there is no s/h signal as it is written in above mentioned page any body tell me wheather i require sample and hold to measure dc voltage

1) some S/H A/Ds sample when the "conversion start" signal is received thus "no s/h signal" does not say "no sampling"
2) sample and hold may be required when the signal changes rapidly and/or the adc is slow. As an example say you have an A/D that samples in 10us then you will read somewhere between the highest and lowest voltage in that 10us timeframe. Often that is better than good enough. The other aspect is that if you sample you will get the voltage at the sample time, sometimes that is totally insignificant. Again as an example with s and h you may measure 3.2V then 3.4V then 3.6V .... without you might have measured 3.3V, 3.5V then 3.7V..... If your s/h is not synchronized to an event s/h is totally irrelevant.

Erik