I am in the process of designing an SDR and have completed a block diagram of its architecture. Before proceeding with more thorough component identification, I was hoping to receive confirmation that the architecture is "sound." Epic success? Epic fail? Is there anything else that you would add/remove? etc.

Notice that I have at least identified the LT5516 and LTC5599. My plans are also to include a power detector for forward and reverse power detection. Dashed lines represent digital information, most likely via SPI. SPDT RF switches will be controlled via the DSP depending on whether the SDR is receiving or transmitting.

sdr architecture

Any thoughts would be greatly appreciated!


1 Answer 1


The PA doesn't have a BPF directly on its output prior to the TR switch. It's likely it will need one and the one at the antenna should be repositioned to take care of that. Having a bi-rectional BPF for transmit and receive directions is overly complex. If you need a BPF at the input to the RX LNA then put one there as well.

Of significant concern is the software loop to keep the synthesizer perfectly lined-up with the incoming received signal. This isn't a crit but an observation about the synth - it has to be capable of almost analogue resolution. You give no clue about this so I'm making this point!

I also observe that the IQ demod chip is 5V yet the LTC5599 only works from 2.7 to 3.6 volts (I'm planning on using this part BTW) - this means a more complex power supply regime but, maybe you have that stuff covered.

That's me done!

  • \$\begingroup\$ The block diagram is now updated with two individual BPFs - was thinking of using just SAW filters for these. With regard to the synthesizer, one option might be the SKY72300-362 which can increment in 100 Hz steps. Perhaps some external fine-tuning circuitry would be a good idea. The power supply design is the next step once I identify everything on the block diagram as is. Thanks so much for your input, now I am no longer apprehensive about the architecture! May I ask what you are using the LTC5599 for? \$\endgroup\$ May 31, 2015 at 19:30
  • \$\begingroup\$ I'm going to use it to transmit at 800MHz a baseband signal that is about 200MHz wide across a gap between a rotating machine and its stator. Just forcing a magnetic signal so no proper antenna and a very short transmit distance. The 100Hz resolution may not be good enough. I'm no expert on this but I'd be looking at maybe 1Hz resolution because I'm transmitting continuous data (no gaps) and I can't afford to drift out and lose data. \$\endgroup\$
    – Andy aka
    May 31, 2015 at 20:02

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