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DEMO CIRCUI
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DEMO CIRCUIT DC1464 QUICK START GUIDE FOR LTC6412
QUICK START GUID
LTC641
800MHz, 31dB Rang
Analog-Controlled VG
DESCRIPTION
Demonstration circuit 1464 features the LTC6412 analog-controlled VGA. The demo board incorporates a variety of passive components to allow for direct connection to a 2-port network analyzer or other single-ended
50Ω test system for simplified evaluation.
The 1464 demo board factory default configuration is set
for –VG control mode in the power-on and amplifierenabled state (
SHDN
=1, EN=0).
The demo board is easily configured to access the +VG
control mode and EN/
modifications can accommodate differential input/output
signals and shunt tuning elements for bread-boarding
into larger systems.
Design files for this circuit board are available. Call
the LTC factory.
L, LTC, LTM, and LT are trademarks of Linear Technology Corporation. Other product
names may be trademarks of the companies that manufacture the products.
SHDN
features. Other simple PCB
QUICK START PROCEDURE
Demonstration circuit 1464 is easy to set up to evaluate
the performance of the LTC6412. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
1. Connect SMA cables to the +IN and +OUT ports.
Applied signal should be less than +10dBm peak RF
power to avoid damage in the power-off state.
2. Apply +3.3V between +VCC and GND turrets. Limit
supply current to approximately 150mA.
3. Apply the desired control signal to either the –VG
turret or the –VG SMA to access the –VG pin of the
LTC6412. For this –VG control mode, an
control signal voltage produces a
fier gain.
decrease
increase
in ampli-
in
This procedure contains only one critical sequence order.
The user must apply supply voltage before applying the
control signal voltage and remove or turn-down the control signal voltage before turning down the supply voltage. This proper sequence will prevent excessive current
through the ESD diodes from the ±VG pins to the positive
supply, V
Table 1 shows the function of each SMA connector on
the board. Only J1 and J2 are used in the default evaluation configuration. Other connectors provide flexibility
for fast control signals, differential input/output signals,
and balun loss calibration.
CC
.
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DEMO CIRCUIT DC1464 QUICK START GUIDE FOR LTC6412
Table 1. DC1464 SMA Connector Descriptions
CONNECTOR FUNCTION
J1 (+IN)
J2 (+OUT)
J3 (-IN) Differential input
J4 (-OUT) Differential output.
J5 (VGAIN)
J6 (TEST IN)
J7 (TEST OUT)
Differential input connected to input balun for single-ended operation.
Drive from a 50 Ohm signal source. No external termination needed.
Differential output connected to output balun for single-ended operation.
Impedance matched to 50 Ohms for direct connection to a 50 Ohm network/spectrum analyzer input.
SMA terminal.
signals. Move jumper R15 to location R14 and jumper R19 to location R18 to configure for +V
Cascaded 1:1 balun thru connection. Used to estimate the loss of the input balun at the frequency of interest.
Default connected in parallel with –VG turret to the –VG pin of LTC6412
. Not connected by default
Not connected by default
. Resistor R9 can be removed to drive the input balun differentially.
. Capacitor at C21 can be moved to C9 to drive the differential outputs.
. Used to apply fast control
control.
G
Figure 1. Picture of DC1464 Top Silkscreen with recommended
default measurement setup connections shown in maroon.
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DEMO CIRCUIT DC1464 QUICK START GUIDE FOR LTC6412
ADDITIONAL INFORMATION
SHUTDOWN AND ENABLE
The factory default configuration is set for the power-on
and amplifier-enabled state (
SHDN
pin is pulled high with a 1kΩ resistor to VCC, and
the EN pin is pulled low with a 1kΩ resistor to ground.
One can override these board-level defaults by applying
voltages directly to the
–VG AND +VG CONTROL
The factory default configuration is set for –VG control
with the V
–VG turret. These control inputs can be reconfigured for
+VG operation by moving jumper R15 to location R14
and moving jumper R19 to location R18. Clip leads to
the ±VG turrets are susceptible to noise pickup and
should be lowpass filtered to avoid AM up-conversion
artifacts. While using the ±VG turrets, a 4.7µF capacitor
from the V
fective lowpass filter with a cutoff frequency of 340 Hz.
DIFFERENTIAL INPUTS
The inputs connectors can be configured for differential
drive. Remove the jumper in location R9 to enable differential input drive (50 Ohm).
Alternatively, the input balun T1 can be removed completely and the ±IN signals routed directly to C5 and C8
using 0603 0Ω jumpers across the input balun pads.
SMA connector hooked in parallel with the
GAIN
SMA terminal to ground provides an ef-
GAIN
SHDN
SHDN
=1, EN=0). The
and EN turrets as needed.
DIFFERENTIAL OUTPUTS
The output connectors can be configured for differential
drive. Move capacitor C21 to location C9 to enable differential output drive (50 Ohm).
Alternatively, the output balun can be removed completely with the ±OUT signals routed to LTC6412 output
pins using 0Ω 0603 jumpers across the output balun
pads as shown below. This transformerless configuration requires two additional inductors from the balun
center tap pad to conduct supply current to the LTC6412
output pins. The inductors should choke the RF signal
sufficiently at the frequency of interest while passing DC
current with minimal supply drop, <100mV is recommended. A surface mount 0603 inductor is a good size
choice to bridge the PCB pad gap. Keep the DC blocking
capacitors at C6 and C9 to avoid a DC path to the output
SMA connectors.
TURRET OPTIONS
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Turrets to VCM, DECL_1, and DECL_2 are usually not
stuffed as they represent internal voltages generated by
LTC6412. Do not connect to these nodes beyond the
recommended bypass capacitors to ground.
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DEMO CIRCUIT DC1464 QUICK START GUIDE FOR LTC6412
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Figure 2. DC1464A Schematic
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DEMO CIRCUIT DC1464 QUICK START GUIDE FOR LTC6412
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Table 2. DC1464A Parts List
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Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
Analog Devices Inc.:
DC1464A
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