LINEAR TECHNOLOGY LTC2000-16 Demonstration Circuit Installation Guide
- June 16, 2024
- LINEAR TECHNOLOGY
Table of Contents
LINEAR TECHNOLOGY LTC2000-16 Demonstration Circuit Installation Guide
LTC2000, LTC2000A
16-, 14-, 11-Bit, 2.5Gsps to 2.7Gsps DACs
DESCRIPTION
Demonstration circuit 2085 supports the LTC®2000 and LTC2000A, a high speed, high dynamic range family of DACs. It was specially designed for applications that require differential DC coupled outputs. DC2085 supports the complete family of the LTC2000 including 16, 14 and 11 bit parts. For all the variations see Table 1.
The circuitry on the analog outputs is optimized for analog frequencies from DC-1.08GHz.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2085
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
of Analog
Devices, Inc. All other trademarks are the property of their respective
owners.
Table 1. DC2085 Variants
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
QUICK START PROCEDURE
DC2085 is easy to set up to evaluate the performance of the LTC2000. Refer to Figure 1 for proper measurement equipment set-up and follow the procedure below:
Setup
If the Altera Stratix IV GX FPGA Development Kit was not supplied with the
DC2085 demonstration circuit, follow the Altera Stratix IV demo manual to
install the required software and for connecting the Altera Stratix IV to the
DC2085 and to a PC.
Figure 1. DC2085 Setup (zoom for details)
HARDWARE SETUP
SMAs
J2 & J3: Differential Trigger Input. Apply a signal to J2 from a 50Ω driver.
Absorptive filters are required for data sheet performance. Use J2 and J3 if
the trigger is a differential signal.
J4: Sample Clock Input. Apply a clock signal to this SMA connector from a 50Ω driver. A 0dBm clock source should be sufficient, but for best phase noise and jitter performance, use the highest possible amplitude and slew rate, up to 15dBm.
J5 & J6: Differential Output Signals. These SMAs provide access to the differential outputs of the DAC. The output impedance is designed to be 50Ω at each SMA, or 100Ω differential. Connect an external balun or combiner to these pins to drive a single-ended spectrum analyzer. Linear Technology has various coupon boards for specific frequencies and applications. More information is available at www.linear.com.
J8: SYNC. This SMA is to provide access to the sync pin of the LT8614. It is not used in normal use.
Turrets
+5V: Positive Input Voltage for the DAC and Digital Circuits.
This voltage feeds a series of regulators that supply the proper voltages for
the DAC. The voltage range for this turret is 4.8V to 5.2V. Note: For close-in
phase noise plots, driving this voltage is not ideal. There is a known 20kHz
noise hump in the spectrum that is generated by the regulators. For the best
phase noise performance, back drive the onboard regulators with the provided
turrets from a low noise supply.
GND: Ground Connection. This demo board has only a single ground plane. This turret should be tied to the GND terminal of the power supply being used.
SVDD3V0: Optional 3.0V Input. This pin is connected directly to the SVDD pin of the DAC. It requires a supply that can deliver up to 100mA. Driving this pin will shut down the onboard regulator.
AVDD3V3: Optional 3.3V Input. This pin is connected directly to the AVDD3V3 pin of the DAC. It requires a supply that can deliver up to 200mA. Driving this pin will shut down the onboard regulator.
DVDD3V3: Optional 3.3V Input. This pin is connected directly to the DVDD3V3 pin of the DAC. It requires a supply that can deliver up to 50mA. Driving this pin will shut down the onboard regulator.
AVDD1V8: Optional 1.8V Input. This pin is connected directly to the AVDD1V8 pin of the DAC. It requires a supply that can deliver up to 1A. Driving this pin will shut down the onboard regulator.
DVDD3V3: Optional 1.8V Input. This pin is connected directly to the DVDD1V8 pin of the DAC. It requires a supply that can deliver up to 500mA. Driving this pin will shut down the onboard regulator.
VP1: This is a test point that is at the output of the onboard switching
regulator. It is meant for test purposes.
It can also be driven to 2.5V to shut down the output of the switching
regulator.
TSTP & TSTN: These pins are tied directly to the TSTP and TSTN pins of the DAC. They can be used to measure the internal temperature and timing of the LVDS inputs. FSADJ: This is an optional pin that is tied directly to the FSADJ pin of the DAC. It can be used to set the full-scale output current of the DAC. In normal operation this pin is tied to GND through 500Ω to set a current of 40mA at the output.
