Current Source Technique Research Articles

High precision measurements of acoustic impedance: Applications to the voice and respiratory tract, musical instruments and their players

The acoustic impedance spectrum of the vocal tract and trachea is important in speech and singing. The operation of musical wind instruments depends on the impedance spectra of their bores, and sometimes also on the impedance spectra of the player’s vocal tract. Here, we describe two measurement techniques. The three microphone technique, calibrated with three non-resonant loads, achieves large dynamic range measurements of the frequencies, magnitudes, and bandwidths of resonant duct maxima and minima. The impedance minima are particularly important in flute family instruments and in the voice, where resonances correspond to minima at the lips. These measurements can also be used to estimate the duct geometry and acoustic properties at the distant end, which may be otherwise inaccessible. The capillary or current source technique has been used to measure impedance maxima inside the mouths of wind players during performance, e.g., where saxophonists tune their tracts to the note played, and for “ecological” measurements during speech and singing that give estimates of resonant frequencies that are rather better than those from formant estimation at high pitch. This technique has recently been updated to run in real-time and made available as open source software, with modest equipment requirements.The acoustic impedance spectrum of the vocal tract and trachea is important in speech and singing. The operation of musical wind instruments depends on the impedance spectra of their bores, and sometimes also on the impedance spectra of the player’s vocal tract. Here, we describe two measurement techniques. The three microphone technique, calibrated with three non-resonant loads, achieves large dynamic range measurements of the frequencies, magnitudes, and bandwidths of resonant duct maxima and minima. The impedance minima are particularly important in flute family instruments and in the voice, where resonances correspond to minima at the lips. These measurements can also be used to estimate the duct geometry and acoustic properties at the distant end, which may be otherwise inaccessible. The capillary or current source technique has been used to measure impedance maxima inside the mouths of wind players during performance, e.g., where saxophonists tune their tracts to the note played, and for “ecological...

A wireless wearable surface functional electrical stimulator

ABSTRACTIn this paper, a wireless wearable functional electrical stimulator controlled by Android phone with real-time-varying stimulation parameters for multichannel surface functional electrical stimulation application has been developed. It can help post-stroke patients using more conveniently. This study focuses on the prototype design, including the specific wristband concept, circuits and stimulation pulse-generation algorithm. A novel stimulator circuit with a driving stage using a complementary current source technique is proposed to achieve a high-voltage compliance, a large output impedance and an accurate linear voltage-to-current conversion. The size of the prototype has been significantly decreased to 17 × 7.5 × 1 cm3. The performance of the prototype has been tested with a loaded resistor and wrist extension/flexion movement of three hemiplegic patients. According to the experiments, the stimulator can generate four-channel charge-balanced biphasic stimulation with a voltage amplitude up to 60 V, and the pulse frequency and width can be adjusted in real time with a range of 100–600 μs and 20–80 Hz, respectively.

High frequency saturated CMOS floating resistor for fully-differential analogue signal processors

A floating resistor on a current source technique is introduced. All the transistors are saturated leading to higher frequency response than previously proposed techniques. Simulated results, using HSPICE level 3, for a 214 kΩ floating resistor have shown a −3 dB frequency of the order of 1 GHz. Its total harmonic distortion at 10.7 MHz and including 2% worst case transistor mismatches is less than –62 dB for fully differential applied signals up to 2 V peak to peak.

Current-Source Converter for AC Motor Drives

The employment of current-source concepts in thyristor converters to obtain adjustable frequency and adjustable current waveforms is presented. The use of a dc filter choke and a current feedback loop to produce a regenerative current source is explained. The simplified inverter commutation circuit made possible by the current-source technique is also discussed. Finally, a brief review of the inherently rugged current-source converter's ability to provide wide range control of an ac induction motor is given.