND pin (Pin 12) is the reference voltage for the
Enable Low pin (Pin 11). On a single +5V supply,
when the EN pin is pulled to within 0.4V of the DGND
pin, the part is enabled. However, there are two restrictions on the voltage compliance of the DGND pin,
which is discussed in the datasheet:
DGND should be tied to VEE. On the board, removing
R22 and populating R26 will accomplish this adjustment.
Table 2: Example DC1108 Configurations
FUNCTION
CONFIGURATION
VIDEO AMPLIFIER, LINE OR ADC DRIVER CONFIGURATIONS
No changes necessary
Single Ended Input
(default)
Gain = +2
AC-Coupled
Differential Outputs
Remove R6.
Single Ended Input
Install 37.5Ω at R5.
Gain = +1
Install 40.2Ω at R3.
AC-Coupled
(resistors attenuate and Z-match to 75Ω)
Differential Outputs
Remove R6, R20 (or use for Z-Match).
Differential Input
Remove R12 and C3.
Gain = +1
Install R2, R3 to match R17, R18.
AC-Coupled
Install 0Ω at R7 and R15.
Differential Outputs
Remove R6, R20 (or use for Z-Match).
Differential Input
Remove R7.
Gain = +2
Install R2, R3 to match R17, R18.
AC-Coupled
Install 220µF at C3.
Differential Outputs
Remove R6, R20 (or use for Z-Match).
Differential Input
Remove C3, R7 and R12.
Gain = +3
Install R10 and R25 (0Ω).
AC-Coupled
Differential Outputs
VIDEO SIGNAL SPLITTER
Remove R20 and/or C4.
Single Ended Input
Install R11 (0Ω).
Gain = +1
Remove R12 and C3.
AC-Coupled
Install 0Ω at R7 and R15.
Redundant Outputs
Remove R20 and/or C4.
Single Ended Input
Install R11 (0Ω).
Gain = +2
Remove R7.
AC-Coupled
Install 220µF at C3.
Redundant Outputs
CASCADED AMPLIFIERS, GAIN = +4
Remove R16, R7, R12.
Single Ended Input
Install R10 (0Ω).
Gain = +4
AC-Coupled
Move R17, R18 resistors to R2, R3.
Single Output at J3
Install R8, R14 (0Ω).
Change R9 to 20Ω (for gain flatness).
Install 220µF at C3.
These two voltage compliance restrictions are easy to
meet on a single +5V or split ±5V supply by tying DGND
to the ground plane, which by default is done on the
demo board. However, if using split supplies and
VCC<3V, then the first requirement will not be met, and
4
DEMO CIRCUIT DC1108 QUICK START GUIDE
650MHZ DIFF. ADC DRIVER / DUAL SELECTABLE-GAIN AMPLIFIER
5
Similar pages