Linear Technology LTC2270 Guida rapida alla configurazione

dc1975fa

DEMO MANUAL DC1975A

DESCRIPTION

LTC2270

16-Bit, 20Msps Dual ADC

Demonstration circuit 1975A supports the LT C

2270 high

speed, high dynamic range ADC. It was specially designed

for applicationsthat require differentialDC inputs. DC1975

supports the LTC2270 in CMOS output mode.

The circuitry on the analog inputs is optimized for ana-

log input frequencies from DC to 70MHz. Refer to the

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and PScope

and QuikEval are trademarks of Linear Technology Corporation. All other trademarks are the

property of their respective owners.

PERFORMANCE SUMMARY

DC1975 VARIANTS

data sheet for proper input networks for different input

frequencies.

Design files for this circuit board are available at

http://www.linear.com/demo

PARAMETER CONDITIONS MIN TYP MAX UNITS

Supply Voltage: DC1975A Depending on Sampling Rate and the A/D Converter

Provided, This Supply Must Provide Up to 300mA

4.5 6 V

Analog Input Range Depending on SENSE Pin Voltage 1 2.1 VP-P

Logic Input Voltages Minimum Logic High

Maximum Logic Low

1.3

0.6

Sampling Frequency (Convert Clock

Frequency)

1 20 Msps

Convert Clock Level Single-Ended Encode Mode (ENC– Tied to GND) 0 3.6 V

Convert Clock Level Differential Encode Mode (ENC– Not Tied to GND) 0.2 3.6 V

Resolution 16

Input Frequency Range DC 70 MHz

DC1975 VARIANTS ADC PART NUMBER RESOLUTION MAXIMUM SAMPLE RATE INPUT FREQUENCY

1975A LTC2270 16-Bit 20Msps DC to 70MHz

Specifications are at TA= 25°C

dc1975fa

DEMO MANUAL DC1975A

QUICK START PROCEDURE

DC1975A is easy to set up to evaluate the performance of

the LTC2270 A/D converter. Refer to Figure 1 for proper

measurement equipment setup and follow the procedure

in the Setup section.

SETUP

The DC890 USB demonstration circuit was supplied with

the DC1975 demonstration circuit. Follow the DC890

Quick Start Guide to install the required software and for

connecting the DC890 to the DC1975 and to a PC.

Figure 1. DC1975A Setup

dc1975 F01

SINGLE-ENDED ENCODE

CLOCK FROM DC1075

DIFFERENTIAL

ANALOG INPUT

CHANNEL 2

JUMPERS ARE SHOWN

IN DEFAULT POSITIONS

PARALLEL DATA

OUTPUT TO DC890

DIFFERENTIAL

ANALOG INPUT

CHANNEL 1

4.5V TO 6V

dc1975fa

DEMO MANUAL DC1975A

HARDWARE SETUP

SMAs:

J1 AIN1+ and J2 AIN1–: Differential Inputs for Channel 1.

Apply a differential signal to these SMA connectors from

a differential driver. There are 50Ω resistors at the end of

each transmission line that serve as termination for the

differential driver. These SMAs are positioned 0.8" apart

to accommodate LT C differential driver boards.

J3 AIN2+ and J4 AIN2–: Differential Inputs for Channel 2.

Apply a differential signal to these SMA connectors from

a differential driver. There are 50Ω resistors at the end of

each transmission lines that serve as termination for the

differential driver. These SMAs are positioned 0.8" apart

to accommodate LT C differential driver boards.

J5 ENC+: Positive Encode Clock Input. As a default the

demo board is populated to accept a single-ended clock

input from aDC1075Ademo board, or an equivalent CMOS

signal. For other population options see the Encode Clock

section of this manual.

J6 ENC–: Negative Encode Clock Input. As a default this

input port is grounded to accommodate the single ended

clock drive. For other population options see the Encode

clock section of this manual.

TURRETS:

V+ (TP5): Positive Input Voltage for the ADC and Digital

Buffers. This voltage feeds a regulator that supplies the

proper voltages for the ADC and buffers. The voltage range

for this turret is 4.5V up to 6V.

