DC1398A-GA - LINEAR TECHNOLOGY

DC1250

DESCRIPTION

Demonstration circuit 1398 is an evaluation board featur-

ing Linear Technology Corporation’s LTM9001 16-bit

Receiver Subsystem. DC1398 demonstrates good circuit

layout techniques and recommended external circuitry

for optimal system performance.

DC1398 comes with Linear Technology’s 16-bit

LTM9001 amplifier/ADC subsystem installed. The board

includes a wideband input transformer (for evaluation

with a single-ended RF signal generator) and output

CMOS buffers.

DC1398 plugs into the DC890 Data Ac-

quisition demo board and the output can be easily ana-

lyzed with Linear Technology’s PScope data processing

software, which is available for no charge 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 LTM9001 is simple

with DC1398, and requires only an input source, a clock

source, a computer, and a lab power supply. Refer to

Figure 1 for proper board evaluation equipment setup

and follow the procedure below:

Connect the power supply as shown in Figure 1.

There are on-board low-noise voltage regulators that

provide the three supply voltages for the LTM9001.

The entire board and all components share a com-

mon ground. The power supply should still be a low-

noise lab power supply capable of supplying at least

1 Amp.

Provide an encode clock to the ADC via SMA con-

nector J3. Use a low-phase-noise clock source such

as a filtered RF signal generator or a high-quality

clock oscillator.

Obtain DC1216 for a low-phase-

noise ADC clock source that can plug directly into

DC1398.

NOTE.

Similar to having a noisy input, a high-jitter (phase noise)

encode clock will degrade the signal-to-noise ratio (SNR) of the

system.

Table 1: DC1398 Connectors and Jumpers

REFERENCE FUNCTION

J1 (AIN-) Differential Board Input.

Normally not con-

nected.

See text for differential

input evalu

tion methods.

J2 (AIN+) Board Signal Input. Impedance-matched to

Ω

for use with lab signal generators.

J3 (ENC) Board Clock Input. Impedance-matched to

Ω.

Drive with a low-phase-noise clock oscil-

lator or filtered sine wave signal source.

E1 (EXT REF) Reference input to adjust the full-scale range of

the LTM9001. Connects to the SENSE pin; by

default, tied to VDD for internal reference.

E2 (VS) DC Supply input (3.8 to 6VDC).

E3 (GND) DC ground.

JP1 (PGA_GAIN) Selects the input range of LTM9001. Default is

LOW (low PGA gain, larger input range)

JP2 (RAND) Output Randomizer. Default is NORM.

JP3 (ADC_SHDN) Enables the LTM9001 ADC. Default is NORM.

JP4 (DITH) ADC Internal Dither. Default is OFF.

JP5 (AMP_EN) Enables the LTM9001 amplifier. Default is EN.

Apply an input signal to the board. DC1398 allows

great flexibility in applying input signals (see the sec-

tion on Applying Input Signals). For best results, use a

low distortion, low noise signal generator with suffi-

cient filtering to avoid degrading the performance of

the amplifier and ADC.

Observe the ADC output with demo circuit DC890, a

USB cable, a Windows computer, and Linear Tech-

nology’s Pscope data processing software.

DEMO CIRCUIT 1398

QUICK START GUIDE

LTM9001 16-

bit High

Per

formance ADC Drivers

LTM9001

Figure 1.

Proper Evaluation Equipment Setup

ADDITIONAL INFORMATION

Although the DC1398 demo board is ready to use on de-

livery, it has additional flexibility built in for various types

of input networks. Below is some information about con-

figuring DC1398 to meet the specific needs of your eval-

uation.

APPLYING INPUT SIGNALS

The input network consists of various components de-

signed to allow either single-ended or differential inputs,

AC-coupled or DC-coupled. Table 2 shows some possi-

ble input configurations, and which components to in-

stall. LTM9001 is designed for excellent performance

with both single-ended and differential input drive, with

little difference in distortion performance. When using

DC-coupled inputs, the inputs to DC1398 need to be lev-

el-shifted to within the input common-mode limits in the

datasheet.

Table 2: DC1398 Input Configuration Guide

CONFIGURATION COMPONENTS NECESSARY

Single-Ended Input

AC-Coupled

(Default Setup)

No change. Transformer T1 acts as a balun for

differential drive.

Single-Ended Input

No Transformer

AC-Coupled

Remove T1, replace with 0

Ω

jumpers. May need

to install impedance-matching resistor at R4

or R2/R6.

Single-Ended Input

No Transformer

DC-Coupled

Same as above. Change C1 and C8 to 0

Ω

jump-

ers. Inputs must be within the common-

mode voltage limits of LTM9001.

Differential Inputs Remove R7 and install R5. T1 and C1/C8 can be

replaced with 0

Ω

for DC coupling.

Signal

Generator

HP 8644B

or equiv.

Power Supply

(3.8V-6V @ 1.0A)

To DC890

BPF

NOTE.

Even a high

ality signal

synthesizer will still have noise and

harmonics that should be attenuated

with a low-pass or band-pass filter.

For good-quality high order filters,

see TTE, Lark Engineering, or

equivalent.

BPF

RF Signal Ge

erator

(HP 8644B) or other

low phase noise

clock source (e.g. DC1216)

LTM9001

NOTE.

When driving the ADC driver with a direct DC-coupled path, increased

input bias currents may occur due to the amplifier’s input impedance. See

the LTM9001 datasheet for more details.

OTHER BOARD CIRCUITRY

Device U5 is an EEPROM device that is used by the

PScope software to identify the board and apply the cor-

rect settings for the data collection.

USING PSCOPE SOFTWARE

PScope, downloadable from Linear Technology’s website

http://www.linear.com/, processes data from the DC890

FastDAACS board and displays FFT and signal analysis

information on the computer screen.

The on-board EEPROM U5 should enable automatic

board detection and auto-configuration of the software,

but if the user wishes to change the settings, they can

easily do so.

From the Configure menu in the toolbar, uncheck “Auto-

detect Device”. The default settings for DC1398 are

shown in Figure 2. The LTM9001 also has an output ran-

domizer, which the user needs to select if it is enabled on

the board. The software will automatically un-randomize

the output by performing an exclusive-OR with each bit

and the LSB.

Figure 2. Entering the correct device information for your ADC. Select the correct parameters for the DC1398. Under normal conditions,

PSCOPE should automatically recognize the board and adjust the software settings accordingly.

LTM9001

Figure 3. Schematic