I am working with your DDS AD9835 but plan to migrate into your more advanced DDS chip AD9102. Would you please check my schematics and answer by questions below?
Please look at my schematics as in the attachment.
Description of the circuit:
RV1 is a potentiometer to adjust the amplitude of OSC_out signal. R3 and R4 are the fixed values to do the same thing. For the time being R3 is 0R and R4 is not populated. R2 is to bypass RV1 and not populated.
R4 will also be used for impedance matching.
OSC_TB522 (U1) is a 100 MHz square wave output TCXO with 1 ppm accuracy.
AC coupling is ensured by capacitor C18.
Since 3.3V supply is used DLDO1, DLDO2 and CLDO are all LDO outputs and bypassed by single capacitors.
Since internal REF is used REFIO pin is also bypassed with a capacitor.
R7 will be used in automatic calibration process and for the time being not populated.
CAL_SENSE pin is normally in no connect position.
R6 is 8.06K as in the AD9106 EVB.
PF0 - PF4 are the GPIO pins of the Blackfin DSP to control the DDS.
Q1-) What is the recommended value for R6?
Q2-) I prefer standard 4-wire SPI connection, Are MOSI -> SDIO and MISO -> SDO/SDI2/DOUT pin connections correct?
Q3-) What would be recommended values for R8, R9, R11 and R12?
Q4-) Should R10 be 0R and be populated?
Q5-) Any general comments about the schematics?