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how to use ad9142a Fs/4 modulation

I use NCO in fpga,generate 5M cos and sin to I and Q of AD9142A,

I use 100M for dac refclk, use 4x interpolate to set fdac=400M,

cmd_0x15=0xc9;//fREFCLK/fDIG = 16,fVCO/fDACCLK = 4,fDACCLK/fREFCLK = 4,

cmd_0x28=0x02;//4× mode; use HB1 and HB2 filters.

cmd_0x28 =0x04,(bit2 is FS4_MODULATION_ENABLE),

but can not get the 100M+5M,only get 5M signal

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but when i set 0x27=0x40(use NCO in AD9142A to generate 100M carrier),  can get 100+5M signal.

cmd_0x31=0x00;//FTW[7:0],100M carrier@400M

cmd_0x32=0x00;//FTW[15:8],100M carrier@400M

cmd_0x33=0x00;//FTW[23:16],100M carrier@400M

cmd_0x34=0x40;//FTW[31:24],100M carrier@400M

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so who can tell how to use Fs/4 modulation?

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