Linear Technology DC1464A Manuel utilisateur

DEMO CIRCUIT DC1464 QUICK START GUIDE FOR LTC6412

DESCRIPTION

Demonstration circuit 1464 features the LTC6412 ana-

log-controlled VGA. The demo board incorporates a va-

riety of passive components to allow for direct connec-

tion 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 –V

control mode in the power-on and amplifier-

enabled state (

SHDN

=1,

=0).

The demo board is easily configured to access the +V

control mode and

SHDN

features. Other simple PCB

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.

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:

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.

Apply +3.3V between +V

and GND turrets. Limit

supply current to approximately 150mA.

Apply the desired control signal to either the –V

turret or the –V

SMA to access the –V

pin of the

LTC6412. For this –V

control mode, an

increase

control signal voltage produces a

decrease

in ampli-

fier gain.

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 con-

trol signal voltage before turning down the supply volt-

age. This proper sequence will prevent excessive current

through the ESD diodes from the ±V

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 evalua-

tion configuration. Other connectors provide flexibility

for fast control signals, differential input/output signals,

and balun loss calibration.

DEMO CIRCUI

146

QUICK START GUID

LTC641

800MHz, 31dB Rang

Analog-Controlled VG

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DEMO CIRCUIT DC1464 QUICK START GUIDE FOR LTC6412

Table 1. DC1464 SMA Connector Descriptions

Figure 1.

Picture of DC1464 Top Silkscreen with recommended

default measurement setup connections shown in maroon.

CONNECTOR FUNCTION

J1 (+IN) Differential input connected to input balun for single-ended operation.

Drive from a 50 Ohm signal source. No external termination needed.

J2 (+OUT) 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.

J3 (-IN) Differential input

. Not connected by default

. Resistor R9 can be removed to drive the input balun differentially.

J4 (-OUT) Differential output.

Not connected by default

. Capacitor at C21 can be moved to C9 to drive the differential outputs.

J5 (VGAIN) SMA terminal.

Default connected in parallel with –VG turret to the –VG pin of LTC6412

. Used to apply fast control

signals. Move jumper R15 to location R14 and jumper R19 to location R18 to configure for +V

control.

J6 (TEST IN)

J7 (TEST OUT) Cascaded 1:1 balun thru connection. Used to estimate the loss of the input balun at the frequency of interest.

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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

=1,

=0). The

SHDN

pin is pulled high with a 1kΩ resistor to V

, and

the

pin is pulled low with a 1kΩ resistor to ground.

One can override these board-level defaults by applying

voltages directly to the

SHDN

and

turrets as needed.

–V

AND +V

CONTROL

The factory default configuration is set for –V

control

with the V

GAIN

SMA connector hooked in parallel with the

–V

turret. These control inputs can be reconfigured for

operation by moving jumper R15 to location R14

and moving jumper R19 to location R18. Clip leads to

the ±V

turrets are susceptible to noise pickup and

should be lowpass filtered to avoid AM up-conversion

artifacts. While using the ±V

turrets, a 4.7µF capacitor

from the V

GAIN

SMA terminal to ground provides an ef-

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 dif-

ferential input drive (50 Ohm).

Alternatively, the input balun T1 can be removed com-

pletely and the ±IN signals routed directly to C5 and C8

using 0603 0Ω jumpers across the input balun pads.

DIFFERENTIAL OUTPUTS

The output connectors can be configured for differential

drive. Move capacitor C21 to location C9 to enable dif-

ferential output drive (50 Ohm).

Alternatively, the output balun can be removed com-

pletely with the ±OUT signals routed to LTC6412 output

pins using 0Ω 0603 jumpers across the output balun

pads as shown below. This transformerless configura-

tion 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 recom-

mended. 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

Turrets to V

, 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

Figure 2.

DC1464A Schematic

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DEMO CIRCUIT DC1464 QUICK START GUIDE FOR LTC6412

Table 2. DC1464A Parts List

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Table des matières

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