Demodulation | EPFL Graph Search

Demodulation is extracting the original information-bearing signal from a carrier wave. A demodulator is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content from the modulated carrier wave. There are many types of modulation so there are many types of demodulators. The signal output from a demodulator may represent sound (an analog audio signal), images (an analog video signal) or binary data (a digital signal). These terms are traditionally used in connection with radio receivers, but many other systems use many kinds of demodulators. For example, in a modem, which is a contraction of the terms modulator/demodulator, a demodulator is used to extract a serial digital data stream from a carrier signal which is used to carry it through a telephone line, coaxial cable, or optical fiber. History Demodulation was first used in radio receivers. In the wireless telegraphy radio systems used during the first 3

A low-power 2.4 GHz CMOS receiver using BAW resonators

Jérémie Chabloz

It has already been a few years since the first appearance of micro-electromechanical systems (MEMS) in academic research. Since then, a broad number of devices have been designed under this generic term. Bulk-acoustic wave (BAW) resonators are among the few of them which have become exploited at industrial level. They are mainly used to implement filters for mainstream telecommunication applications. In a different domain, potential applications for integrated wireless transceivers are flourishing. While some of them require always higher data rates, others need devices with low data rate but even lower power consumption. The goal of this thesis is to explore ways of using BAW resonators to implement building blocks for such a low-power radio and actually verify the postulate that this could help improving power consumption as well as miniaturize key functionalities. For the active integrated circuit part, the choice of a standard digital 0.18µm CMOS process established itself for its low cost and ubiquity. The specifications for the developed radio receiver are calculated for a physical layer derived from the well known Bluetooth communication protocol in the 2.4GHz ISM band with similar applications scenarii but with much lower data rates and wider channel spacing. After presenting the advantages and limitations of the devices, the implications for using BAWresonators to implement a low-power radio are investigated at circuit and system levels and a super-heterodyne architecture is proposed. A selective low-noise amplifier (LNA) is used at the circuit front-end to yield image and blocker rejection. Measurements for the RF front-end comprising an external balun, the selective LNA, a first downconversionmixer and an intermediate-frequency (IF) amplifier showed an overall noise figure of 11dB for a current consumption of 1.5mA under 1.2V. The high selectivity of the design yields an image rejection ratio of at least 50dB and allows to decrease linearity requirements and thus power consumption. A slightly improved version of the same front-end integrated together with the analog baseband signal processing chain but still using external local oscillators showed sensitivities of -96dBm at 100kbps symbol rate and -93dBm at 200kbps with an external state-of-the art FSK demodulator, allowing to extrapolate a global noise figure of 12.2dB for a global current consumption of 2.3mA under 1.2V. The proposed solution for the frequency synthesis uses both a BAW oscillator for the first downconversion to IF and a quadrature quasi-harmonic relaxation oscillator to translate the signals to baseband. The relaxation oscillator is embedded within a phase-locked loop (PLL) for which all the required blocks are discussed. Particularly, a novel modular multi-modulus frequency divider is presented, which does not necessitate complicated logic to yield the wanted division ratio and uses dynamic logic. The necessary digital circuitry to control the frequency generation is discussed as well. Finally, measurements for the complete receiver using the proposed frequency synthesis as well as digital control and demodulator implemented on FPGA are presented.

EPFL2008

CMOS Demodulation Image Sensor for Nanosecond Optical Waveform Analysis

Nicolas Blanc, Lysandre-Edouard Bonjour, Maher Kayal

An image sensor with 256 x 256 pixels and a pitch of 6.3 mu m, suitable for resolving ultrashort optical phenomena, is developed. It is based on a standard CMOS process with pinned photodiode option. The pixel comprises three transfer gates to allow versatile sensor operation whereas repetitive exposure and integration are used to increase the lowest signal level that can be detected. The image sensor is fully functional and demonstrates the ability to demodulate signals in the time-domain with contrast higher than 92% up to 100 MHz. Algorithms for fluorescence lifetime imaging microscopy and three-dimensional time-of-flight imaging are proposed. They allow measurements to be insensitive to background light, subsurface leakage, dark current leakage, and subthreshold leakage of the transfer gates. Lifetimes of free quantum dots are resolved using time-domain demodulation. Range imaging is also shown to be possible with frequency-domain demodulation although background light cannot be suppressed efficiently in the present implementation of the image sensor due to the limited full well capacity.

Institute of Electrical and Electronics Engineers2013

High sensitivity, incoherent differential imaging

Chiara Bonati

Microscopic visualisation of optically transparent samples has been a topic of interest for several decades. Features such as density or chemical composition can influence the optical phase of transmitted light, and phase contrast can reveal these structures. Several methods of phase contrast have been developed, which can be categorised as either interferometric or non-interferometric, based on the type of coherence properties of the light used. In this work, I focus on incoherent based phase contrast, in particular Differential Phase Contrast (DPC). The choice of incoherent light brings benefits such as the absence of distortions like speckle patterns and ringing patterns, increased spatial resolution, and a simpler setup that can be used for in-vivo applications. Moreover, DPC allows reconstruction of quantitative phase maps of the samples. On the other hand, coherent-based techniques demonstrate superior performance in terms of phase sensitivity. The first part of this thesis offers a quantitative analysis of the phase sensitivity of DPC and investigates the influence of optical parameters and sample characteristics. With simulations and experiments, a relation between numerical aperture and phase sensitivity is demonstrated, and the concept of spectral matching is introduced to enhance the contrast. The methods can be generalised to any DPC setup, and allow a-priori investigation of the sensitivity of a DPC microscope at the design stage rather than through testing. Comparison between the best sensitivity that can be achieved in DPC and state-of-the-art interferometric techniques, shows that it is not possible to reach comparable single-shot performances. In this thesis, it is shown that the reason for this limitation is the strong background in DPC images, which degrades the dynamic range. DPC images are obtained with mirrored illuminations, for which the background is identical and the phase term switches in sign. The difference between these pairs of images is computed digitally, which does not improve the limited dynamic range. Lock-in DPC is proposed as a solution: instead of sampling different illumination states, lock-in DPC demodulates the phase signal when the illumination is switched, and the background is never encoded. This is enabled by periodical switching of sources coupled with a smart pixel detector, the so-called "lock-in camera". Part of this work is dedicated to the theoretical description of this method, and the analysis of the expected benefit. Experiments are also described, that demonstrate a factor of 8 improvement in single-shot sensitivity compared to standard DPC. DPC is not the only imaging technique to suffer from high intensity background: it is easy to see how the use of a lock-in camera for differential imaging can be generalised to any situation where weak modulations can be induced over a strong background. Here, an example is presented with lock-in Shifted Excitation Raman Difference Spectroscopy (SERDS). SERDS is an established Raman spectroscopy technique that takes advantage of the Raman emission spectrum being relative to the excitation wavelength to remove unwanted fluorescence emission. Two spectra with shifted excitation wavelengths are measured, their difference is computed, and the fluorescence is thus digitally removed. The parallel with DPC is immediately apparent. Both simulations and experiments are used to demonstrate the advantage of analog demodulation.