EXT REF (TP1): Optional Reference Programming Volt-

age. This pin is connected directly to the SENSE pin of

the ADC. If no external voltage is supplied this pin will be

pulled to VDD through a weak pull-up resistor. This will

select the ±1V input range. Connect to GND to select the

±0.5V input range, an external reference between 0.625V

and 1.3V will select an input range of ±0.8 • VSENSE.

GND (TP2, TP6, TP7): Ground Connection. This demo

board only has a single ground plane. One of these turrets

should be tied to the GND terminal of the power supply

being used. Extra GND pins are available for convenience

when probing.

VCM1 (TP3): Common-Mode Voltage for Channel 1. This

turret provides the common-mode voltage from the ADC

for channel 1. It is meant to be used to bias the common-

mode bias pin of the differential driver.

VCM2 (TP4): Common-Mode Voltage for Channel 2. This

turret provides the common-mode voltage from the ADC

for channel 2. It is meant to be used to bias the common-

mode bias pin of the differential driver.

JUMPERS:

The DC1975A demonstration circuit board should have

the following jumper settings as default positions (as per

Figure 1) which configures the ADC in serial programming

mode.Inthedefault configuration JP3-JP6shouldbeleftin

the default locations. This will pull those pins high through

weak pull-up resistors so that the SPI commands can be

sent from the PC. When JP2 is set to PAR, then jumpers

JP3-JP6 can be configured manually.

JP1 WP: EEPROM Write Protect. For factory use only.

Should be left in the enable (EN) position.

JP2 PAR/SER: Selects Parallel or Serial Programming

Mode. (Default: serial)

JP3 Duty Cycle Stab: In parallel programming mode

enables or disables duty cycle stabilizer. In serial program-

ming mode, pull up to VDD. (Default: Enable or pull up)

JP4 SHDN: In parallel programming mode enables or

disables LTC2270. In serial programming mode, pull up

to VDD. (Default: Enable or pull up)

JP5NAP:Inparallelprogrammingmode enables ordisables

NAP mode. In serial programming mode, pull up to VDD.

(Default: Enable or pull up)

JP6 LVDS/CMOS: In parallel programming mode selects

between LVDS or CMOS output signaling. In serial pro-

gramming mode, pull up to VDD. (Default: LVDS or pull

up). Note: In parallel mode CMOS mode must be selected.

LVDS mode not supported on the DC1975 demo board.

dc1975fa

DEMO MANUAL DC1975A

ANALOG INPUT NETWORK

APPLYING POWER & SIGNALS TO THE DC1975 DEMONSTRATION

CIRCUIT

In the default setup both of the inputs are brought out to

SMA connectors so the demo board can be driven with

a differential source. The DC1975 is populated with no

filtering between the input SMAs and the ADC. There are

provisions for a custom filter to be designed and installed

between the off board driver and ADC.

A common-mode voltage is provided on turrets TP3 and

TP4 that can be used to bias the driver. If the driver is sup-

plying the common-mode voltage R10 and R20 should be

removed, and the common-mode voltage from the driver

can be connected on turrets TP3 and TP4.

In almost all cases, off-board filters will be required on the

analog inputs of the differential driver boards to achieve

data sheet SNR.

The off-board filters should be located close to the inputs

of the differential driver board to avoid reflections from

impedance discontinuities at the driven end of a long

transmission line. Most filters do not present 50Ω outside

the passband. In some cases, 3dB to 10dB pads may be

required to obtain low distortion.

Apply the analog input signal of interest to the SMA

connectors on the DC1975 demonstration circuit board

marked J1-J4.

If a DC890 is used to acquire data from the DC1975, the

DC890 must FIRST be connected to a powered USB port

or provided an external 6V to 9V BEFORE applying 4.5V to

6V across the pins marked V+ and GND on the DC1975.

DC1975 requires 4.5V for proper operation. Regulators

on the board produce the voltages required for the ADC.

The DC1975 demonstration circuit requires up to 300mA

depending on the sampling rate and the A/D converter

supplied.

The DC890 data collection board is powered by the USB

cable and does require an external power supply when

collecting data from an LVDS demo board. It must be

supplied an external 6V to 9V on turrets G7(+) and G1(–)

or the adjacent 2.1mm power jack.

dc1975fa

DEMO MANUAL DC1975A

ENCODE CLOCKENCODE CLOCK

CLOCK NETWORK

Apply an encode clock to the SMA connector on the

DC1975A demonstration circuit board marked J5. As a

default, the DC1975A is populated to have a single-ended

input.

