Darrell finally returned on the 19th.
There will be a few changes in the current schematics. I had overlooked some important facts.
DDS : no I-Q summing. Only the I ouputs will be used. Transformer solution for summing complementary currents is no good; as the LF response is not good enough. I will be looking for an opamp solution now. No other major changes here.
ADC: The inputs to the AD8022 needs a step-up by 2.5V. I used a non-inverting summing configuration. Darrell suggested a voltage divider configuration. Have to look into that.
SPARTAN3-Z8: the bus is finally there.
JTAG: confirmed daisy chain configuration. Need to fix schematics from master-slave.
Power supply: major changes. Found TPS75003 from TI - IC power supply for S3. Moreover, seems TI is dishing out samples. I will change my other two power ic's to TI.
USB: No change.
Attenuator: Darrell vaguely suggested some other config than using an IC - due to the LF response of RF2420. I am still convinced rf2420 will work - given right choice of input blocking capacitors. More work on that.
Footprints for the buttons need to be confirmed and designed.
The LPF response should be simulated and confirmed with Darrell.
PCB needs an update.
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