Hi all,
I'm confused about how quadrature sampling is done with different daughterboards. I noticed the
daughterboard FAQ says the TVRX is "not a quadrature board."
It says:
"Because we're using the digital up converter in the AD9862 in 'Dual
Channel Complex DAC Data Mode', both D/A outputs are related (I&Q)
and as a result, all TX daughterboards are 'quadrature' boards. On the
receive side we've got a bit more variation. The TV_RX board (for
example) is
not a quadrature board, since it only uses a single A/D."
I've looked at the mux value (0xF0F0F0F0) set by determine_rx_mux_value() for the TVRX, and sure enough, the DDC Q inputs are grounded. Still, it is my understanding complex mixing is done digitally in the FPGA, which should yield perfectly valid quadrature samples, right?
However,
this document implies the TVRX has separate quadrature outputs, I think. For example, on page 61, the mux value (0x----3210) is set in accordance with the TVRX having I and Q outputs. Is this a sensible mux value for two TVRXs?
I guess I am asking what the difference is between quadrature and non-quadrature boards and if that has any impact on your ability to get valid quadrature samples out. Is it that "quadrature boards" do the complex mixing in hardware themselves on the board and send the I and
Q signals to separate ADCs, and the complex mixing isn't done in the FPGA in that case?
Thanks!
Thomas