16-bit coherent receiver (Architecture Proposal)
This is just an idea for further discussion. Please see the performance tests in the previous posts.
Tuner with a differential output (e.g. R820T2 supports maximum 10 MHz bandwith), IF or near Zero IF. The management of the Tuner will be done using I2C (already tested).
The analog signal is processed by the ADC (parallel); if number of the GPIO-pins are not enough, a multiplexer can be used that transfers MSB and LSB for the 16/24-bit ADC. Then, the signal will be read from GPIO, put in memory and sent via network using Ethernet. Fast BBB GPIO can be used (2 PRUs in parallel or using a multiplexer).
Some signal processing could/must be done on the BBB but it is also necessary that the signal can be transferred unchanged via network. Moreover, it is important, that there is no sample lost. 16 bit at 5…10 MSPS is around 90 Mbit/s. May be it is possible to connect an Ethernet or USB3 to PRU GPIOs (the question is still open).
The synchronisation/time stamping of multiple receivers can be done using the Clock/Expansion Card.
The Cyprus FX2LP supports 16-bit GPIF to USB. This chipset is often used at 8bit for some TV sticks but I think it could be expanded to 16-bit,at least the data sheet says it can.
The proposed variant is very interesting and can be realized using the comparable chips from http://www.microchip.com/design-centers/usb/usb-hubs-and-devices/products/usb-transceivers. We have evaluated the chip USB3300, http://www.microchip.com/wwwproducts/en/USB3300; but you need an additional microcontroller (will it be enough?) or FPGA in order to proceed the data from the ADC. The alternative could be also the usage of the Ethernet, e.g. TNETE2201B (http://www.ti.com/lit/ds/symlink/tnete2201b.pdf).
The advantage of the BBB is 2 Real Time PRUs (200 MHz each), so that you can proceed the data with the guaranteed accuracy of 5 ns. Currently, we try to find out, how many bits receivers are necessary. Several days ago, I got an E-Mail from a radio astronomer who asked about 4 channel coherent receiver with 24 bits. The required bandwidth is about 1 MHz.
Which 16-bit ADC are you currently evaluating? LTC2208/2209, ADC9467, or ADS548x?
Nice work!
No, we plan to use the ADCs with much more slower speeds, e.g. LTC2203 (25 Msps)/LTC2202 (10 Msps). The coherent scenarios require narrow band signals, e.g. in the radio astronomy. Therefore, you can even divide this one ADC on the several tuners, e.g. 4. As a result, different scenarios are possible using the BBB: one channel, 2 channels, 4 channels. These different modes can be configured programatically.