Design And Hardware Realization Of Digital Intermediate Frequency Receiver

Receivers based on analog technique in space TT&C system have many demerits in expansibility, operationality and performance. With the rapid development of digital device and signal processing technology, the analog terminal units in TT&C are replacing by digital ones. In order to solves all the problems in analog system, This paper put forwards a design for multifunctional digital intermediate frequency receiver (DIFR) .The DIFR is built on universal hardware platform based on high-density programmable logic devices referring to software-defined radio (SDR). All DIFR functions can be realized by loading certain program. In this digital processing scheme, the input signal with its frequency 70M are directly bandpass sampled and all the digital signal processing work is performed by FPGA. Complex FFT can accomplish carrier acquisition in a short time without error locking by analyzing in frequency domain. The carrier-tracking algorithm is based on AFC. With the switching between wide and narrow FLL , the carrier-tracking loop can achieves good performance whether frequency changes in high dynamic range or it is in stable state. Side-tone and telecontrol signals are demodulated in digital mode which can achieve good performance in precision and delay.FPGA accomplishes intermediate frequency signal processing work and controls all the peripheral devices. Cascade connecting mode in AGC design can achieve large dynamic AGC range. By using high-performance and high-density devices, the coherent carrier, side-tone and telecontrol signal can be recovered accurately. The DIFR has passed through strict tests and works well. The scheme presented in this paper has certain significance for the fully digitizing of DIFR in TT&C system.