For the best noise performance, the ENCODE INPUT must

be driven with a very low jitter, square wave source. The

amplitude should be large, up to 3VP-P or 13dBm. When

using a sinusoidal signal generator, a squaring circuit

can be used. Linear Technology also provides DC1075A,

a demo board that divides a high frequency sine wave by

four, producing a low jitter square wave for best results

with the LTC2270.

Using a bandpass filter on the clock will improve the noise

performance by reducing the wideband noise power of the

signal. In the case of the DC1975, a bandpass filter used

for the clock should be used prior to the DC1075A. Data

sheet FFT plots are taken with 10 pole LC filters made

by TTE (Los Angeles, CA) to suppress signal generator

harmonics, nonharmonically related spurs and broadband

noise. Low phase noise Agilent 8644B generators are used

with TTE bandpass filters for both the clock input and the

analog inputs.

An internally generated conversion clock output is

available on P1, which could be collected via a logic

analyzer, or other data collection system if populated

with a SAMTEC MEC8-150 type connector or collected

by the DC890 QuikEval™ II data acquisition board using

PScope™ software.

The clock network on the DC1975 can support a variety of

clock inputs. As a default it is populated to accept a single

ended square wave clock from a DC1075 or appropriate

signal generator. This will drive the ENC+ pin single ended

and the ENC– pin on the ADC is tied to GND.

When using a single-ended sine wave generator to drive

the encode input of the ADC, it is best to use a single-

ended-to-differential translation circuit. To modify the

DC1975 to accommodate this first move the 0Ω resistor

populated in position R26 to position R28, and move R27

and R37 to the R29 and R34 locations. This will direct

the signal through the transformer T1 which will do the

single ended to differential translation.

When using a PECL or LVDS clock you can drive the

DC1975 differentially through J5 and J6. From the default

population, remove the 0ohm resistor in the C32 position

and add the appropriate termination for your clock signal.

R24, R25, R32, R38 and R39 are available to provide the

proper termination for LVDS, PECL, or CML signaling.

Blocking capacitors can be installed in the R30 and R35

positions if the common-mode voltage of the clock is not

compatible with the LTC2270.

dc1975fa

DEMO MANUAL DC1975A

Figure 2. ADC Configuration Figure 3. PScope Toolbar

SOFTWARE

The DC890 is controlled by the PScope system software

provided or downloaded from the Linear Technology

website at http://www.linear.com/software/. If a DC890

was provided, follow the DC890 Quick Start Guide and

the instructions below.

To start the data collection software if PScope.exe is in-

stalled (by default) in \Program Files\LT C \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.

If the DC1975 demonstration circuit is properly connected

to the DC890, PScope should automatically detect the

DC1975A, and configure itself accordingly. If necessary,

the following procedure explains how to manually con-

figure PScope.

UndertheConfiguremenu, go to ADC Configuration. Check

the Config Manually box and use the following configura-

tion options (see Figure 2).

Manual Configuration Settings:

Bits: 16

Alignment: 16

FPGA Ld: CMOS

Channs: 2

Bipolar: Unchecked

Positive-Edge Clk: Unchecked

If everything is hooked up properly, powered and a suit-

able convert clock is present, clicking the Collect button

should result in time and frequency plots displayed in

the PScope window. Additional information and help for

PScope is available in the DC890 Quick Start Guide and in

the online help available within the PScope program itself.

SERIAL PROGRAMMING

PScope has the ability to program the DC1975 board

serially through the DC890. There are several options

available in the LTC2270 family that are only available

through serially programming. PScope allows all of these

features to be tested.

These options are available by first clicking on the Set

Demo Bd Options icon on the PScope toolbar (Figure 3).

