Analog‐to‐Digital Conversion for Cognitive Radio: Subsampling, Interleaving, and Compressive Sensing

This chapter explores different analog-to-digital conversion techniques that are suitable to be implemented in cognitive radio receivers. This chapter details the fundamentals, advantages, and drawbacks of three promising techniques: subsampling, interleaving, and compressive sensing. Due to their major maturity, subsampling- and interleaving-based systems are described in further detail, whereas compressive sensing-based systems are described as a complement of the previous techniques for underutilized spectrum applications. The feasibility of these techniques as part of software-defined radio, multistandard, and spectrum sensing receivers is demonstrated by proposing different architectures with reduced complexity at circuit level, depending on the application requirements. Additionally, the chapter proposes different solutions to integrate the advantages of these techniques in a unique analog-to-digital conversion process

A novel switched capacitor frequency tuning technique for continuous-time Gm-C filters

A novel approach for the automatic frequency tuning of Continuous Time Filters is presented. This approach is based on a switched capacitor circuit and only needs three capacitors, some switches and a replica transconductor to adjust the pole frequency of the filter. Despite the simplicity of the scheme, the accuracy of the proposed system is under 1% of frequency error. To evaluate the idea a version of the circuit has been designed in a 0.5 µm CMOS technology with a 3.3 V power supply and simulation results are provided

Fully differential implementation of a delta-sigma modulator based on the pseudo-pseudo differential technique

Flicker noise and distortion are the main limitations in biomedical applications, especially for Switched Capacitor implementations, where the flicker noise is folded into the signal band. To remove the flicker noise and increase the linearity, the Pseudo-Pseudo Differential (P2D) technique has been proposed, where a single-ended signal is processed in a differential way. This paper presents the first silicon implementation of a second order Comparator-Based Switched-Capacitor (CBSC) delta-sigma modulator based on a variation of the P2D technique. Experimental results in a standard 180 nm CMOS technology show an improvement of 10 dB in the Peak SNDR, 5 dB in the DR, and 9 dB in the SFDR over its pseudo differential counterpart, which is the preferred differential implementation for CBSC circuits. Moreover, it is achieved with a reduction in the power consumption

Passive RFID-Based Inventory of Traffic Signs on Roads and Urban Environments

This paper presents a system with location functionalities for the inventory of traffic signs based on passive RFID technology. The proposed system simplifies the current video-based techniques, whose requirements regarding visibility are difficult to meet in some scenarios, such as dense urban areas. In addition, the system can be easily extended to consider any other street facilities, such as dumpsters or traffic lights. Furthermore, the system can perform the inventory process at night and at a vehicle’s usual speed, thus avoiding interfering with the normal traffic flow of the road. Moreover, the proposed system exploits the benefits of the passive RFID technologies over active RFID, which are typically employed on inventory and vehicular routing applications. Since the performance of passive RFID is not obvious for the required distance ranges on these in-motion scenarios, this paper, as its main contribution, addresses the problem in two different ways, on the one hand theoretically, presenting a radio wave propagation model at theoretical and simulation level for these scenarios; and on the other hand experimentally, comparing passive and active RFID alternatives regarding costs, power consumption, distance ranges, collision problems, and ease of reconfiguration. Finally, the performance of the proposed on-board system is experimentally validated, testing its capabilities for inventory purposesMinisterio de Economía y Competitividad TEC2016-80396-C2-2-

A low-pass filter with automatic frequency tuning for a bluetooth receiver

A third-order Gm-C Chebyshev low-pass filter with high linearity and automatic frequency programmability has been designed. The filter is intended to be used as a channel-select filter for a zero-IF Bluetooth receiver. The frequency tuning scheme is simpler and has more relaxed specifications than conventional ones. The filter bandwidth is 0.5 MHz and the overall scheme dissipates 1.1 mA from a 1.8-V supply. The third-order intermodulation (IM3) distortion of the filter for a 1Vpp two-tone signal centered at 350 kHz is -67dB.Ministerio de Ciencia y Tecnología TEC2007-67460-C03-02

