TPS7A1108PDRVT - TEXAS INSTRUMENTS

DEMO CIRCUIT DC1103 QUICK START GUIDE

LOW NOISE, LOW DISTORTION DIFFERENTIAL IF AMPLIFIER

DESCRIPTION

Demonstration circuit 1103 features the LTC6410-6 low

noise, low distortion differential Intermediate Frequency (IF)

Amplifier. It incorporates a variety of passive components

to support configurations for varied applications. Single-

ended or differential input and output configurations are

possible, and there is a test/calibration circuit to null out the

effects of on-board circuit components.

The LTC6410-6 is a high-speed differential amplifier with

6dB of voltage gain and superior distortion and noise per-

formance, perfect for demanding communications tran-

sceivers, cellular base-stations, and other high-speed signal

chain applications. The LTC6410-6 features a fully differen-

tial input and output and is capable of

directly

driving a 50Ω

load

. One standout feature of the LTC6410-6 is the ability to

independently adjust the input impedance with two resistors

at the inputs. This allows the user to easily enhance the

noise figure and power gain of the system for optimal per-

formance.

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:

Connect the power supply as shown. The LTC6410-6

accepts supply voltages from 2.8-5.5V. The power la-

bels of VCC,

SHDN

, and GND directly correspond to

the V+,

SHDN

, and V- pins of the LTC6410-6, respec-

tively. Jumper JP1 shuts down the LTC6410-6.

For network analyzer use, the user can calibrate out

board and transformer effects using J6 and J7.

Apply an input signal to J2. A low-distortion, low noise

signal source with an external high-order filter will yield

the best performance (this does not apply to network

analysis). DC1103’s input is impedance-matched to

by default; no external termination is necessary.

Observe the output via J5. The output is capable of

driving a 50

load, such as the input of a network or

spectrum analyzer. By default, the output is imped-

ance-matched to 50

Table 1: DC1103 Connector Descriptions

CONNECTOR FUNCTION

J1 (-IN) Differential Input. Not connected by default. Capacitor

R6 can installed and R2 removed to drive the DC1103

differentially.

J2 (+IN) Differential Input. Use this connector to supply an input

to the DC1103. Drive from a 50Ω signal source, no ex-

ternal termination necessary.

TP4 (VBIAS) Self-Bias Voltage Adjust. By default, 1.45V is supplied

to this pin by two resistors (VCC=3V). Override this

voltage with any low-impedance DC voltage source.

J4 (-OUT) Differential Output. Not connected by default. Capaci-

tor R12 can be installed and R14 removed for differen-

tial output drive.

J5 (+OUT)

Output. Impedance-matched to 50

, can be used to

drive a 50Ω network/spectrum analyzer input.

J6 (TEST IN) Calibration network input. Use with a network analyzer

to calibrate out effects of board trace parasitics, trans-

formers, and SMA connectors.

J7 (TEST OUT) Calibration network output.

DEMO CIRCUIT 110

QUICK START GUIDE

LTC6410-

Differential IF Amplifie

DEMO CIRCUIT DC1103 QUICK START GUIDE

LOW NOISE, LOW DISTORTION DIFFERENTIAL IF AMPLIFIER

ADDITIONAL INFORMATION

Although the DC1103 demo board is ready to use out of the

box, it has features that you can access by adding, remov-

ing or changing components on the board. This and other

important board information are included in this section.

DIFFERENTIAL INPUTS

To drive the inputs differentially, remove capacitor C31 and

install C26. J1 and J2 can now be driven differentially from

a 50Ω signal source. The input to the DC1103 will still be

matched to 50Ω (differential) when driven in this manner.

SMA CONNECTOR SPACING

The input SMA connectors are spaced 0.6” (15.24mm)

apart, suitable for direct connection to the DC1119 demo

board for Linear Technology’s LT5527, LT5557, and

LT5559 high linearity downconverting mixers.

The output SMA connectors are spaced 0.8” (20.32mm)

apart, suitable for direct connection to various Linear Tech-

nology amplifier/ADC-driver demo boards such as DC800

(LT1993) and DC987 (LTC6400, LTC6401).

