Dynamic Range of a Digital Radio Receiver with a Photonic Analog-to-Digital Converter

Abstract

The article is devoted to determining the requirements for the preliminary, analog part of the receiver and its structure when using a photonic ADC. The subject of research in this case is the issues of ensuring a large dynamic range of signals at the input of a receiver with a photonic ADC. The parameters and properties of the PADC with optical quantization and discretization are investigated. The distinctive features of the PADC are a high sampling rate, about 100 GHz, the possibility of increasing the carrier-to-noise ratio (CNR) and the effective number of bits (ENOB) due to the amplification of the carrier or modulating signal, and a low noise factor of microwave photonic elements. The presented advantages make it possible to reduce the structure of the analog part of the receiver by eliminating the mixer and anti-aliasing filter, as well as to achieve better sensitivity due to a lower level of internal noise. The study also revealed a limitation of the dynamic range imposed by the photonic element base. The reason for the limitation is the nonlinearity of the electro-optical modulators used and the limitation of the upper limit of the dynamic range to the photodetectors used. All this leads to requirements under which the analog part must provide significant amplification of the received radio signal, as well as the implementation of a variable gain. As a result, structural solutions are presented in the form of multichannel switching circuits. The principle of operation lies in the fact that each channel, consisting of a cascade of linear amplifiers and a PADC, has a different gain, and in the digital processing unit, channels are compared and switched depending on the signal level. At the same time, the level should be in the 'corridor' of acceptable values for the application of the PADC and within the dynamic range. The presented structural solutions will make it possible to implement radio receivers capable of receiving and processing a microwave signal without transferring the signal to an intermediate frequency. At the same time, the required signal amplification level of 105 - 106 can be achieved, which makes it possible to achieve a signal level of 2.5-9.5 V, at which the photonic analog-to-digital converter has the best CNR and ENOB indicators.