Several priciples was implemented in the double DDS design:
1. Every DDS board will be installed in separate case
2. Every DDS board contains three independent parts - AD9912 circuit, Power Supply circuit, Alias Filter circuit.
3. 1 GHz reference clock would have two output ports and will be installed to the special HM screening box.
4. All parts of the double DDS will be supplying from an extra 5V Power supply, installed inside the main box.
is based on the Analog Devices recomendations. Resistive dividers at the input of control lines they are necessary to adapt the level of control signals from 5V to 3.3V.
DDS Power Supply
contains three independent circuits with Linear Technology ICs for 3.3 VDC and 1.8 VDC, needed for AD9912 supplying. R18 and R19 values were changed from 10 Ohms to 18 Ohms each for better distribution of heat load on the PCB. U3 is the most heat IC on the PCB. The heat dissipation of this part and from the AD9912 chip is provided by two Alluminium pillars affixed to the Hammond case, with termal foil on the top side, touched PCB from the bottom.
DDS Alias Filter
is the same as Giuliano has developed for 240 MHz @ 3dB.