The analogue integrated circuit such as such as amplifier and converter has at least two or two above power source cites a base. To parts of an apparatus of only power source, among them one brings a foot to join normally to the ground. If the mixture signal parts of an apparatus such as ADC and DAC can have voltage of imitate and voltage of digital power source and I/O. Like FPGA such digital IC still can have voltage of many power source, for example kernel voltage, memory voltage and I/O voltage.

 

No matter power source brings crural amount how, IC data manual defined the limit of every power source, include to recommend working limits and the greatest absolute value, and work to keep normal and prevent damage, must abide by these limitation.

 

However, the — inside the working range that the even if of little change — of the power source tension that causes as a result of noise or mains lines wave guide still is recommending also can bring about function of parts of an apparatus to drop. It is for example in amplifier, little power source change can produce input and the little change that output voltage, if pursue,1 is shown.

 

 

Graph 1. The power source of amplifier restrains the sensitivity that indication output voltage changes to power source course.

 

The sensitivity that amplifier changes to power source voltage is restrained with power source normally than (PSRR) will quantify, its define the specific value that changes for change of power source voltage and output voltage.

 

Graph 1 showed typical high-powered amplifier (the PSR of OP1177) follows frequency with about times frequency of 6dB/8 Cheng (times frequency of 20dB/10 Cheng) descendent circumstance. Showed in the graph use losing the graph that two kinds of circumstances leave power supply. Although PSRR is 120dB below dc, but the meeting below more high frequency rate is reduced quickly, there are more and more useless energies on road of power supply cord right now can direct coupling comes output.

 

If amplifier is in drive is laden, and be put in useless impedance on power source course, criterion load current is met course of modulation power source, the noise in adding communication signal thereby and lack fidelity.

 

Although actual PSRR may not give out in data manual, the function of data converter and IC of other mixture signal also can be reduced as the noise on power source. Power source noise also can affect digital circuit with a variety of means, include to reduce allowance of logistic n noise, shake as a result of clock and produce sequential mistake.