Query regarding amplifier gain

this datasheet says 25db gain at 100Mhz ... does this gain means power gain or voltage gain??

25dB power gain = 25dB voltage gain. They are the same thing.

Keith

how???
as power gain(db)=10log(pwr)
whereas voltage gain (db)= 20log(Vol)

Correct. So 25dB of power gain means you have 316 times the power. 25db dB of voltage gain tells you that you have 17.78 times the voltage. 17.78 times the voltage will produce a 316 times power gain into a load because the power is proportional to voltage squared.

Keith

Please note that on this sheet you are using a RF device (what I would call a MIMIC - ) and are current bias powered for their operation - see schematic at the end of spec sheet. Also note that this RF device is characterized to work at very specific impedances - 50ohms input and output. Your maximum output is 19.2dBm, or about 90mW into 50ohms, or about 2volts across this load.
From long experience with these style of RF devices they can be temperamental if grounding, PCB layout, grounding, PCB board type, grounding, and input to output isolation and termination is in anyway compromised. And if I didn't say it enough - keep a careful eye on the signal grounding, and supply return paths!
MiniCircuits have some great resources take a look here **broken link removed**

Otherwise good luck.

Strictly speaking dB refers to power gain. It's only equal to voltage gain if the input and output impedances are the same, which is typical for high frequency amplifiers and circuits.

But commonly voltage gain is used simply to indicate gain from input to output of a circuit independent of the relative impedances, such as an audio amp or active filter. In that case the voltage gain and power gain are not usually equal. But power gain is not often used to specify such circuits.