I used a power supply to supply 1.8V as the Vdd of the tested-circuit, after I connected 1.8V to the Vdd pad of the testing-board, the originally "clean" 1.8V began to shake(the total current is about 70mA,and the shaking is not sinnusoidal).
The phenomenon can be improved by adding 1uF cap between Vdd and gnd Pad,but the shaking still exsited(about 250mVPP). Why the originally clean Vdd is shaked after connected to the testing-board?
By the way,the board only contain an OP amp that I want to test,and some I/O port(ex:header,SMA,switch......),and all inputs are shorted to ground.
the image is the shaking wave after adding the cap between Vdd and ground.
The phenomenon can be improved by adding 1uF cap between Vdd and gnd Pad,but the shaking still exsited(about 250mVPP). Why the originally clean Vdd is shaked after connected to the testing-board?
By the way,the board only contain an OP amp that I want to test,and some I/O port(ex:header,SMA,switch......),and all inputs are shorted to ground.
the image is the shaking wave after adding the cap between Vdd and ground.
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