Analog CMOS Readout Channel for Time and Amplitude Measurements With Radiation Sensitivity Analysis for Gain-Boosting Amplifiers

The front-end readout channel consists of a charge sensitive amplifier (CSA) and two different unipolar-shaping circuits to generate pulses suitable for time and energy measurement. The signal processing chain of the single channel is built of two different parallel processing paths: a fast path with a peaking time of 30 ns to obtain the time of arrival for each particle impinging the detector; and a slow path with a peaking time of 400 ns dedicated for low noise amplitude measurements, which is formed by a pole-zero cancellation circuit and a 4th order complex shaper based on a bridged-T architecture. The tunability of the system is accomplished by the discharge time constant of the CSA in order to accommodate various event rates. The readout system has been implemented in a 180 nm CMOS technology with the size of 525 μm x 290 μm . The building blocks use compact gain-boosting techniques based on quasi-floating gate (QFG) transistors achieving accurate energy measurement with good resolution. The high impedance nodes of QFG transistors require a detailed study of sensitivity to single-effect transients (SET). After carrying out this study, this paper proposes a method to select the value of the QFG capacitors, minimizing the area occupancy while maintaining robustness to radiation. The nonlinearity of the CSA-slow-shaper has been found to be less than 1% over a 10–70 fC input charge. The power dissipation of the readout channel is 4.1 mW with a supply voltage of 1.8 V.Ministerio de Ciencia, Innovación y Universidades PGC2018-095640-B-I00Consejería de Transformación Económica, Industria, Conocimiento y Universidades P18-FR-3852 y P18-FR-431

A low-pass filter with automatic frequency tuning for a bluetooth receiver

A third-order Gm-C Chebyshev low-pass filter with high linearity and automatic frequency programmability has been designed. The filter is intended to be used as a channel-select filter for a zero-IF Bluetooth receiver. The frequency tuning scheme is simpler and has more relaxed specifications than conventional ones. The filter bandwidth is 0.5 MHz and the overall scheme dissipates 1.1 mA from a 1.8-V supply. The third-order intermodulation (IM3) distortion of the filter for a 1Vpp two-tone signal centered at 350 kHz is −67dB

Design of a band-pass sigma-delta modulator with reduced number of opamps

This paper is intended to compare the performance of a Band-Pass converter structure and its Low-Pass prototype 2nd order Sigma-Delta Analog to Digital converter. For this purpose Matlab simulations for the 4th order Band-Pass converter have been performed and its power consumption calculated when using the equivalent Op-Amp used m the Low-Pass modulator. First of all will be described the method used to calculate the transfer function and, thus the structure of the Band-Pass structure to be tested. After a band-pass transfer function has been obtained it is implemented using reduced number of opamps. This topology is compared to the existing ones and a system level simulation and characterisation is performed. Finally, jitter limitations are studied. Transistor level simulations using Spectre have been done in order to validate MATLAB simulations prior to layout design

Subsampling OFDM-based ultrasonic data communication through metallic channels for monitoring of cargo containers

An enhanced ultrasonic communication system based on piezoelectric transducers for monitoring of goods in cargo containers is presented. The proposed system consists of several sensors placed inside the container, whose data are collected and transmitted outside it. Data transmission is carried out by an ultrasonic communication channel, in order to avoid drilling the wall of the container. The proposed data communication system is based on the transmission of a 128-OFDM signal. This modulation has been chosen due to its robustness to channels with frequency-selective fading and its spectrum efficiency. In order to increase the signal bandwidth and to reduce the power consumption at the internal node (transmitter), the proposed system exploits the non-linearity of the metallic channel to transmit at higher resonance frequencies. Moreover, power consumption at the external node (receiver) is reduced by using a subsampling based receiver, which allows its implementation by low-cost electronics.This work was supported by the Spanish Ministry of Economy and Competitiveness under Projects TEC2016-80396-C2-2-R and TEC2016-80396-C2-1-