1)offset voltage : So, If i take a lm339 and kept 1v to the pin 6(inverting terminal)and 1v to pin 7 (non -inverting terminal,i wont get a 0voltage at the output pin 1.I have to maintain the difference 2mVdc.i.e pin 6 = 1v and pin 7 = 1-2mv = 0.998v => then i will get a output of 0v ?
No.
When both inputs have exactly the same voltage, the comparator amplifies its input offset voltage by its voltage gain which is very high.
Its input offset voltage can be negative 5mV, nothing, positive 5mV or anywhere in between. Therefore the output can be open or at 0V.
To make the output go to 0V then the (-) input must be more positive than the (+) input plus the offset voltage.
2)input bias current : 25nAdc for lm339 at VCC = 5v. what is the minimum value of the resistors i should take for both pin 6 and 7 ? if i take R1 & R2=1k ; R3=0.5K ,will that effect ?
From the condition = R3=R1//R2
R1 and R2 = 1k and R3 = 0.5 k. -> will that be cancelling the bias currents ?
No.
The "typical" input bias current is 25nA but you cannot buy a typical one. You get whatever they have which might have the max input bias current of 250nA as shown on the datasheet.
If both resistors are the same value then the input offset current (plus the input offset voltage) will determine what the output will do.
use Ohm's Law to calculate how much input offset voltage will ghe made and its polarity if the input resistors have different values.
3)Common-mode-voltage range = (V(+)+V(-))/2 = (1+0.998)/2 = 0.999V
I do not know what your numbers mean.
The input common-mode voltage range is from 0V to the supply voltage minus 1.5V. That is the range that the inputs work normally.
4) how much is the voltage gain ? since it shows in the data sheet of 10kohms for load ,i will keep 10k at the output. but can i keep 2k ? since it cant take upto 6ma at the output.
The datasheet says the voltage gain is from 50 thousand to 200 thousand when the load is 15k or more. It has limits for the supply voltage and the output voltage swing. It does not say how much the voltage gain is reduced when the load resistance is less than 15k but I think your load of 2k will allow the gain to be fairly high, maybe from 6.7 thousand to 27 thousand.