Digital convergence, in recent history, has been prevalentin the consumer equipment domain and the designengineers in this Area have been struggling with a plethoraof emerging standards and protocols. What lessons can welearn from their struggle? The same dilemmas now existin in-vehicle telematics and infotainment systems but withthe added issues of extremes of temperature, safety,security, and time in market.
Photodiodes can be broken into two categories: largeArea photodiodes with their attendant high capacitance(30pF to 3000pF) and smaller Area photodiodes withrelatively low capacitance (10pF or less). For optimalsignal-to-noise performance, a transimpedance amplifi erconsisting of an inverting op amp and a feedback resistoris most commonly used to convert the photodiode currentinto voltage. In low noise amplifi er design, large Areaphotodiode amplifi ers require more attention to reducingop amp input voltage noise, while small Area photodiodeamplifi ers require more attention to reducing op amp inputcurrent noise and parasitic capacitances.
Low power operation of electronic apparatus has becomeincreasingly desirable. Medical, remote data acquisition,power monitoring and other applications are good candidatesfor battery driven, low power operation. Micropoweranalog circuits for transducer-based signal conditioningpresent a special class of problems. Although micropowerICs are available, the interconnection of these devices toform a functioning micropower circuit requires care. (SeeBox Sections, “Some Guidelines for Micropower Designand an Example” and “Parasitic Effects of Test Equipmenton Micropower Circuits.”) In particular, trade-offs betweensignal levels and power dissipation become painful whenperformance in the 10-bit to 12-bit Area is desirable.
The equal-Area theorem●This is sinusoidal PWM (SPWM)●The equal-Area theorem can be appliedto realize any shape of waveforms
●Natural sampling●Calculation based on equal-Area criterion●Selected harmonic elimination●Regular sampling●Hysteresis-band control●Triangular wave comparison withfeedback control
The makers of handheld medical, industrial and consumerdevices use a wide variety of high resolution, small tomedium sized color TFT LCD displays. The power supplydesigners for these displays must contend with shrinkingboard Area, tight schedules, and variations in displaytypes and feature requirements. The LTC®3524 simplifi esthe designer’s job by combining a versatile, easily programmed,TFT LCD bias supply and white LED backlightdriver in a low profi le 4mm × 4mm QFN package.
In a recent discussion with a system designer, the requirementfor his power supply was to regulate 1.5Vand deliver up to 40A of current to a load that consistedof four FPGAs. This is up to 60W of power that must bedelivered in a small Area with the lowest height profi lepossible to allow a steady fl ow of air for cooling. Thepower supply had to be surface mountable and operateat high enough effi ciency to minimize heat dissipation.He also demanded the simplest possible solution so histime could be dedicated to the more complex tasks. Asidefrom precise electrical performance, this solution had toremovethe heat generated during DC to DC conversionquickly so that the circuit and the ICs in the vicinity do notoverheat. Such a solution requires an innovative designto meet these criteria:
Size, output flexibility and efficiency advantages havemade switching regulators common in electronic apparatus.The continued emphasis on these attributes hasresulted in circuitry with 95% efficiency that requiresminimal board Area. Although these advantages are welcome,they necessitate compromising other parameters
Notebook and palmtop systems need a multiplicity ofregulated voltages developed from a single battery. Smallsize, light weight, and high efficiency are mandatory forcompetitive solutions in this Area. Small increases inefficiency extend battery life, making the final productmuch more usable with no increase in weight. Additionally,high efficiency minimizes the heat sinks needed onthe power regulating components, further reducing systemweight and size.
The design of battery-powered equipment can often bequite challenging. Since few ICs can operate directly fromthe end-of-life voltage from a 2-cell battery (about 1.8V),most systems require a DC/DCconverter. The systemdesigner often has a limited Area in which to place the DC/DC converter; associated inductors and capacitors must be
