In this paper we present a merged Digitally Controlled Oscillator DCO and Time To Digital Converter TDC architecture. The DCO is a nine-stage interpolative ring made by NOR cells. It is designed for TV applications and it is implemented in 65nm CMOS process. The oscillator has a large frequency range, from 50MHz to 500MHz, and a 28 × 39μm 2 core area. It consumes 1mA from 1.2V power supply, and it has −120dBc/Hz@5MHz phase noise for 420 MHz carrier frequency. The oscillator states are directly used to measure the delay between input and output clocks. The resulting TDC is compact, very economic in power consumption and it has a resolution that is equal to 1/18 of the oscillation period. The DCO and the TDC are used in an All Digital Phase Locked Loop ADPLL.

Spectrum sensing for cognitive radio requires speed and good detection performance at very low SNR ratios. There is no single-stage spectrum sensing technique that is perfect enough to be implemented in practical cognitive radio. In this paper, the authors propose a new parallel fully blind multistage detector. They assume the appropriate stage based on the estimated SNR values that are achieved from the SNR estimator. Energy detection is used in first stage for its simplicity and sensing accuracy at high SNR. For low SNRs, they adopt the maximum eigenvalues detector with different smoothing factor in higher stages. The sensing accuracy for the maximum eigenvalue detector technique improves with higher value of the smoothing factor. However, the computational complexity will increase significantly. They analyze the performance of two cases of the proposed detector: two-stage and three-stage schemes. The simulation results show that the proposed detector improves spectrum sensing in terms of accuracy and speed.

Cognitive radio is a solution to the problem of radio spectrum scarcity. It gives the opportunity to a secondary user to exploit the spectrum allocated toa primary user. The main function of cognitive radio is spectrum sensing whichhas gained new aspects in the last decades to determine opportunistic spectrum holes. There are many spectrumsensing methods proposed in the literature. The Performance of thesetechniques may vary in different situations; it can be described by probability of detection, probability of false alarm, and sensing time. It is therefore important to compare and indicate the best scheme for a specified scenario. In this paper, we propose a classification of the main approaches of single user spectrum sensing based on its synchronization requirement into two main categories: coherent detection and non-coherent detection. The coherent detection needs some or full prior information about the primary user signal for detecting it, where the non-coherent detection does not need any prior information about the primary user signal for detecting it. In addition, we highlight the advantages and disadvantages of narrowband and wideband spectrum sensing procedures along with the challenges involved in their implementation.Furthermore, we introduce the concept and basics of cooperative sensing and interference based sensing.This paper helps the designer to be familiar with all the techniques used to achieve spectrum sensing.