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来源:LM317 Electronics Components编辑:Lightech时间:2021-06-15 13:55:56

The last important step is to understand the system's power profile in each operating state (i.e. off, sleep, run, etc), then determine how much time is spent in each state. This is important because it tells you where most of the energy is going and where to spend power supply money and design effort! If your product spends most of its time off, but still biases low power circuitry in the off state, then money spent on high power efficiency might be wasted. Instead concentrate on low-load efficiency and low quiescent operating current to optimize the performance where most battery energy is used. Conversely a product with a real hardware ON/OFF switch, that disconnects the battery, should be designed for peak efficiency at the typical operating load current, not the peak. Of course you still need to consider the maximum loads to ensure that the power supply can supply peak load when needed, but the typical numbers will be best guide to help park the efficiency sweet spot” where it will do the most good.

To achieve FDD, receive signals must be filtered from reflecting signals emanating from the transmitter. This filtering can be done with analog filters in the line interface, or with digital filters after the signal has passed through the analog-to-digital converter (ADC).

Digital duplexing provides the flexibility required to design a widely applicable, future-proof modem with fewer analog components and complex circuit variants. Digital duplexing reduces the need for complex analog interface circuits, and eliminates the need to use different front-end analog filters for every FDD band plan. Digital duplexing does, however, require more performance from the ADC because the echo reflected from the transmitter may be much larger than the receive signal.

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DMT modems are naturally suited to digital duplexing because the central element of these modems–the FFT–handles duplex filtering very well. QAM modems can in theory, perform digital duplexing, but to date have not, because this capability comes at the cost of additional DSP circuitry. Digital duplexing is more easily incorporated into a DMT modem than an SCM modem

Additionally, new frequency plans will likely be oriented to symmetrical operation for private networks, or for country-specific plans. DMT modems can be reprogrammed to meet new band plans; SCM modems currently cannot.

Provisioning a DMT modem to fit a new band plan is easy; the upstream and downstream bands are simply programmed into the modem. SCM requires more filtering to split the bands, and these analog band split filters cannot be programmed to different frequencies. Additionally, these filters require a larger transition band between frequencies than DMT modems, about 1 to 1.5 MHz versus only about 4.3 KHz (Figure 1) . This is another very significant advantage of DMT modems.

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4. Low-Power Operation Contrary to some claims, DMT solutions are both cost and power efficient. DMT VDSL has already achieved power consumption of less than 1.5 W/port with a standards-compliant solution.

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When SCM advocates claim DMT is less power efficient, they usually point first to the FFT. As discussed, the FFT is effectively a programmable filter that separates frequencies. SCM solutions also require filtering (usually in the analog domain), and need additional transmitters/receivers to support multiple frequency bands. Deep sub-micron digital IC technology provides low-power digital circuits for today's FFTs, and future technologies are expected to deliver large reductions in power consumption for multi-channel DMT-based devices.

A detailed analysis of the components of the two types of modems shows that power consumption is very similar for each component. One influential study, by Burton Saltzberg1 , formerly a Bell Labs research manager, compared power consumption for DMT vs. QAM modems, and concluded that a QAM digital datapump actually requires more digital processing complexity than a DMT datapump.

A top executive of the EMS provider said the company is pushing strongly into the medical and instrumentation, automotive, consumer electronics service and storage markets.

The capex spending in telecom still spooks me,” said Chris Lewis, chief financial officer of Jabil at the CIBC Fourth Annual Electronics Food Chain Conference in New York. Telecom is bad, and it's going to be tough for the next few quarters…we can't just sit here and hope it comes back.”

Jabil, based in St. Petersburg Florida, generates approximately 20% of it's revenue from the telecom sector but sees the sector declining 5 to 7% in the fiscal 2002 third quarter ending in May, while the instrumentation and medical operation will grow 13 to 15 percent.

A large part of these new business areas are not outsourced right now and they give Jabil a chance to grow 30% to 35%, ” Lewis said.

ALBUQUERQUE,N.M.—On Sept. 11, 2001, a think tank at Sandia National Laboratories started assessing its advanced technologies against the threat of terrorism. In response to that study, Sandia recently funded a program to counter terrorist threats with microelectromechanical systems (MEMS) — not only to sense dangerous chemical, biological and nuclear agents, but also to identify and track the danger itself — the terrorists.

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