How to get the specification of blocks in 8bit SAR ADC

design problem....

hello everyone,
i am a beginner at analog circuit design,after reading some basic books and materials, i want to design a 8bit SAR ADC, but i do not know how to decide some block's SPEC in it. what i mean is that when you get a whole SPEC about xxx..bit ADC, how you get the spec about the component of the ADC...
for example,
3.3-V, 8-bit, 375k/s clock CMOS Successive-approximation Analog-to-Digital Converter. use 0.13um 1.2v/3.3v logic model CMOS Process. It is 180K bandwidth. i use a S/H circuit to get the input signal,following a buffer(opamp in unity-gain structure), then translate the signal to one input of comp, the other input signal of comp comes from the 8bit DAC(R-2R), then send the result to SAR logic...so how to get the spec about opamp,comp S/H,DAC...
thanks in advance.
baggio

I am also confused about it? Can any body help u sregarding this??

3.3V mean your block supply all corner cover and 10% variation.
8-bit decide the DAC DNL and INL, and comparator resolution.
all error sum less than 1/2 LSB.
375k/s: in SAR you must know your convert clock frequency.
your convert clock =375*(8+N)
where N is clock cycle for sample and data output etc.
Convert clcok and bit number decide your DAC detting time and S/H bandwith & gain.