[introduction]In reportChild in equipment, the stability of power source is very important, the power source inhibition to ripple noise ability as much important. Use a description to be oppositePower sourceRippleNoisecontrol capacity, restrain with power source normally than (Power Supply Rejection Ratio) comes token, it is the stability that measures power source to supply and the inhibition to interference the important parameter of ability. It is to often be in electronic amplifier (especiallyOperation amplifier ) orManostatWait for the parameter that norms book appears.

In electronic equipment, the stability of power source is very important, the power source inhibition to ripple noise ability as much important. Control capacity with what will describe noise of pair of power source ripple, restrain with power source normally than (Power Supply Rejection Ratio) comes token, it is the stability that measures power source to supply and the inhibition to interference the important parameter of ability. It is to often be in electronic amplifier (especially operation amplifier) or the parameter that the norms book such as manostat appears.

Power source is restrained than (Power Supply Rejection Ratio) abbreviation PSRR, it inputs ripple and the logarithm that output ripple to be calculated than coming with power source, the unit is decibel (DB) , its computation formula is:

Among them Vripple (In) the ripple that is input end, vripple (Out) the ripple that is output end. Great majority circumstance uses Vripple (In) / Vripple (Out) will calculate, right now PSRR is be worth; If use Vripple (Out) / Vripple (In) will calculate, right now PSRR is negative worth.

Can see from the formula above:

• In design of identical power supply circuit, use PSRR jumps over big parts of an apparatus, output of its power source is jumped over by the influence of power source small;

• In same power source input ripple condition falls, the PSRR of power source circuit of the design is bigger, duan Wenbo of power source output is smaller.

PSRR uses a field

PSRR manages chip in power source (PMIC) medium applying extensive, enclothe the property that includes parts of an apparatus or the circuit such as power source manostat, amplifier to evaluate. It is processor in the system of current model especially (like GPUs, soCs, FPGAs) , high speed is serial interface (be like SerDes, PCIe, USB) , high speed is collateral data (like DDR, LPDDR, GDDR) and the need stabilized power supply that multichannel power source works at the same time is supplied and control power to electrical interference in setting of taller low-pressure power supply, the ripple noise on power source course comes from signal of the wave of switch noise harmony at power source, number to string together a lot of element such as coupling of faze, clock, because the system is right signal is very sensitive, if power source is right the inhibition of ripple noise capacity is insufficient, can bring about signal to shake directly, generation is piled up by accident, affect systematic stability and bring about systematic loss of efficiency.

All all these make the amount of ripple noise abundant that leaves power supply beforehand smaller and smaller, ask the noise of power source ripple of high accuracy controls capacity thereby (PSRR) measure. The test of PSRR applies extensively already in the industry such as equipment of electron of accurate industry, car, medical treatment.

Graph 1. Low voltage applies setting

Accurate industry: In power sourceManostatIt is especially in design of circuit of LDO power source and application, to its the test of PSRR function conduces to the power source stability that supplies for accurate and low-pressure poor power source offerring evaluate reference. Pursue as follows 2 those who reveal is one uses at digital camera, mobile phone to photograph like the head, can apparel the necessary PSRR project that lists on the equipment LDO chip Datasheet that go up index:

Graph 2. Project of LDO chip PSRR (the picture comes from TI)

Car electron: In car electron system, parts of an apparatus of power source of car plan step / it is OK that systematic PSRR is measured help of bigger limit ground evaluates electronic parts / the stability that equipment asks in power supply of car plan step and secure job character.

Graph 3. The car holds power source system

Medical treatment equipment: In medical treatment equipment, the measurement of PSRR can be helped evaluate power source noise to be opposite the influence of precision of medical treatment equipment and stability, reduce the interference that power source noise causes with the oldest rate, ensure of medical treatment equipment mix with the reading with accurate implementation with safety reliably diagnose.

Graph 4. Power supply system of medical treatment equipment

PSRR checks application

PSRR manages chip in power source (PMIC) medium applying extensive, enclothe the property that includes parts of an apparatus or the circuit such as power source manostat, amplifier to evaluate. It is processor in the system of current model especially (like GPUs, soCs, FPGAs) , high speed is serial interface (be like SerDes, PCIe, USB) , high speed is collateral data (like DDR, LPDDR, GDDR) and the need stabilized power supply that multichannel power source works at the same time is supplied and control power to electrical interference in setting of taller low-pressure power supply, the ripple noise on power source course comes from signal of the wave of switch noise harmony at power source, number to string together a lot of element such as coupling of faze, clock, the system is very sensitive to signal, if power source is right the inhibition of ripple noise capacity is insufficient, can bring about signal to shake directly, generation is piled up by accident, affect systematic stability and bring about systematic loss of efficiency.

Those who need attention is in artificial intelligence (AI) the technology develops quickly today, to it relevant circuit / parts of an apparatus presents trend of extremely low voltage power supply, the PSRR that tests chip of its report source control can evaluate power source to be opposite directly of ripple noise control capacity, use at reducing systematic energy loss, improve systematic performance and efficiency, and conduce to prolong the life of chip.

Next graphs are used at artificial intelligence for (AI) memory LPDDR, its job voltage is low already to 0.5V, the amount of ripple noise abundant that leaves power supply beforehand is smaller and smaller.

Graph 5. Use at artificial intelligence (AI) memory LPDDR (picture origin: SAMSUNG)

In view of its the power source demand of low voltage and Gao Tun spit the character of the quantity, if want to ensure its to move in the AI application that calculates force high continuously,setting falls, tall stability and the power supply that controls capacity high to ripple noise is supplied is necessary safeguard, if noise of power source ripple controls capacity insufficient, what can be affected again?

The 1) influence to chip data and algorithm: The ripple noise with little power source may bring about chip data lack fidelity or chip algorithm is wrong, affect the dependability of chip algorithm and accuracy;

2) manages to power comsumption and can the influence that effect optimizes: Chip system needs many computational resource normally, power comsumption management and can effect is optimized become crucial issue. Ripple noise restrains force to differ what affect power source directly to optimize, reduce a system can effect;

3) tackles the impact of stability to radio frequency signal: In the application that correspond in order to come true in signal of processing radio frequency or feels a function, noise of power source ripple affects communication quality directly and the likelihood causes perceptive error.

Graph 6. High-powered chip suffers the effect of noise of power source ripple easily

How should be PSRR measured?

Use oscillograph carries the PSRR curve that with output Duan Wenbo does direct test and scale place needs to input of DUT power source can. Use peaceful overcomes the oscillograph system of noise of Mainstream series low background and high resolution to do accurate test, join is as follows graphic representation:

Graph 7. PSRR checks join sketch map

• Through the AFG infuse of oscillograph specific sweep signal comes linear infuse implement hind introduce DUT;

• Check DUT power source to input end to output Duan Wenbo respectively through oscillograph system;

• The computation that realizes PSRR value through oscillograph PSRR function, data logging reachs curvilinear scale

(origin: Peaceful overcomes science and technology)

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