Linear Technology LT6411 Manuel utilisateur

LT6411 AND LTC2249 A

DESCRIPTION

Demonstration circuit 1057 is a reference design

featuring Linear Technology Corporation’s LT6411

High Speed Amplifier/ADC Driver with an on-board

LTC2249 14-bit, 80MSPS ADC. DC1057 demon-

strates good circuit layout techniques and recom-

mended component selection for optimal system

performance. The ADC driver input and output

networks are flexible, allowing for AC or DC cou-

pling, gains of 0dB or 6dB, single-ended or differ-

ential configurations, and signal low-pass or band-

pass filtering before the ADC.

DC1057 also allows the flexibility of selecting the

CMOS output supply voltage. DC1057 includes an

on-board 40-pin edge connector for use with the

DC718 Data Acquisition demo board and Linear

Technology’s QuickEval-II data processing soft-

ware, available on our website at

http://www.linear.com.

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

Validating the performance of the LT6411 ADC

Driver-ADC combination is simple with DC1057,

and requires only two signal generators and some

basic lab equipment. Table 1 shows the function of

each I/O connector and selectable jumper on the

board. Refer to Figure 1 for proper board evalua-

tion equipment setup and follow the procedure be-

low:

Connect the power supplies as shown. The

power supply connector labeled VCC powers

the ADC driver. VDD powers the ADC, and

OVDD provides power to both the ADC output

stage and the two CMOS output buffers. The

entire board and all components share common

ground planes. Check the supply voltages be-

fore applying power, to avoid damage from over-

voltage conditions.

Provide an encode clock to the ADC via SMA

connector J4. For best performance, a high-

quality sine wave synthesizer with an external

band-pass filter will provide a stable, low-phase-

noise clock source. A crystal oscillator will also

provide good performance. DC1057 includes an

on-board clock amplifier/buffer IC to provide a

large-amplitude clock source to the ADC.

NOTE.

A poor quality encode clock can significantly degrade the

signal-to-noise ratio (SNR) of the driver-ADC combination.

Table 1: DC1057 Connectors and Descriptions

REFERENCE FUNCTION

J1 (AIN+) Analog Input (50

Ω

termination imped-

ance)

J2 (AIN-) Analog Input (by default, tied to ground

via resistor R16 for single-ended-to-

differential conversion)

J3 (40-pin conn) Provides direct connection to DC718.

CMOS Output Buffers provide parallel

data output and clock signals (see sche-

matic)

J4 (Encode

Clock)

ADC Encode Clock. For best perform-

ance, use a high-quality low-jitter clock

source.

JP1 (ENABLE) Enable/Disable LT6411. Default is EN.

Apply an input signal to the board. DC1057 al-

lows great flexibility in applying input signals

(see the section on Applying Input Signals). For

best results, use a low distortion, low noise sig-

nal generator with high order low-pass or band-

DEMO CIRCUIT 1057

QUICK START GUIDE

LT6411 High-

Speed

ADC Driver Combo

Board

LT6411 AND LTC2249 A

pass filtering to avoid degrading the perform-

ance of the ADC driver and ADC.

Observe the ADC output with demo circuit

DC718, a USB cable, a Windows computer, and

Linear Technology’s QuickEval-II data process-

ing software. See Figure 2 for the general board

evaluation setup diagram.

NOTE.

See the DC718 Quick Start Guide for instructions on using

the DC718 QuickDAACS data acquisition demo board.

Figure 1. Proper Evaluation Equipment Setup

Figure 2. Evaluation Setup with DC718, Computer, and QuickEval-II Software

Signal

Generator

HP 8644B

or equiv

Signal Generator

HP 8644B or equiv

Amplifier Power Supply

ADC Power Supply

Power Supply

CMOS Output

To DC718

BPF

DC718

QuickDAACS

Data Acquisition

Board

Input Signal Generator

with LPF, BPF

Windows PC

w/ QuickEval-II

Processing

Software

USB

NOTE.

Even a high-quality signal

synthesizer will still have noise

and harmonics that could be

attenuated with a low-pass or

band-pass filter. For good-quality

high order filters, see TTE, Lark

Engineering, or equivalent.

BPF

LT6411 HIGH-SPEED ADC DRIVER COMBO BOARD

Figure 3. DC1057 Input Network, see Table 2 and text for configuration options

ADDITIONAL INFORMATION

Although the DC1057 demo board is ready to use,

it has additional flexibility built in for various types

of input networks, filtering configurations, and sin-

gle-ended or differential inputs. Below is some in-

formation about configuring DC1057 to meet the

specific needs of any application.

APPLYING INPUT SIGNALS

The input network consists of various components

designed to allow either single-ended or differential

inputs, transformer-coupled or DC-coupled. Table

2 and Figure 4 show some possible input configu-

rations, and which components to install. Linear

Technology’s ADC driver families are generally

characterized and designed for both single-ended

and differential input drive, but for optimal per-

formance differential input drive (or transformer-

coupled drive) is recommended. By default, trans-

former drive is used on DC1057 so that only a sin-

gle-ended input is needed. See the LT6411 data-

sheet for more comprehensive information on pos-

sible configurations.

Table 2: DC1057 Input Configuration Guide

CONFIGURATION COMPONENTS NECESSARY

Single-Ended In-

put

Transformer Drive

Gain = +2

(default, not

shown)

Install 0

Ω

jumper at R16 or R6.

Install transformer T1. Install 25

Ω

at R7

and R13 for impedance matching.

Establish DC bias by using R37 and R38

or R2/R3 and R17/R18.

