Band Processor Research Articles

An Efficient Parallel Architecture for Sub Band Processor in Broad Band MVDR Beamformer for Medical Ultrasound Applications

Minimum Variance Distortion less Response (MVDR) algorithm is the key adaptive beamforming algorithm in high resolution Medical Ultrasound Imaging systems. MVDR Beamformer is a frequency domain beamformer, and each frequency sub band need to be processed to generate covariance matrix and the same is computationally costly. Though many VLSI architectures have been proposed for MVDR Beamformer, currently no Complex Correlation matrix generation architecture for frequency sub band has been devised which supports real time implementation of broad band MVDR Beamformer for Medical Ultrasound Imaging. In this paper we show real time MVDR sub array, sub band processor realization for an array with number of elements N=32 and sub array length L=8. To satisfy the narrow band condition of the array we employed 1K point FFT, with 12.5 % overlap. The entire design of MVDR Sub band processor is tested on the Field Programmable Gate Array (FPGA) platform. The implementation results show that the through put of the developed architecture is 600K Complex Correlation matrix generation per second which is equivalent to 65.57 fps to image a 20cm depth target at a Pulse Repetition Frequency (PRF) of 4 KHz, 600 Field of View and 10 lateral resolution and makes the MVDR a viable solution for practical systems.

A DIFFERENTIAL K-BAND UWB TRANSMITTER FOR SHORT RANGE RADAR APPLICATION WITH CONTINUOUS RUNNING LOCAL OSCILLATOR

The design of a difierential K-band UWB (Ultra Wideband) Short Range Radar (SRR) transmitter in 90nm bulk CMOS is presented. Implementation of SRRs in deep submicron CMOS technology is attractive, in terms of cost and monolithic integration of RF font-end with signal base- band processor. The transmitted pulse bandwidth limits the range resolution of the radar system. Due to the wide bandwidth and high frequency of CMOS implementation, UWB transmitters in the K-band are challenging to make and critical for the system performance. The design presented is based on frequency up conversion using a double balanced mixer. The difierential output is combined and matched with the antenna using an on-chip balun. To mitigate local oscillator (LO) leakage of UWB difierential transmitters we propose a new Pulse Generator (PG) design. A switching technique is used to minimize the LO leakage enabling continuous wave operation with very wideband pulses. Measurements of the proposed transmitter achieves a i10dB bandwidth (BW) of 5GHz. Using a Pulse Repetition Frequency (PRF) of 100MHz the peak average power is i40dBm. Compared to measured transmitter performance of a single balanced mixer design, the LO leakage of this dual balanced mixer is decreased with more than 20dB, and is lower than the peak average power of the pulse. It consumes 11mW from a 1.2V supply where 6mW is from the LO.

Effects of noise and spectral resolution on vowel and consonant recognition: acoustic and electric hearing.

Current multichannel cochlear implant devices provide high levels of speech performance in quiet. However, performance deteriorates rapidly with increasing levels of background noise. The goal of this study was to investigate whether the noise susceptibility of cochlear implant users is primarily due to the loss of fine spectral information. Recognition of vowels and consonants was measured as a function of signal-to-noise ratio in four normal-hearing listeners in conditions simulating cochlear implants with both CIS and SPEAK-like strategies. Six conditions were evaluated: 3-, 4-, 8-, and 16-band processors (CIS-like), a 6/20 band processor (SPEAK-like), and unprocessed speech. Recognition scores for vowels and consonants decreased as the S/N level worsened in all conditions, as expected. Phoneme recognition threshold (PRT) was defined as the S/N at which the recognition score fell to 50% of its level in quiet. The unprocessed speech had the best PRT, which worsened as the number of bands decreased. Recognition of vowels and consonants was further measured in three Nucleus-22 cochlear implant users using either their normal SPEAK speech processor or a custom processor with a four-channel CIS strategy. The best cochlear implant user showed similar performance with the CIS strategy in quiet and in noise to that of normal-hearing listeners when listening to correspondingly spectrally degraded speech. These findings suggest that the noise susceptibility of cochlear implant users is at least partly due to the loss of spectral resolution. Efforts to improve the effective number of spectral information channels should improve implant performance in noise.