Evaluation board: AD9266-80EBZ.
Changes: I have changed the power so that DRVDD is 3.3V.
Problem: The signal level on the digital output is not going to GND. Here is a scope trace. CH1 (yellow) is the input signal. CH2 (blue) is D15/D14 (for this input signal the MSB is 1 on the peak and 0 in the trough) measured before RN808 and the buffer.
Is it normal for the output to sit at an indeterminate level like this? The datasheet doesn't mention anything about using a pull-down on the digital line, and I don't see one included in the evaluation board (apart from the PULLDOWN specified in the ucf file).
The output from Visual Analog (HSC-ADC-EVALCZ evaluation board) is attached below.
1)Thanks for trying the drive strength adjustment. I should have mentioned this earlier; the different fields in Register 0x15 are enabled/disabled by Bit in Register 0x14. For example, the default value of Register 0x14[7:0] = 0x00, which means that Register 0x14 Bit = 0. This enables the 3.3V fields in Register 0x15, which are Bits[7:6] and Bits[3:2]. So for the Register 0x15 values of 0xE2, 0xA2 or 0x62, you should have seen some change in DCO, but no change in data.
If by chance you used the non-default value of Register 0x14[7:0] = 0x80, then Register 0x14 Bit = 1. This enables the 1.8V fields in Register 0x15, which are Bits[5:4] and Bits[1:0]. In this case, for the Register 0x15 values of 0xE2, 0xA2 or 0x62, you should have seen some a minor change in DCO, but again no change in data.
Table 16 in the AD9266 datasheet shows these fields.
Is Register 0x14 at default? Were you looking at DCO or data? Please let me know if the above needs more explanation.
2)Your regulator modifications look to me like they should work, though in this scheme, U102 powers 3.3V_AMPVDD, DUT_DRVDD and AUX_DVDD, and U104 and U105 are unused.Please make sure you have a jumper on J503 between Pin 1 and Pin 2, to make sure that U501 is powered down. I don't expect that ADP1706 would have any trouble supplying current to these three domains, but you might want to check their voltages as a sanity check.
If you are seeing any supply drop, perhaps a more direct way to do a similar thing, but shares the load, would be to:- Remove E105 (which you already did)
- Leave E107 in place.- Solder across E108 (which you already did)- Leave everything else as it was before your modifications.
This way DUT_DRVDD and AUX_DVDD are supplied by U105, and 3.3V_AMPVDD is supplied by U102
3)In bypassing the baluns, did you remove them and jumper the traces, or wire around them? Regardless, the analog input network should not affect the output levels, unless somehow the grounds were affected.