DC782A-W - LINEAR TECHNOLOGY

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 782

10/12/14 BIT 10 TO 125 MSPS ADC

LTC2236, LTC2237, LTC2238, LTC2239, LTC2225, LTC2226,

LTC2227, LTC2228, LTC2229, LTC2245, LTC2246, LTC2247,

LTC2248, LTC2249 LTC2250, LTC2251, LTC2252, LTC2253,

LTC2254, or LTC2255

DESCRIPTION

Demonstration circuit 782 supports a family of

10/12/14 BIT 10 TO 125 MSPS ADCs. Each as-

sembly features one of the following devices:

LTC2236, LTC2237, LTC2238, LTC2239, LTC2225,

LTC2226, LTC2227, LTC2228, LTC2229, LTC2245,

LTC2246, LTC2247, LTC2248, LTC2249, LTC2250,

LTC2251 LTC2253, LTC2254, or LTC2255 high

speed, high dynamic range ADCs.

Several versions of the 782A demo board support-

ing the 10 BIT, 12 BIT and 14 BIT series of A/D con-

verters across the 10 to 125 MSPS speed/power

range are listed in Table 1.

Depending on the required resolution, sample rate

and input frequency, the DC782 is supplied with the

appropriate A/D and with an optimized input circuit

The circuitry on the analog inputs is optimized for

analog input frequencies below 70 MHz or between

70 MHz to 170 MHz (Please read ANALOG INPUT

NETWORK SECTION). For Higher operating fre-

quencies, contact the factory for support.

Design files for this circuit board are available.

Call the LTC factory.

LTC is a trademark of Linear Technology Corporation

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 782

10/12/14 BIT 10 TO 125 MSPS ADC

Table 1.

DC782A Variants

DC782 VARIANTS ADC PART NUMBER RESOLUTION* MAXIMUM SAMPLE

RATE

INPUT FREQUENCY

782A-A LTC2249 14-Bit 80Msps 1MHz < A

< 70MHz

782A-B LTC2248 14-Bit 65Msps 1MHz < A

< 70MHz

782A-C LTC2247 14-Bit 40Msps 1MHz < A

< 70MHz

782A-D LTC2246 14-Bit 25Msps 1MHz < A

< 70MHz

782A-E LTC2245 14-Bit 10Msps 1MHz < A

< 70MHz

782A-F LTC2229 12-Bit 80Msps 1MHz < A

< 70MHz

782A-G LTC2228 12-Bit 65Msps 1MHz < A

< 70MHz

782A-H LTC2227 12-Bit 40Msps 1MHz < A

< 70MHz

782A-J LTC2226 12-Bit 25Msps 1MHz < A

< 70MHz

782A-K LTC2225 12-Bit 10Msps 1MHz < A

< 70MHz

782A-L LTC2239 10-Bit 80Msps 1MHz < A

< 70MHz

782A-M LTC2238 10-Bit 65Msps 1MHz < A

< 70MHz

782A-N LTC2237 10-Bit 40Msps 1MHz < A

< 70MHz

782A-P LTC2236 10-Bit 25Msps 1MHz < A

< 70MHz

782A-Q LTC2249 14-Bit 80Msps 70MHz <A

< 170MHz

782A-R LTC2248 14-Bit 65Msps 70MHz <A

< 170MHz

782A-S LTC2255 14-Bit 125 Msps 10MHz <A

< 170MHz

782A-T LTC2254 14-Bit 105 Msps 10MHz <A

< 170MHz

782A-U LTC2253 12-Bit 125 Msps 10MHz <A

< 170MHz

782A-V LTC2252 12-Bit 105 Msps 10MHz <A

< 170MHz

782A-W LTC2251 10-Bit 125 Msps 10MHz <A

< 170MHz

782A-X LTC2250 10-Bit 105 Msps 10MHz <A

< 170MHz

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 782

10/12/14 BIT 10 TO 125 MSPS ADC

Table 2.

Performance Summary (TA = 25°C)

PARAMETER CONDITION VALUE

Supply Voltage Depending on sampling rate and the A/D converter provided,

this supply must provide up to 150mA.