This will bring up the menu shown in Figure 4.

dc1975fa

DEMO MANUAL DC1975A

SOFTWARE

Figure 4. Demobd Configuration Options

This menu allows any of the options available for the

LTC2270 family to be programmed serially. The LTC2270

family has the following options:

Power Control: Selects between normal operation, nap

and sleep modes

n Normal (default): Entire ADC is powered and active

n Ch1 Normal Ch2 Nap: Channel 1 remains active while

channel 2 is put into nap mode

n Nap: ADC core powers down while references stay

active

n Shutdown: The entire ADC is powered down

Clock Inversion: Selects the polarity of the CLKOUT signal

n Normal (default): Normal CLKOUT polarity

n Inverted: CLKOUT polarity is inverted

Clock Delay: Selects the phase delay of the CLKOUT signal

n None (default): No CLKOUT delay

n 45 Deg: CLKOUT delayed by 45 degrees

n 90 Deg: CLKOUT delayed by 90 degrees

n 135 Deg: CLKOUT delayed by 135 degrees

Clock Duty Cycle: Enable or disables duty cycle stabilizer

n Stabilizer off (default): Duty cycle stabilizer disabled

n Stabilizer on: Duty cycle stabilizer enabled

Output Current: Selects the LVDS output drive current.

(Not supported by DC1975A)

n 1.75mA (default): LVDS output driver current

n 2.1mA: LVDS output driver current

n 2.5mA: LVDS output driver current

n 3mA: LVDS output driver current

n 3.5mA: LVDS output driver current

n 4mA: LVDS output driver current

n 4.5mA: LVDS output driver current

Internal Termination: Enables LVDS internal termination.

(Not supported by DC1975A)

n Off (default): Disables internal termination

n On: Enables internal termination

Outputs: Enables Digital Outputs

n Enabled (default): Enables digital outputs

n Disabled: Disables digital outputs

Output Mode: Selects digital output mode

n Full Rate (default): Full rate CMOS output mode.

n Double LVDS: Double data rate LVDS output mode.

(This mode is not supported by the DC1975A)

n Double CMOS: Double data rate CMOS output mode.

(This mode is not supported by the DC1975A)

dc1975fa

DEMO MANUAL DC1975A

PARTS LIST

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 1 CN1 CAP, X5R, ARRAY, 2.2µF, 20%, 4V, 0508 AVX, W2L14D225MAT1A

2 2 C1, C5 CAP, 0402 2.2µF, 20%, 6.3V, X5R TAIYO YUDEN, JMK105BJ225MV-F

3 0 C2, C3, C6, C12, C13, C14, C22, CAP, 0402 OPT

4 5 C4, C8, C9, C11, C18 CAP, 0402, 1µF, 10%, 16V, X6S TDK, C1005X6S1C105K

5 6 C7, C10, C15, C16, C17, C19 CAP, 0402, 0.01µF, 10%, 16V, X7R AVX, 0402YC103KAT2A

6 5 C20, C21, C23, C30, C31 CAP, 0402, 0.1µF, 10%, 10V, X5R TDK, C1005X5R1A104K

7 12 C24-C29, C33-C38 CAP, 0603, 0.1µF, 10%, 50V, X7R TDK, C1608X7R1H104K

8 3 C39, C40, C41 CAP, 0603, 22pF, 5%, 16V, NPO AVX, 0603YA220JAT2A

9 1 C42 CAP, 0603, 4.7µF, 20%, 6.3V, X5R TDK, C1608X5R0J475MT

10 4 C43, C45, C46, C48 CAP, 0603, 1µF, 10%, 16V, X7R TDK, C1608X7R1C105K

11 2 C44, C47 CAP, 0805, 10µF, 10%, 16V, X5R MURATA, GRM21BR61C106KE15L

Test Pattern: Selects digital output test patterns

n Off (default): ADC data presented at output

n All Out =1: All digital outputs are 1

n All Out = 0: All digital outputs are 0

n Checkerboard: OF and D13-D0 alternate between

101 0101 1010 0101 and 010 1010 0101 1010 on

alternating samples

n Alternating: Digital outputs alternate between all 1’s

and all 0’s on alternating samples

Alternate Bit: Alternate bit polarity (ABP) mode

n Off (default): Disables alternate bit polarity

n On: Enables alternate bit polarity. Before enabling

ABP, be sure the part is in offset binary mode

Randomizer: Enables data output randomizer

n Off (default): Disables data output randomizer

n On: Enables data output randomizer

Two’s complement: Enables two’s complement mode

n Off (default): Selects offset binary mode

n On: Selects two’s complement mode

Once the desired settings are selected, hit OK and PScope

will automatically update the register of the device on the

DC1975A demo board.

