Linear Technology LTC2268-14 User manual

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1532
12/14 BIT, 25 TO 125 MSPS DUAL ADC
1
LTC2268-14, LTC2268-12, LTC2267-14, LTC2267-12, LTC2266-14, LTC2266-12, LTC2265-14,
LTC2265-12, LTC2264-14, LTC2264-12, LTC2263-14, LTC2263-12
DESCRIPTION
Demonstration circuit 1532 supports a family of 14/12
BIT 125 MSPS ADCs. Each assembly features one of
the following devices: LTC2268-14, LTC2268-12,
LTC2267-14, LTC2267-12, LTC2266-14, LTC2266-12,
LTC2265-14, LTC2265-12, LTC2264-14, LTC2264-12,
LTC2263-14, LTC2263-12 high speed, dual ADCs.
The versions of the 1532A demo board are listed in
Table 1. Depending on the required resolution and
sample rate, the DC1532 is supplied with the appropri-
ate ADC. The circuitry on the analog inputs is opti-
mized for analog input frequencies from 5 MHz to
140MHz. Refer to the datasheet for proper input net-
works for different input frequencies.
Design files for this circuit board are available. Call
the LTC factory.
LTC is a trademark of Linear Technology Corporation
Table 1. DC1532 Variants
DC1532
VARIANTS
ADC PART
NUMBER
RESOLUTION* MAXIMUM SAMPLE
RATE
INPUT FREQUENCY
1532A-A
LTC2268-14 14-BIT 125 Msps 5MHz-140MHz
1532A-B
LTC2267-14 14-BIT 105 Msps 5MHz-140MHz
1532A-C
LTC2266-14 14-BIT 80 Msps 5MHz-140MHz
1532A-D
LTC2265-14 14-BIT 65 Msps 5MHz-140MHz
1532A-E
LTC2264-14 14-BIT 40 Msps 5MHz-140MHz
1532A-F
LTC2263-14 14-BIT 25 Msps 5MHz-140MHz
1532A-G
LTC2268-12 12-BIT 125 Msps 5MHz-140MHz
1532A-H
LTC2267-12 12-BIT 105 Msps 5MHz-140MHz
1532A-I
LTC2266-12 12-BIT 80 Msps 5MHz-140MHz
1532A-J
LTC2265-12 12-BIT 65 Msps 5MHz-140MHz
1532A-K
LTC2264-12 12-BIT 40 Msps 5MHz-140MHz
1532A-L
LTC2263-12 12-BIT 25 Msps 5MHz-140MHz

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1532
12/14 BIT, 25 TO 125 MSPS DUAL ADC
2
Table 2. Performance Summary (TA= 25°C)
PARAMETER CONDITION VALUE
Supply Voltage – DC1532A Depending on sampling rate and the A/D converter
provided, this supply must provide up to 500mA.
Optimized for 3V
[3V 6.0V min/max]
Analog input range Depending on SENSE Pin Voltage 1 V
PP
to 2V
PP
Minimum Logic High 1.3V
Logic Input Voltages
Maximum Logic Low 0.6V
Nominal Logic levels (100Ωload, 3.5mA Mode) 350mV/1.25V com
mon mode
Logic Output Voltages (differential)
Minimum Logic levels (100Ω load, 3.5mA Mode) 247mV/1.25V common mode
Sampling Frequency (Convert Clock Fre-
quency)
See Table 1
Encode Clock Level Single ended Encode Mode (ENC- tied to GND) 0-3.6V
Encode Clock Level Differential Encode Mode (ENC- not tied to GND) 0.2V-3.6V
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 1532 is easy to set up to
evaluate the performance of the LTC2268 A/D
converters. Refer to Figure 1 for proper meas-
urement equipment setup and follow the proce-
dure below:
SETUP
If a DC1371 “PStache” Data Acquisition and Col-
lection System was supplied with the DC1532
demonstration circuit, follow the DC1371 Quick
Start Guide to install the required software and
for connecting the DC1371 to the DC1532 and to
a PC running Windows 2000 or XP.

3
Figure 1. DC1532 Setup (zoom for detail)
3.5-6V
+
Analog Inputs
Single Ended Encode Clock
(Use provided DC1075, di-
vide by 4 clock board)
Channel 1
Channel 2
To provided power supply
To provided USB cable
Parallel/Serial

