dB Off Research Articles

CVR: A Continuously Variable Rate LDPC Decoder Using Parity Check Extension for Minimum Latency

This paper presents a novel IEEE 802.16e (WiMAX) based decoder that performs close to the 5G code but without the expensive hardware re-development cost. The design uses an extension of the existing WiMAX parity check code to reduce the initial decoding latency and power consumption while keeping the decoder throughput at maximum. It achieves similar Frame Error Rate (FER) compared to 5G (0.1 dB off), and most notably the error curves trend down like 5G instead flooring. At FER= 10−3 there is 0.1 dB gain in the FER code performance compared to WiMAX. An implementation of the design is a modified version of the existing fully-parallel WiMAX decoder that supports multi-rate codeword size and reduces the initial latency by 33%. Additionally, for SNR greater than 3 dB, decoding only the shorter code reduces the power consumption by 34%.

Note: A versatile radio-frequency source for cold atom experiments

A radio-frequency (RF) source designed for cold atom experiments is presented. The source uses AD9858, a direct digital synthesizer, to generate the sine wave directly, up to 400 MHz, with sub-Hz resolution. An amplitude control circuit consisting of wideband variable gain amplifier and high speed digital to analog converter is integrated into the source, capable of 70 dB off isolation and 4 ns on-off keying. A field programmable gate array is used to implement a versatile frequency and amplitude co-sweep logic. Owing to modular design, the RF sources have been used on many cold atom experiments to generate various complicated RF sequences, enriching the operation schemes of cold atoms, which cannot be done by standard RF source instruments.

Micromachined reconfigurable microphone array for wind tunnel testing.

A surface micromachined, front‐vented, 64 channel (8×8), capacitively sensed microphone array‐on‐a‐chip devices for aeroacoustic testing is described. The arrays are fabricated using the MEMSCAP PolyMUMPs polysilicon surface micromachining process, with a Parylene‐C passivation layer. The devices are packaged with low profile interconnects, presenting a maximum of 100 μm of surface topology. The array electronics allow the microphone outputs to be redirected to one of two channels, allowing dynamic reconfiguration of the effective transducer shape in software. Measured microphone sensitivity is 0.15 mV/Pa for an individual microphone and 8.7 mV/Pa for the entire array, in close agreement with model predictions. The microphones and electronics operate over the 200–40 000 Hz band. The dynamic range extends from 60 dB SPL in a 1 Hz band to greater than 150 dB SPL. Element variability is ±0.05 mV/Pa in sensitivity with an array yield of 95%. Off‐chip electronics provide 80 dB off isolation. Preliminary wind t...

A 1 GHz CMOS analog front-end for a generalized PRML read channel

A 1 GHz CMOS analog front-end for general partial response maximum likelihood (GPRML) read channel in hard disk drive application has been implemented in 0.35 /spl mu/m CMOS. A continuous time analog filter fulfills the relaxed equalization for GPRML detection and can save up to 35% power consumption for the whole read channel. An analog DFE-based timing recovery loop is implemented to avoid the extremely long latency in the digital signal processing path (Viterbi decoder). The measured performances is 1.1 dB off simulations at 800 MHz and 1.6 dB off at 1GHz. The chip draws 240 mW from a 3.3 V supply at 800MHz clock and 380 mW from a 3.6 V supply at 1 GHz clock.

Active Control of Structurally Radiated Sound from an Enclosed Finite Cylinder

A long, thin aluminum cylinder was configured with two rigid end caps and in strumented with piezoceramic actuators and either microphone or polyvinylidene fluoride (PVDF) structural sensors for narrow-band active structural acoustic control. The input disturbance to the cylinder was generated with a shaker attached by a stinger, and all tests were performed in an anechoic chamber. In the first series of tests, the cylinder was driven with a shaker attached to the end cap, exciting the "accordion mode" of the structure. Upon applying control and using PVDF sen sors, significant levels of global sound attenuation, approximately 25 dB on-resonance and 15 dB off- resonance, were observed in the acoustic field. In both the on-resonance and off-resonance test cases, three control actuators were required to achieve the stated levels of sound attenuation due to interaction between the accordion modes and the cylinder modes. In the second series of tests, the cylinder was driven radially with a shaker to excite higher order cylinder modes. Control was ap plied with six piezoelectric actuators wired to control selected circumferential modes in the first test case, and the actuators were chosen in a helical pattern about the cylinder in the second test case. In the latter case, approximately 10 dB of global sound attenuation was observed in the acoustic field when using microphone error sensors, while results obtained when implementing the PVDF error sensors yielded little sound attenuation in controlling the cylinder modes.

The effect of age and experience on inhibition of the acoustic startle response by gaps in background noise

The acoustic startle response (ASR) is inhibited when the eliciting stimulus is preceded by a brief gap in background noise. The present study examined the ontogeny of ASR gap inhibition in the rat and the role of experience on its development. Independent groups of Long-Evans rats were tested for 3 consecutive days, at one of eight ages ranging from Postnatal Day (PND) 14–16 to PND 98–100. Gaps (0, 2,4, 8,16, 32, or 64 msec) in broad-band background noise (80 dB on/35 dB off) were presented 190 msec prior to the eliciting stimulus (a 13-kHz, 120-dB, 40–msec tone with 2.5-msec rise/decay). The results show that longer gaps (16–64 msec) inhibited the ASR at all ages; however, the magnitude of inhibition increased with age and repeated testing. The efficacy of shorter gaps (4–8 msec) in the inhibition of the ASR improved until PND 35–37, when the adult pattern was achieved. These findings indicate that both the magnitude of ASR gap inhibition and the efficacy of gaps of less than 16 msec are dependent on the age and experience of the animal.