calculation of Power consumption

[dinosaur078]

dear every body
i need to calculate power consumption of 1 circuit. my friend told me , i should connect my output of circuit with 1 capacitor with it's value is 5pF . then i will measure the current value and apply equation: P= u.i
could y pls explain to me , why i need connect my output of circuit with a capacitor with it's value is 5 pF

 

[varunkant2k]

What is the circuit ? it all depends on the loading you are using your targeted circuit.
Better post the schematic and application.

 

[dinosaur078]

dear vảunkant2k
it is just 1 VCO with only 1 output

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this is my circuit

 

[varunkant2k]

For any circuit, if you are going to characterize , you need to measure 2 parameters.
1. Quiescent current, 2. Full load current.
1=> Need no loading, and measure the total dc current and multiply it with the supply voltage. This will give you the Quiescent power consumption.
2=> Full load, (with load) you need to load targeted loading at the output node and then measure the supply current and multiply this with supply. It should give you total power consumption.

VCO generally loads to phase correction block and buffer.This all together may give capacitive loading in the range from 5p-10pF.So make assessment and add maximum output cap you expect.
Hope this will help you.