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Measurements show that delay attributable to the whole transmission, from the digital microphone at the input of the peripheral board, then transmitted, received, demodulated and reconstructed, until it reaches the output of the receiver, is around 530ns. This short delay proves that the system is suitable for ANC applications, in which the latency has to be as small as possible in order to ensure that the noise-cancelling signal is closely synchronised with the ambient noise. Fig. 6: Demodulated (analogue) down-link signal. Digital microphone multiplexing: beyond experimentation The demonstration system described in this article proves that a digital multiplexing system can be realised on a standard 3.5mm audio connector. In the short term, this new technique will make it easier for mobile phone manufacturers to implement ANC. Products now in development by ams will enable one part of the circuit to be integrated together with the microphones and buttons in the headset, and the other part, including the ANC circuitry, in the mobile device. Further into the future, a digital link through the 3.5mm audio connector could also be used for various accessory applications to transmit and receive data at low and medium data rates. The PX8000 brings a new dimension to power analysis with the introduction of high-accuracy time-based measurement. Combining Yokogawa’s leadership in power measurement with its proven expertise in oscilloscope design, the PX8000 offers futureproof technology for the next generation of design engineers. See more at: tmi.yokogawa.com/px8000 or contact +31 88 464 1429 less constant (at least within one data frame), because the downstream information is coded in the current through the mic-wire that at the same time supplies the peripheral board. During one data frame between two 2MHz pulses of the main clock, eight bits are transferred from the peripheral board to the master board (see Figure 5). This supports the ANC application implemented in this demonstration system: the first three bits denote which of the three control buttons in the peripheral circuit have been pressed the next three bits represent the three digital microphones (the main voice microphone, and two noise-sensing microphones) the last two bits are always ‘0’ and ‘1’. This is necessary to automatically adjust the demodulation level in the master board. Furthermore, these two bits are used for lock-out detection, to prove that the data transfer is stable. The data rate of the down-link is 6 x 2Mbits/s = 12Mbits/s. For current modulation, no parasitic capacitors have to be charged and the parasitic inductance is quite low, so highfrequency data pulses can be realised without difficulty. Figure 6 shows a measurement of the analogue output of the current demodulator (in cyan) and the reconstructed digital data pulses (in magenta) on the master board, at a scale of 50ns/division. The yellow signal shows the 2MHz data frame of the down-link. Where power meets precision PX8000 Precision Power Scope Precision Making Time-based precision measurement of power inputs Packed with power-specifi c analysis capabilities Manufactured to the highest standards of quality and reliability Highly fl exible confi guration Familiar and user-friendly interface www.electronics-eetimes.com Electronic Engineering Times Europe February 2014 33


EETE FEB 2014
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