[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Xylo-SDR] Architecture review
I'd suggest we take a little time and review the architecture we are
proposing so far.
I think that Phil C summed it up very well as follows:
1. We have a BUS/USB COMMs board to handle communications over the bus
and to/from USB. The main function of this board is to control the
bus and handle communications over the bus. This would be a Cyclone
II - Cypress FX2 based board like what Leon is designing. It could
take on other roles as LE space permits.
2. Since the Cyclone II can do LVDS, maybe we should be looking at
having only LVDS signals on the motherboard bus. This would require
that we either use a LVDS capable FPGA/CPLD or a LVDS
serializer/deserializer chip on each plug in board to talk to this
3. The only clock signals on the bus are for driving the bus
communications. All other clocks needed for the plug-in boards are
generated locally on that board or use SMA/SMB connectors to jump to
other plug-in boards.
4. In certain applications the requirement for a FPGA/CPLD or LVDS
serializer/deserializer could be relaxed and the BUS/USB COMMs board
could be reconfigured (after all it is a FPGA) to give single ended
signals... such as the I2S signals for comms with the audio ADCs and
The research that I have been doing on NCO's (DDS) are for use inside an
FPGA interfaced to the LTC2208. I was not intending adding a D/A to the
output to give us a Tx signal. Phil C suggested using a AD9954 for this and
any analogue front ends we may use. I agree that the level of spurs we get
from the NCO are likely to be similar to the AD9954, the latter will be much
easier to implement.
I also support the idea of multiple FPGA's. One that talks to the outside
world (USB, PTT, key etc) and the backplane - i.e. just what Leon is
designing now. If we need others then lets add them on a board-by-board
basis e.g. the LTC2208 should have its own dedicated FPGA and decimate
down to low frequency signals to pass over the backplane.
Multiple high frequecy clocks and signals over the backplane seems like
asking for trouble.
At the moment we have two boards plus the backplane thought throught.
1. USB etc and backplane interface board with Cyclone II FPGA.
2. Sound card replacement board - Wolfson A/D (or TI etc) for Rx I/Q
signals and TVL320 microphone/line input. Dual D/A converters,
speakers/headset and I/Q to QSE. Looks like this board could also do CW
Tx ( I/Q signals and keyer plus sidetone ) if wanted.
3. LTC 2208 with FPGA for Rx. NCO inside FPGA with D/A converter to
provide Tx local oscillator.
4. Ham band BPF board, use bus switches so can be switched into Rx or Tx
chain. HPF's, LPF's, switchable attenuators and preamp(s).
5. Rf board - QSD/QSE with AD9954 DDS and say 1W output ( only use QSD if
we solve NF problems). PIN diode or bus switches for fast Tx/Rx swithcing.
We need to be able to phase modulate the NCO/DDS on Tx at audio rates so we
can use a high efficiency PA design later on.
The LTC board could form the basis of a nice digital scope or spectrum
How are we doing?
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.375 / Virus Database: 267.14.21/235 - Release Date: 19/01/2006