REFIO: This pin is tied directly to the REFIO pin of the DAC and is used to
set the reference voltage for the DAC.
Normally it is internally set to 1.25V but can be overdriven with an external
voltage from 1.1V to 1.4V.
Jumpers
The DC2085 demonstration circuit should have the following jumper settings as
default positions.
JP1: PD. In the RUN position this pin results in normal operation of the DAC.
In the SHDN position the DAC is powered down. (Default: RUN or up)
JP2: SPI and JTAG. This jumper selects how the FPGA is programmed. In the SPI position the FPGA is programmed from the onboard FTDI chip and the LTDACGen software. In the JTAG position the J9 is used with a JTAG programmer to program the FPGA. (Default: SPI or down)
Connectors
J1: DC590. This is an optional header that can be used to program the DAC with
the DC590. (Default: removed)
J9: JTAG. This is an optional header that can be used to program the FPGA
through a JTAG programmer. (Default: removed)
J7: USB. Connect a USB cable from J7 to a computer with the LTDACGen software
installed.
J10 & J11: HSMC Connectors. These connectors are designed to connect to the
Altera Stratix IV development board. All of the communication between the FPGA
and the DAC is routed through these connectors.
APPLYING POWER AND SIGNALS TO THE DC2085 DEMONSTRATION CIRCUIT
If a Stratix IV demo board is used to supply data to the DC2085, the two
boards should first be bolted together and a proper connection should be made.
If Linear Technology provided the Stratix IV board the proper bit file is
already installed in flash memory and will begin to operate when the board is
powered on. If an unprogrammed FPGA board is used, refer to the appropriate
documentation on how to program it.
Power should be applied to the system in this order:
- Connect the Altera board to the provided power supply.
- Connect the USB cable to J7.
- Apply a clock to J4.
- Connect any optional output board to J5 and J6.
- Turn on the voltage to the Altera board.
- Connect the 5V from a bench supply to the +5V turret on the DC2085.
- Open the LTDACGen software and hit connect.
LTDACGen should report back that it is connected to the FPGA. See Figure 2:
Figure 2. LTDACGen Connected to FPGA
ANALOG OUTPUT NETWORK
The analog output network of the DC2085 has been designed to maximize the
performance of the LTC2000.
The LTC2000 drives two 50Ω resistors on each side to minimize the impedance it
sees. This maximizes the SFDR the DAC is able to produce. If a larger signal
swing is required this impedance can be increased, but the SFDR might degrade.
The output also has a pi network of 50Ω resistors to pad the output impedance
of the board up to 50Ω per side. This allows the demo board to drive a 50Ω
analyzer through a balun or other combiner.
Linear Technology has various coupon boards for specific frequencies and applications. More information is available at www.linear.com.
SAMPLE CLOCK
The sample clock to the DC2085 demonstration circuit board is marked J4. As a
default it is a single-ended 50Ω input port. There is an onboard balun that
does a singleended to differential translation.
For the best noise performance, the sample input must be driven with a very
low jitter signal generator source.
The amplitude should be as large as possible up to ±1.8V or 9dBm.
SOFTWARE
The software for the DC2085, LTDACGen is available at www.linear.com free of
charge. It simplifies the creation of complex waveforms and loading them into
the FPGA to test the DC2085. For more information about how to use the
LTDACGen software, refer to the help files that come with the software.
RESULTS
After everything is set up and the software is connected to the DAC demo
system, a sine wave can be added to the output waveform. The default frequency
is 399.932861328MHz (Figure 3). By clicking Update FPGA, the data is sent to
the FPGA and is then used to program the DAC. A spectrum analyzer can then be
used to view the results (Figure 4).
Figure 3. Default Frequency
Figure 4. DC2085 Results. Close-In (Top) and Wideband (Bottom)
PARTS LIST
SCHEMATIC DIAGRAM
DEMONSTRATION BOARD IMPORTANT NOTICE
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following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear
Technology is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION
PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO
BOARD herein may not be complete in terms of required design-, marketing-,
and/or manufacturing-related protective considerations, including but not
limited to product safety measures typically found in finished commercial
goods. As a prototype, this product does not fall within the scope of the
European Union directive on electromagnetic compatibility and therefore may or
may not meet the technical requirements of the directive, or other
regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
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References
- Mixed-signal and digital signal processing ICs | Analog Devices
- Product Evaluation Boards and Kits | Design Center | Analog Devices
- LTC2000 Datasheet and Product Info | Analog Devices
- LTC2000A Datasheet and Product Info | Analog Devices