AD9954 EME165 DDS KIT
 Thursday 5th January 2011

• EME165 KIT DESCRIPTION:
• KIT CONSTRUCTORS ALERT:
• KIT CHANGES & MODIFICATIONS:
• ORDER A EME165 DDS KIT
  
  

EME165 KIT DESCRIPTION

Please Note: that all information including pictures on this web page are copyright to Mini-Kits & must not be used on any other web site.

The circuit description below is for those that are wanting to know if this Kit is suitable for their own application. The Kit comes complete with detailed circuit & construction information, including schematic & board overlay diagrams.

The EME165 PC Board was designed to use a AD9954 14 bit 400MHz chip but can be used with any of the AD995X series chips. The Kit is for advanced constructors only that have experience in soldering fine pitched components. This Kit may be a challenge for many due to the very fine pitched Integrated circuits that are used on the board. Many of the other conventional sized SMD components are easily fitted. Do not attempt to build this Kit unless you are confident that you can successfully complete it, as the cost of repairs could be as much as a new Kit. When buying a full Kit, Mini-Kits offers a service to fit the Integrated circuits at extra cost.

The board or Kit can be used with many of the DDS VFO projects, or Software for the AD9954 that can be found on the WEB. The AD9954 is a +3.3v device & has been interfaced to a 16 Pin IDC I/O header plug C1 using an ADG3300 +3.3v to +5v voltage translator chip. These chips are much better than using voltage divider resistors, & allow two way high speed bidirectional data to be sent between the DDS & Micro controller.

The 16 Pin IDC I/O connector ( C1 ), has the following pin connections available. The connections in Red are +5v translated, & the Blue are direct +3.3v connections to the DDS chip. As the ADG3300 chip only has 8 translators, only 8 data connections on the DDS can be translated from +3.3v to +5v. It was decided to just use the common connections that are normally used in AD9954 DDS projects. If you are going to require the non translated +3.3v connections for your project, then you may have to use another ADG3300 chip. Alternatively if you are using low data rates you may be able to get away with using simple 2 resistor voltage divider to drop the +5v from your Micro controller to +3.3v. When using two AD9954 boards to provide I/Q outputs, the sync out & sync in, & also clock out & clock in can be directly connected as they are all +3.3v. The HF-DDS software does not currently support the use of two EME165 DDS boards for I/Q.

16 Pin IDC I/O connector ( C1 )

A number of resistors, R1, R2, & R3 are used on the board as links that may not be required for your application, but are required when using the EME150 PIC Controller & HF-DDS software. See the Kit schematic & board overlay diagrams for where the resistors are located.

The DDS output uses a 175MHz 7th order elliptic Low Pass Filter, which is used to reduce the aliases & quantization noise from the DAC outputs. This allows us to use the maximum recommended output frequency of 160MHz from the DDS for a 400MHz clock. A 1:1 Transformer is used on the DAC outputs which has the benefit of reducing even order harmonics, & produces +3dBm more output power. A Gali amplifier with a gain of +25dB & a IP3 of +38dBm was chosen as it was much lower cost compared to more complex amplifier designs. The DAC current RSET has been adjusted to provide a very good Spurious Free Dynamic Range, & drives the high gain Gali device to around 1/2 its capable output power to produce a clean +10dBm output. With reference to the fundamental output @ 0dBm, the 100MHz clock is -45dB, 2nd Harmonic -36dBc, 3rd -54dBc, all other spurs > -50dBc

The PC Board uses plated through holes & separate analogue & digital ground planes, & power supplies to reduce noise. The AD9954 requires 3 power supply voltages so the board has two +1.8v regulators for analogue & digital supplies, & a +3.3v regulator for the digital I/O supply. All the chips & regulators run quite cool compared to the older AD985X series DDS chips.

The standard clock module that can be ordered for the Kit is a 100MHz 3.3v HY-Q QSMO-4213B 10ppm CMOS 5x7mm module. The board can also be fitted with a standard 9x14mm DIP package but it must be +3.3v, ( +5v types cannot be used & many damage the AD9954 clock input ). Many CMOS clock modules produce far too much output so a resistor is used on the board to reduce the output so that the AD9954 is not overdriven. The board also has a connector C3 that is suitable for feeding in your own clock or for extraction of the clock to feed into another AD9954 board.

Connector C2 allows interfacing to the AD9954 internal high speed comparator. The comparator can be used to produce a square wave clock from the RF output suitable for switching mixers. Please refer to the AD9954 data sheet.

EME165 KIT CONSTRUCTORS ALERT

If you are soldering the AD9954 & TXB0108P chips to the board. Please remove the excess solder from the tracks on the board using solder wick before soldering both chips to the board.

KIT CHANGES & MODIFICATIONS

1/ A problem occured when the HF-DDS software when first powered up could not recognise the AD9954 chip. The fault was traced to a faulty TXB0108PWR level converter chip on the EME165 DDS board.

2/ No RF output from the DDS board. Check with a sensitive receiver tuned to the DDS output frequency to see if it is actually outputting RF. If it appears to be working & that the RF output is just low go to 3 below. Check that the 100MHz oscillator module is working. Most problems can be due to bad solder joints on the AD9954 & TXB108PWR chips. Recheck that all pins on the these chips are soldered to the tracks on the board, & that there are no bridges between pins. A good magnifying glass & light is required to clearly see the connections. Sometimes pressing down on the AD9954 chip can make the DDS work. If you have developed your own software refer to 4 below.

3/ Low RF output from the DDS Board. There are a number of things that can cause this. The most common is, bad solder joints on the I & Q output pins of the AD9954 DDS, or one of the chip capacitors in the RF path being cracked. Other things that can cause this is, the 10uH choke not being soldered to the board, or one of the Gali-84 leads being shorted to ground, which turned out to be a solder bridge under the Gal-84 pins.

4/ Using the EME165 DDS board with your own software. Please make sure that you are using the links on the board correctly to suit your software. This has been a common problem experienced by a number of constuctors that have written their own software & could not make the board work. The reset line to the AD9954 chip will need to be pulled low in software from the microcontroller to reset to DDS. Mini-Kits is not able to supply software support on how to write your software to talk to the AD9954.

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