Software Configurable Receivers

Abstract

Heterodyne and Direct Conversion Homodyne receivers have been studiedfor a long time. It can be shown that the classical advantages as high sensitivity and high selectivity can not be transferred easiliy to the requirements arising from software configurable systems. Already for a dualfrequency receiver the Direct Conversion approach has a clear cost advantage. However, these types ofreceivers require significant effortsfor the correction ofstatic and dynamic errors which in practical cases very often reduce sensitivity and flexibility. Sixport non-mixcing direct conversion architectures may be a multiple alternative to the aformentioned structures: The rectifying process can be very broadband and therefore multi-band capable and the front-end provides a low cost potential. Re-configurable receivers with direct RF sampling can provide multimode, multirate and multiband functions in a single hardware platform. The current bottleneck in the direct digitizing receivers is the analog to digital converter. With currently available analog to digital converters bandpass limited sub-sampling in the carrier frequency range of up to I GHz is possible. The concept of bandpass limited subsampling became recently a very suited architecture approach as the increasing cut-off frequency and speed of semiconductor technologies can be traded against resolution in this concept. Direct digital receiversfor broadcast standards becomefeasible. At still higherfrequencies new analog to digital converter architectures have to be investigated. The specific design of the hardware architecture becomes more and more a compromise between the specifications of the services to be handled by the receiver and the availability of components.Services and standards which rely on a spread spectrum modulation are especially suitedfor direct digital receivers, as the inherent correlation gain, which is achieved in spread spectrum receivers, lowers the requirements with respect to receiver dynamics. The high speed building blocks of a millimeter wave direct digital receiver are composed by low-pass or band-pass filters, the sampling and analogue to digital converter circuits and the decimatorfunctions which convert the high speed sampling rates into lower rates and higher resolution, respectively. The RFfi lters must reduce outof-band spurious harmonics -which can be generated by nearby systems or internal non-linearities -andprovide small in-band transmission losses. Three dimensional micromachined structures can provide high quality factors and low insertion losses at carrier frequencies of 24 GHz. Transimpedance amplifiers for a bandpass limited subsampling approach and limiting amplifiers can be designed and realized in commercial SiGe technology. A sampling head itsself is composed ofa Schottky diode quadruple.

New-Wave Radio

“…On the other hand, for QAM/MPSK data, more research is needed to develop advanced algorithms, new interferometer designs, and related software implementations in DSP [9]. SPI radio platforms are now being developed in software defined radios (SDRs) for 2010 car models, proposed to be fabricated in Germany [10], [11]. Recently, CMOS transceiver chips [12] with SPI modulators and demodulators were fabricated at 60 GHz for commercial applications.…”

Experimental Performance Comparison of Six-Port and Conventional Zero-if/Low-if Receivers for Software Defined Radio

“…Since some theoretical [3][4][5] or simulation-based [6] studies have been published, this paper presents an experimental comparison based on measurement results. Two SDR receiver prototypes have been developed for this purpose: a broadband six-port receiver, described in Section 2, and a dual zero-IF/low-IF receiver, presented in Section 3.…”