SOFTWARE

dc1975fa

DEMO MANUAL DC1975A

PARTS LIST

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

12 6 JP1, JP2, JP3, JP4, JP5, JP6 HEADER, 3-PIN, 2mm SULLIN, NRPN031PAEN-RC

13 6 J1-J6 CONN, SMA 50Ω EDGE-LAUNCH E.F.JOHNSON, 142-0701-851

14 0 L1 IND, 0603, BEAD TBD

15 3 L2, L3, L4 FERRITE BEAD, 1206 MURATA, BLM31PG330SN1L

16 9 RN1-RN9 RES, THICK FILM ARRAY, 33Ω VISHAY, CRA04S08333R0JTD

17 1 R1 RES, 0402, 1kΩ, 5%, 1/16W VISHAY, CRCW04021K00JNED

18 15 R2, R3, R7, R8, R11, R12, R17, R18,

R26, R27, R30, R35, R36, R37, C32

RES, 0402, 0Ω, JUMPER NIC, NRC04ZOTRF

19 10 R4, R5, R9, R10, R13, R16, R19,

R20, R31, R33

RES, 0402, 49.9Ω, 1%, 1/16W NIC, NRC04F49R9TRF

20 3 R6, R24, R39 RES, 0402, 100Ω, 1%, 1/16W NIC, NRC04F1000TRF

21 4 R14, R21, R22, R23 RES, 0402, 4.99kΩ, 1%, 1/16W NIC, NRC04F4991TRF

22 1 R15 RES, 0402, 100kΩ, 5%, 1/16W NIC, NRC04J104TRF

23 0 R25, R28, R29, R32, R34, R38 RES, 0402 OPT

24 1 R40 RES, 0603, 10kΩ, 5%, 1/10W NIC, NRC06J103TRF

25 5 R41, R42, R43, R44, R45 RES, 0603, 1kΩ, 5%, 1/10W VISHAY, CRCW06031K00JNED

26 2 R46, R48 RES, 0603, 3kΩ, 1%, 1/10W VISHAY, CRCW06033K00FKEA

27 1 R47 RES, 0603, 180kΩ, 1%, 1/10W VISHAY, CRCW0603180KFKED

28 1 R49 RES, 0603, 330kΩ, 1%, 1/10W VISHAY, CRCW0603330KFKEA

29 7 TP1-TP7 TP, TURRETS, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0

30 1 T1 XFMR, 1:1, TRANS-MABA-007159 MACOM, MABA-007159-000000

31 1 U1 IC, LTC2270CUP, QFN64UP-9×9 LINEAR TECHNOLOGY, LTC2270CUP

32 4 U2, U3, U5, U6 IC, 8-BIT DUAL VOLTAGE SUPPLY

TRANSLATOR, MICROPAK-10

FAIRCHILD SEMI., FXLH42245MPX

33 1 U4 IC, 2-BIT DUAL VOLTAGE SUPPLY

TRANSLATOR, MICROPAK-10

FAIRCHILD SEMI., FXL2T245L10X

34 1 U7 IC, ULP INVERTER, SC70-5 FAIRCHILD SEMI., NC7SP14P5X

35 1 U8 IC, EEPROM, TSSOP8 MICROCHIP TECH., 24LC025-I/ST

36 1 U9 IC, 8-BIT I/0 EXPANDER, SSOP20G NXP, PCF8574TS/3

37 2 U10, U11 IC, SINGLE RESISTOR LOW DROPOUT

REGULATOR, DFN8DD

LINEAR TECHNOLOGY, LT3080EDD

38 6 SHUNTS FOR JP1-JP6 SHUNT, 2mm SAMTEC, 2SN-BK-G

39 4 STANDOFF, SNAP-ON KEYSTONE, 8831

40 2 STENCILS FOR BOTH SIDES DC1975A-1

dc1975fa

DEMO MANUAL DC1975A

SCHEMATIC DIAGRAM

Figure 5. 2-Channel, High Speed, Low Power ADC Family, LVDS

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