How to use the AD9874 EVAL-BOARD to receive a IF singal which frequency is approximate 15MHz? What the regesiter LOB, LOA, LOR numeber should be set?
And what is the relationship between Flo and IF? Does it means IF= FLO+2.25MHz?
I believe the default setting on the AD9874 EVB is for a 18 MHz clock frequency generated from the 26 MHz XO. Refer to Figure 13 in start-up guide that indicates that SPI initialization file configures the device for CLK=18 MHz and LO SYN=107.5 MHz. The Maxim silicon VCO on the EVB does not support an LO frequency of 18 MHz.I would suggest using an external generator to supply the 18 MHz LO into J1 connector (refer to Table I and Figure 5 in start-up guide). You can disable the LO Syn via Reg 0x00 in SPI Control GUI
If you want...........you could also use same signal (use power splitter) to drive the EXT CLK INPUT (J3 connector) while referring to Table II and figure 6a. In this case, you should also disable the CLK Synthesizer and Oscillator Bias in Reg 0x00 via SPI GUI.
A 15 MHz would be considered on the lower end of the IF's that are typically used for the AD9874.
The AD9874 actually consists of two IF's with the 1st being the mixer input and the 2nd being the ADC input (i.e. mixer output). Since the ADC's IF is fixed at CLK/8 that the relationship between the IF, FLO and CLK is as follows: >>> IF=FLO +/- CLK/8.
Since you LO is low enough, it is possible to make the FLO equal to the CLK rate to achieve a 15 MHz IF. Replacing FLO with CLK and assuming high-side injection (i.e. FLO>IF) one has the following relationship.>>> IF=7/8*CLK
If the IF is at 15 MHz than one can set CLK to 17.142857 MHz.If you could accept an IF of 15.75 MHz than you can use an CLK=18MHz.Note.............you can reconfigure the AD9874 EVB so that you can drive a CLK signal into both the LO and CLK inputs of the AD9874,
Thank you provide very useful infomation to me, but I am still confused that
If you could accept an IF of 15.75 MHz than you can use an CLK=18MHz. Does it means set the CKN and CKR so that can get the CLK=18MHz? Can I set the CNK=72, CKR=104?
For IF of 15.75MHz, what is the recommended LOA, LOB and LOR value?
Got it, thank you again.
Retrieving data ...