ADJUSTING THE INPUT IMPEDANCE

The input impedance of the LTC6410 can be adjusted in the

range of 58Ω-2000Ω by replacing R5 and R6 with equal-

value non-zero resistors. The correct resistor value for the

desired

differential

input impedance is:

(

)

DIFF

DIFF Z

RR −

−⋅

=2000 2200003810

,65

Adjusting the input impedance too high may affect the

performance of the part. See the LTC6410 datasheet.

Proper Measurement Equipment Setup

DEMO CIRCUIT DC1103 QUICK START GUIDE

LOW NOISE, LOW DISTORTION DIFFERENTIAL IF AMPLIFIER

DC COUPLING THE INPUTS/OUTPUTS

It is possible to DC couple the LTC6410 in the signal chain.

Capacitors C26, C32 and C3-C4 should be replaced with 0Ω

resistors. Additionally, C30 and C31 should be removed. As

a warning, the input impedance of the LTC6410-6 can cause

large input bias currents if DC1103 is DC-coupled at the

inputs. Additionally, the inputs must be DC-biased to within

the common-mode range of the LTC6410.

If transformers T1 and T2 are transmission-line transfor-

mers (the transformers included on-board are TLTs), DC

voltages and currents will propagate through at the input

and output unless AC-coupling capacitors are installed.

When DC coupling the inputs, it may also be desirable to DC

couple the TERM inputs of the LTC6410 to the signal in-

puts. To do this, replace C1 and C2 with 0Ω

resistors. This

will achieve a wideband (down to DC frequency) imped-

ance match at the input, at the expense of increased

common-mode output offset. See the LTC6410 datasheet

for details.

The outputs of the LTC6410 will self-bias to the voltage at

the V

OCM

pin. If DC-coupled, the load to ground at each

output should be considered so that excessive current is

not drawn from the outputs. A differential R

LOAD

should be

installed at R15 instead to avoid large quiescent load cur-

rents. On the demo board, capacitor C30 should be re-

moved for this reason if DC coupling at the output.

DIFFERENTIAL OUTPUTS

To use the both outputs of the DC1103, remove capacitor

C30 and install C3. The output now appears differentially

across J4 and J5. The output of the DC1103 will still be

matched to 50Ω (differentially) when used in this manner.

See the LTC6410 datasheet for more details.

CHANGING THE BIAS VOLTAGE

Turret TP4 controls the self-bias voltage of DC1103. This

function can be used to bias the next stage for optimum

system performance. If used for this purpose, AC-coupling

capacitors C3 and C4 can be shorted or replaced by 0Ω

resistors to allow the DC bias to reach the output. By de-

fault, internal resistors supply 1.45V to the V

BIAS

pin (with

V+=3.0V). This voltage can be over-ridden with an external

voltage source at TP4 and/or by installing resistors R19 and

R20.

OUTPUT DRIVE

The output of the LTC6410-6 is designed to directly drive

impedances as low as 50Ω

. This makes the part suitable

for insertion into 50

signal chains without special con-

siderations of amplifier loading and impedance matching.

SHUTDOWN

Jumper JP1 and TP1 control the shutdown function of

DC1103. When set to the EN position, the part will be on

and draw quiescent current. In the DIS position, the part will

be in shutdown and draw a very small amount of quiescent

current. Remove the JP1 shunt to drive TP1 directly with a

voltage source.

NOTE.

The V

OCM

bias resistors R19 and R20 draw current

from VCC to GND, and must be accounted for when

measuring the current of the LTC6410-6 (especially in

shutdown). By default, these resistors are not installed on

the board.

CABLES AND CONNECTORS

Long BNC or SMA cables are transmission lines, and for

best circuit performance should be kept as short as possi-

ble. BNC/SMA cables or barrels should be characterized (or

nulled out through calibration) for good high-frequency per-

formance.

SCHEMATIC NOTES

The calibration circuit, as shown in the schematic, contains

two extra resistors R21-R22. These resistors are included

for added circuit flexibility, and are not typically populated.

Additionally, R15, C11, and C16 are included for possible

output resistive load or filtering, and are also unpopulated.

DEMO CIRCUIT DC1103 QUICK START GUIDE

LOW NOISE, LOW DISTORTION DIFFERENTIAL IF AMPLIFIER