AFEDRI SDR is based on AFEDRI8201 integrated circuit, it is Analog Front End (AFE) from Texas Instrument Company (this part obsolete now, but can be found on the market). I know two SDR-s published in the web that are using same chip:
First design from OH2NLT, was one that pointed me to this interesting Integrated Circuits – AFEDRI8201. It has nice design but it was built as stand alone receiver that does all signal processing in its "DSP like" chip dsPIC30F6014A from Microchip Company. This design has very limited usability in my opinion, due to using for RX audio output 12 bit DAC, and 40-MHz signal processing DSP.
Second design, much more robust and can use Personal Computer (PC) for signal processing, but need additional FPGA evaluation board to transfer baseband signal from front end to PC.
My target was - to use AFEDRI8201 as direct sampling receiver and connect it to PC trough USB interface. From PC’s “point of view” the SDR is looking like usual USB Audio Device, that don’t need any additional driver and bring to PC two 16-bit basebandI and Qchannels at up to 250k sample rate, like in multiple existing today Sound Card based SDR (sftrock40, Flex 1000 etc…). And this SDR can be used with existing SDR software like Linrad or/and Winrad (or any of Winrad1.32 branches, like HDSDR), running under Windows and/or Linux OS.
Please see the picture below:
There is short block diagram description:
LPF - Low Pass Filter, in default configuration is using as anti-aliasing filter for from DC to ~28MHz (or any frequency located below Nyquist limit).
Can be easily replaced by band-pass filter (BPF) for desired band in under-sampling acquisition mode when received signal is lying over Nyquist frequency (for example 50MHz, 70MHz band, 144MHz). I tested undersampling mode with this receiver on WFM band (88-108MHz) and on 144MHz band, there is some degradation in sensitivity, so it will be better to add external low noise amplifier (LNA).
VGA - Variable Gain Amplifier, it is built using AD8330 IC from Analog Devices, and adjusted in in this design to give amplification/attenuation of input signal from -6dB up to 44dB.
Direct Sampling Receiver Front End - i.e Analog Front End is built on AFEDRI8201PBF integrated circuit, it is main device of SDR, that providing Input RF signal ADC sampling, mixing and digital filtering, base-band signal data is outputs through specific serial interface, that very similar to I2S but not 100% compatible, for example used in my design CPU, need external help from CPLD, to accept data incoming data. More information about you can find in datasheet. Please pay attention that this device is obsolete on Texas Instruments, but there is many way to achieve this integrated cuicuits from different sources. And I am sure HAM radio society can use it in their applications. For example I have some quantity of AFEDRI8201PBF in my stock.
CPLD - main function of this device to convert AFEDRI8201 base-band (output data) serial protocol to SPI protocol, that can be received by used in design CPU.
CPU - it ARM Cortex-M3 architecture microprocessor - STM32F103R8, from ST Microelectronics, it controls Analog Frond End by additional SPI control channel, receive processed base-band data from Front End and transfer it to PC using USB link and software USB Audio Device and HID device emulation.
Power Supply - Whole receiver is supplied from 5V voltage of USB line, and there is three voltages +1.8V -digital, 3.3- digital and 3.3V analog, that generated from single supply voltage.
Optional UART - SDR contains also RS232 serial interface, in present firmware I am using it for additional debug command shell interfacing, filters coefficients upload and it is possible to upload firmware to CPU trough this interface.
Optional LCD - there is optional parallel LCD interface exists in SDR, LCD is not supported by current firmware yet, cause I am not sure do someone really need it, but can be easily implemented in the future on user request.
The full AFEDRI SDR schematic can be found on my Download page.