Foreword
Design of portable product power source needs systematic level thinking, developing by the equipment of batteries power supply when, the product of low power comsumption such as such as mobile phone, MP3, PDA, PMP, DSC, if design of power source system is unreasonable, the design of the choice of the characteristic combination of the framework that will affect whole system, product, component, software and power allocate. Same, in systematic design, also want to set out to add a consideration more from the angle of economic batteries energy. Contain make can pilot low pressure differs linear manostat (LDO) is right choice.
The power source of radio frequency circuit asks
Circuit of radio frequency of set of chip of base band of most beehive phone needs 3 groups of power supply: In order to satisfy the need of digital circuit, imitate circuit and peripheral interface circuit. The typical cost of the voltage of digital circuit power supply of base band processor comes for 1.8V 2.6V, usually, voltage drop of Li ionic batteries will be shut to the phone when 3.2V-3.3V, LDO has 500 at least to 600mV press difference, not tall to pressing difference to ask. Additional, digital circuit itself is restrained to the output noise of LDO and PSRR(power source than) the demand is not high also, ask to be in only carry gently extremely low static state electricity is had below the condition.
Model of voltage of power supply of circuit of imitate of interior of base band processor is worth is 2.4V to 3.0V, press difference to come in 200mV 600mV. Requirement LDO has taller low frequency (GSM phone controls capacity for 217Hz) ripple, eliminate the batteries voltage ripple that arises by RF power amplifier, need index of inferior static electric current likewise.
The reception of RF circuit and the value of model of power supply voltage that send two shares come for 2.6V 3.0V, among them low noise amplifier (LNA) , first detector, Suo Xianghuan (PLL) , pressure accuse an oscillator (VCO) and intermediate frequency (the LDO that IF) circuit needs low noise, tall PSRR. In applying actually, the function of circuit of VCO, PLL affects index of radio frequency circuit directly, if send the alternative, imitate of the purity of radio frequency chart, receiver,send and receive implement the phasic error of circuit of noise, number. The photograph frequency that noise can change an oscillator is mixed a frequency is characteristic, at the same time oscillator annulus road also can magnify further noise, the possibility arises modulation to carrier wave.
The noise of LDO and power source are restrained than
The low pressure that LDO is a kind of small power comsumption differs linear manostat, it is had extremely low oneself noise and taller power source are restrained than. The block diagram of linear manostat is shown 1 times like the graph.