Optimized for 3.0V

[2.7V 3.6V min/max]

Analog input range Depending on Sense Pin Voltage 1V

to 2V

Minimum Logic High 2.4V

Logic Input Voltages

Maximum Logic Low 0.8V

Minimum Logic High @ -1.6mA 2.3V (33ΩSeries terminations) Logic Output Voltage

(ALVCH16373 output buffer, V

= 2.5V) Maximum Logic Low @ 1.6mA 0.7V (33ΩSeries terminations)

Sampling Frequency (Convert Clock Frequency) See Table 1

Convert Clock Level 50 Ω Source Impedance, AC coupled or ground referenced

(Convert Clock input is capacitor coupled on board and ter-

minated with 50Ω.)

P-P 

2.5V

P-P

Sine Wave

or Square wave

Resolution See Table 1

Input frequency range See Table 1

SFDR See Applicable Data Sheet

SNR See Applicable Data Sheet

QUICK START PROCEDURE

Demonstration circuit 782 is easy to set up to evalu-

ate the performance of any of the LTC223X, LTC222X

or LTC224X family of A/D converters – LTC2236,

LTC2237, LTC2238, LTC2239, LTC2225, LTC2226,

LTC2227, LTC2228, LTC2229, LTC2245, LTC2246,

LTC2247, LTC2248, LTC2249, LTC2250, LTC2251

LTC2253, LTC2254, or LTC2255. Refer to Figure 1

for proper measurement equipment setup and follow

the procedure below:

SETUP

If a DC718 QuickDATS Data Acquisition and Test

System was supplied with the DC782 demonstration

circuit, follow the DC718 Quick Start Guide to install

the required software and for connecting the DC718 to

the DC782 and to a PC running Windows98, 2000 or

XP.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 782

10/12/14 BIT 10 TO 125 MSPS ADC

Figure 1.

DC782 Setup

DC782 DEMONSTRATION CIRCUIT BOARD JUMPERS

The DC782 demonstration circuit board should have

the following jumper settings:

JP1: SHDN: Ground, enables ADC core.

JP2: OE: Ground, enables digital outputs.

JP3: SENSE: Select VDD for the 2V

input range

SENSE: Select VCM for the 1V

input range.

JP4: MODE: Select VDD (For 2’s complement out-

put format for PScope compatibility) and disables

Clock Duty Cycle Stabilizer.

APPLYING POWER AND SIGNALS TO THE DC782

DEMONSTRATION CIRCUIT BOARD:

If a DC718 is used to acquire data from the DC782,

the DC718 must FIRST be connected to a powered

USB port or provided an external 6-9V BEFORE ap-

plying +3V across the pins marked “+3.0V” and

“PWR GND” on the DC782. The DC782 demonstra-

tion circuit requires up to 150 mA depending on the

sampling rate and the A/D converter supplied.

The DC718 data collection board is powered by the

USB cable and does not require an external power

supply unless it must be connected to the PC

through an un-powered hub in which case it must

be supplied an external 6-9V on turrets G7(+) and

G1(-) or the adjacent 2.1mm power jack.

Encode Clock

Analog Input

Parallel data output

TO QuickEval II or other

Data Acquisition System

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 782

10/12/14 BIT 10 TO 125 MSPS ADC

ENCODE CLOCK

NOTE: THIS IS NOT A LOGIC LEVEL INPUT. Apply

an encode clock to the SMA connector on the

DC782 demonstration circuit board marked

“CLOCK INPUT”. Refer to Table 2 for recommended

level, impedance and coupling. This input is con-

nected to ground through a 50Ω resistor. For the

very best noise performance, the CLOCK INPUT

must be driven with a very low jitter source. When

using a sinusoidal generator, the amplitude should

be as large as possible, up to 3V

P-P

. Using band

pass filters on the clock and the analog input will

improve the noise performance by reducing the

wideband noise power of the signals. Data sheet

FFT plots are taken with 10 pole LC filters made by

TTE (Los Angeles, CA) to suppress signal generator

harmonics, non-harmonically related spurs and

broad band noise. Low phase noise Agilent 8664B

generators are used with TTE band pass filters for

both the Clock input and the Analog input.