Tie feedback resistors to AC ground

through 0.1µF at C5 and C9 (or replace

with 0

Ω

resistors if using dual sup-

plies).

Single-Ended In-

put

Single-Ended

Drive

Gain = +2

(Figure 4a)

Install 0

Ω

jumper at R16. Install R6 for

impedance matching.

Remove T1, C5, C9. Install

0Ω

at R5, R10,

R39, R42.

Install 0.1µF at C33, C34. Establish DC

bias with R17, R18 resistors.

Install 0

Ω

at R5, R10.

LT6411 HIGH-SPEED ADC DRIVER COMBO BOARD

Differential Input

AC-Coupled

Gain = +2

(Figure 4b)

Remove R16 and R6. Install 0

Ω

at R39,

R42.

Remove T1. Install 0.1µF at C33, C34.

Install R7 and R13 for impedance match-

ing.

Establish DC bias by using R37 and R38

or R2/R3 and R17/R18.

Tie feedback resistors to AC ground

through 0.1µF at C5 and C9 (or replace

with 0

Ω

resistors if using dual sup-

plies).

Differential Input

AC-Coupled

Gain = +1

(Figure 4c)

Remove R16 and R6. Install 0

Ω

at R39,

R42.

Remove T1. Install 0.1µF at C33, C34.

Install R7 and R13 for impedance match-

ing.

Establish DC bias by using R37 and R38

or R2/R3 and R17/R18.

Install 0

Ω

at R5, R14 to establish gain of

+1.

Differential Input

AC-Coupled

Gain = -1

(Figure 4d)

Remove R16 and R6.

Remove T1. Install 0.1µF at C33, C34.

Install R7 or R13 for impedance matching.

Establish DC bias by using R2/R3 and

R17/R18.

Install 0

Ω

at R40, R41 to establish gain of -

Differential Input

AC-Coupled

Gain = +3

(Figure 4e)

Remove R16 and R6

Remove T1. Install 0.1µF at C33, C34.

Install R7 or R13 for impedance matching.

Establish DC bias by using R37 and R38

or R2/R3 and R17/R18.

Install 0

Ω

jumpers in the positions shown

in Figure 4e, to establish gain of +3.

Differential Input

DC-Coupled*

(Figure 4f)

Remove R16 and R6.

Remove T1. Install 0

Ω

at R39, R42.

Install R7 or R13 for impedance matching.

Remove CIN+ and CIN-, replace with 0

Ω

Install 0

Ω

jumpers at C5, C9.

NOTE.

* When driving the ADC driver with a direct DC-coupled

path, be aware of the increased input currents that may occur due to

the output common-mode voltage and internal resistor networks.

The DC common-mode voltage requirements of

Linear Technology’s ADC drivers do not always

extend to ground (the negative supply voltage).

When replacing CIN+ and CIN- with

0Ω

jumpers,

make sure to level-shift the inputs so that the ADC

driver’s input common-mode voltage requirement

is met.

Recommended 1:1 transformers for populating T1

are M-A/Com’s ETC1-1-13 and ETC1-1T.

POWER SUPPLY BYPASS CAPACITANCE

Depending on the quality of the power supplies

provided to DC1057, it may be desirable to add

larger bulk capacitors at C1, C29, C30, and C31.

This will not be necessary with clean, low-

impedance power supplies.

FILTER NETWORKS

For narrowband input signals, L1 and C6 are in-

cluded at the output of the ADC driver for easy

band-pass filter design. In addition, there are extra

pads for resistors, capacitors, and other filter net-

work components at the output of the LT6411.

CHANGING THE ADC DRIVER’S OUTPUT

COMMON-MODE VOLTAGE

The output common-mode voltage of the ADC

driver must be set either at the input of the LT6411

(see Table 2), or by AC coupling the output of the

LT6411. R24 and R25 are optional resistors con-

nected to the VCM output of the ADC that can be

installed to apply the proper common-mode volt-

age to the ADC inputs.

QUICKDAACS CIRCUITRY

Logic gate U6, installed on the back of DC1057,

enables the CMOS output buffers when DC1057 is

plugged into DC718, which pulls its input high. De-

vice U5 is an EEPROM device that is used by the

QuickEval software, and does not affect board op-

eration or performance.

USING QUICKEVAL-II SOFTWARE

QuickEval-II, downloadable from Linear Technol-

ogy’s website http://www.linear.com/, processes

data from the DC718 QuickDAACS board and dis-

plays FFT and signal analysis information on the

computer screen. This section describes how to

use the software to view the output from DC1057.

The first step is to select the correct input board.

See Figure 5 From the Configure menu in the

LT6411 HIGH-SPEED ADC DRIVER COMBO BOARD

toolbar, select DC718 (QuickDAACs). The next

step is to use the proper settings for the DC1057

output. See Figure 6 Select the correct device from

the menu bar, and select the “Randomized” option

if the output randomizer is turned on (via JP4). Af-

ter configuration is through, the program should be

ready to collect and display data. See the Help file

for instructions on general software use.

LT6411 HIGH-SPEED ADC DRIVER COMBO BOARD

Figure 4. Pictures of DC1057 input network configurations. Blocks show where components should be mounted, ac-

cording to Table 2.

A B

C D

E F

LT6411 HIGH-SPEED ADC DRIVER COMBO BOARD

Figure 5. Selecting the correct input to QuickEval-II

Figure 6. Entering the correct device information for your ADC. Select the correct device for your board.

LT6411 HIGH-SPEED ADC DRIVER COMBO BOARD

Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Analog Devices Inc.:

DC1057A

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