4
DC1532 DEMONSTRATION CIRCUIT
BOARD JUMPERS
The DC1532 demonstration circuit board
should have the following jumper settings as
default positions: (as per Figure 1)
J13: PAR/SER : Selects Parallel or Serial pro-
gramming mode. (Default - Serial)
Optional Jumpers:
J8: Term: Enables/ Disable optional output
termination. (Default - Removed)
J5: ILVDS: Selects either 1.75mA or 3.5mA
of output current for the LVDS drivers. (De-
fault – Removed)
J14: LANE: Selects either 1 lane or 2 lane
output modes (Default – Removed) NOTE:
The DC1371 does not support 1 lane opera-
tion.
J15: SHDN: Enables and disables the
LTC2268. (Default - Removed)
J2: WP: Enable/Disables write protect for the
EEPROM. (Default – Removed)
Note: optional jumper should be left open to
ensure proper serial configuration.
APPLYING POWER AND SIGNALS TO THE
DC1532 DEMONSTRATION CIRCUIT
The DC1371 is used to acquire data from the
DC1532, the DC1371 must FIRST be con-
nected to a powered USB port and have 5V
applied power BEFORE applying +3.6V to
+6.0V across the pins marked “V+” and
“GND” on the DC1532. DC1532 requires 3.6V
for proper operation.
Regulators on the board produce the volt-
ages required for the ADC. The DC1532
demonstration circuit requires up to 500mA
depending on the sampling rate and the A/D
converter supplied.
The DC1532 should not be removed, or con-
nected to the DC1371 while power is applied.
ANALOG INPUT NETWORK
For optimal distortion and noise performance
the RC network on the analog inputs may
need to be optimized for different analog input
frequencies. For input frequencies above 140
MHz, refer to the LTC2268 datasheet for a
proper input network. Other input networks
may be more appropriate for input frequen-
cies less that 5MHz.
In almost all cases, filters will be required on
both analog input and encode clock to provide
data sheet SNR.
The filters should be located close to the in-
puts to avoid reflections from impedance dis-
continuities at the driven end of a long trans-
mission line. Most filters do not present 50Ω
outside the passband. In some cases, 3dB to
10dB pads may be required to obtain low dis-
tortion.
If your generator cannot deliver full scale sig-
nals without distortion, you may benefit from a
medium power amplifier based on a Gallium
Arsenide Gain block prior to the final filter.
This is particularly true at higher frequencies
where IC based operational amplifiers may be
unable to deliver the combination of low noise
figure and High IP3 point required. A high or-
der filter can be used prior to this final ampli-

5
fier, and a relatively lower Q filter used be-
tween the amplifier and the demo circuit.
Apply the analog input signal of interest to the
SMA connectors on the DC1532 demonstra-
tion circuit board marked “J3 AIN1”, “J4 AIN2”,
“J6 AIN3”, “J7 AIN4”. These inputs corre-
spond with channels 1-4 of the ADC respec-
tively. These inputs are capacitive coupled to
Balun transformers ETC1-1-13.
ENCODE CLOCK
NOTE: Apply an encode clock to the SMA
connector on the DC1532 demonstration cir-
cuit board marked “J11 CLK+”. As a default
the DC1532 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 3V
P-P
or 13dBm. When using a
sinusoidal signal generator a squaring circuit
can be used. Linear Technology also pro-
vides demo board DC1075A that divides a
high frequency sine wave by four, producing a
low jitter square wave for best results with the
LTC2268.
Using band pass filters on the clock and the
analog input will improve the noise perform-
ance by reducing the wideband noise power
of the signals. In the case of the DC1532 a
band pass filter used for the clock should be
used prior to the DC1075A. Datasheet FFT
plots are taken with 10 pole LC filters made by
TTE (Los Angeles, CA) to suppress signal
generator harmonics, non-harmonically re-
lated spurs and broadband noise. Low phase
noise Agilent 8644B generators are used for
both the Clock input and the Analog input.
DIGITAL OUTPUTS
Data outputs. data clock, and frame clock sig-
nals are available on J1 of the DC1532. This
connector follows the VITA-57/FMC standard,
but all signals should be verified when using an
FMC carrier card other than the DC1371.
SOFTWARE
The DC1371A is controlled by the PScope
System Software provided or downloaded
from the Linear Technology website at
http://www.linear.com/software/.
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 un-
der the start menu and browse to the PScope
directory and select PScope.
If the DC1532 demonstration circuit is prop-
erly connected to the DC1371, PSCOPE
should automatically detect the DC1532, and
configure itself accordingly.
If everything is hooked up properly, powered
and a suitable convert clock is present, click-
ing 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 DC1371A Quick
Start Guide and in the online help available
within the PScope program itself.

6
SERIAL PROGRAMMING
PScope has the ability to program the DC1532
board serially through the DC1371. There are
several options available in the LTC2268 family
that are only available through serially pro-
gramming. 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).
Figure 3: PScope Toolbar
This will bring up the menu shown in figure 4.
Figure 4: Demobd Configuration Options.
This menu allows any of the options available for
the LTC2268 family to be programmed serially.
The LTC2268 family has the following options:
Randomizer – Enables Data Output Random-
izer
- Off (Default) – Disables data output randomizer
- On – Enables data output randomizer
Two’s complement – Enables two’s comple-
ment mode
- Off (Default) – Selects offset binary mode
- On – Selects two’s complement mode
Sleep Mode – Selects between normal opera-
tion, sleep mode:
- Off (Default) – Entire ADC is powered, and ac-
tive
- On – The entire ADC is powered down.
Channel 1 Nap- Selects between normal opera-
tion and putting channel 1 in nap mode.
-Off (Default) – Channel one is active
- On – Channel one is in nap mode
Channel 2 Nap- Selects between normal opera-
tion and putting channel 2 in nap mode.
-Off (Default) – Channel two is active
- On – Channel two is in nap mode
Output Current – Selects the LVDS output drive
current
- 1.75mA (Default) - LVDS output driver current
- 2.1mA - LVDS output driver current
- 2.5mA - LVDS output driver current
- 3.0mA - LVDS output driver current
- 3.5mA - LVDS output driver current
- 4.0mA - LVDS output driver current
- 4.5mA - LVDS output driver current
Internal Termination – Enables LVDS internal
termination
- Off (Default) – Disables internal termination

7
- On – Enables internal termination
Outputs – Enables Digital Outputs
- Enabled (Default) – Enables digital outputs
- Disabled – Disables digital outputs
Test Pattern – Selects Digital output test pat-
terns. The desired test pattern can be entered
into the text boxes provided.
-Off(default) – ADC input data is displayed
-On – Test pattern is displayed.
Once the desired settings are selected hit OK
and PScope will automatically update the regis-
ter of the device on the DC1532 demo board.

8

9