[The Encode Clock can be driven with a 2.5V CMOS

Logic Level square wave if C12 is replaced with a

jumper. Note that the cable carrying the clock sig-

nal must be terminated to maintain the signal integ-

rity of the Encode Clock Source. Therefore the sig-

nal source must be able to drive the 0 to 2.5V

square wave signal into 50Ω load.]

Apply the analog input signal of interest to the SMA

connector on the DC782 demonstration circuit

board marked “ANALOG INPUT”. This input is ca-

pacitive coupled to the primary of transformer T1.

The conversion clock output is available on pin 3 of

J2 and the data samples are available on

Pins 11-37 for 14 BITS or (15-37 for 12 BITS) or

(17-37 for 10 BITS) of J2. Data can be collected

via a logic analyzer, cabled to a development sys-

tem through a SHORT 2 to 4 inch long 40 pin rib-

bon cable or collected by the DC718 QuickEval-II

Data Acquisition Board using the

PScope System

Software

provided or down loaded from the Linear

Technology website at

http://www.linear.com/software/. If a DC718 was

provided, follow the DC718 Quick Start Guide and

the instructions below.

To start the data collection software if

“

PScope.exe

”, is installed (by default) in

\Program Files\LTC\PScope\, double click the

PScope Icon or bring up the run window under the

start menu and browse to the PScope directory and

select PScope.

Configure PScope for the appropriate variant of the

DC782 demonstration circuit by selecting the cor-

rect A/D Converter as installed on the DC782. Un-

der the “Configure” menu, go to “Device.” Under

the “Device” pull down menu, select device, either

LTC2236, LTC2237, LTC2238, LTC2239, LTC2225,

LTC2226, LTC2227, LTC2228, LTC2229, LTC2245,

LTC2246, LTC2247, LTC2248, LTC2249, LTC2250,

LTC2251 LTC2253, LTC2254, or LTC2255. If only a

14 BIT demonstration circuit was provided, 12 and

10 BIT performance can be simulated by selecting

the appropriate LTC222X or LTC223X part in the

Device List and PScope will automatically blank the

last two or four LSBs when using a DC782 supplied

with a 14 BIT part.

If everything is hooked up properly, powered and a

suitable convert clock is present, clicking the “Col-

lect” button should result in time and frequency

plots displayed in the PScope window. Additional

information and help for

PScope

is available in the

DC718 Quick Start Guide and in the online help

available within the

PScope

program itself.

ANALOG INPUT NETWORK

For optimal distortion and noise performance the

RC network on the analog inputs are optimized for

different analog input frequencies on the different

versions of the DC782. For input frequencies below

about 70 MHz, the circuit in Fig. 2 is recommended

(this is installed on DC782 versions

A,B,C,D,E,F,G,H, J,K,L,M,N,P). For input frequen-

cies above 70 MHz and below 170 MHz, the circuit

in Fig. 3 is recommended (this is installed on ver-

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 782

10/12/14 BIT 10 TO 125 MSPS ADC

sions Q, R, S, T, U, V, W, X). (This circuit will work

below 70MHz, down to below10MHz, but with de-

graded common mode rejection due to the fre-

quency response of the balun.)

For input frequencies between 170 MHz and

300 MHz, the circuit in Fig. 4 is recommended. For

input frequencies greater than 300 MHz contact the

factory for support.

Figure 2.

Analog Front End Circuit For 1MHz < A

< 70MHz

Figure 3.

Analog Front End Circuit For 70MHz < A

< 170MHz

1:1 BALUN

T1 = MA/COM ETC1-1T

RESISTORS AND CAPACITORS ARE 0402 PACKAGE SIZE

T1 = MA/COM ETC1-1-13

RESISTORS AND CAPACITORS ARE 0402 PACKAGE SIZE

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 782

10/12/14 BIT 10 TO 125 MSPS ADC

Figure 4.

Analog Front End Circuit For 170MHz < A

< 300MHz

1:1 BALUN

T1 = MA/COM ETC1-1-13

RESISTORS AND CAPACITORS ARE 0402 PACKAGE SIZE

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 782

10/12/14 BIT 10 TO 125 MSPS ADC