urian
Full Member level 3
hi,there
i have designed a comparator and the pre-amp is given in pic1.The top mos pair is working in triode region when the CLK signal is low and act as resistors.And the mos pair below the resistors are just switch to perform the dynamic compare.
Recently I found there are some problems in my pre-amp.
In the pic2,I found that the comparator working inproperly.It seems like the bandwidth is not large enough. A input 10mv higher than the Vref will give a wrong negative result.And the input must be 13mv higher than the Vref to give a correct positive.
Then I reduce the W/L of the input mos pairs and increase the W/L of the triode-region mos pairs to reduce the gain of the pre-amp.Now the comparator works likes pic3.This time a input just 4mv higher than the Vref will give a correct positive oresult.
It's so strange that after altering some MOS's W/L, the bandwidth is reduced but the comparator works better than the former.Why does this occur?
The pic4a and pic4b show the individual AC gain and bandwidth of former and latter pre-amp.
i have designed a comparator and the pre-amp is given in pic1.The top mos pair is working in triode region when the CLK signal is low and act as resistors.And the mos pair below the resistors are just switch to perform the dynamic compare.
Recently I found there are some problems in my pre-amp.
In the pic2,I found that the comparator working inproperly.It seems like the bandwidth is not large enough. A input 10mv higher than the Vref will give a wrong negative result.And the input must be 13mv higher than the Vref to give a correct positive.
Then I reduce the W/L of the input mos pairs and increase the W/L of the triode-region mos pairs to reduce the gain of the pre-amp.Now the comparator works likes pic3.This time a input just 4mv higher than the Vref will give a correct positive oresult.
It's so strange that after altering some MOS's W/L, the bandwidth is reduced but the comparator works better than the former.Why does this occur?
The pic4a and pic4b show the individual AC gain and bandwidth of former and latter pre-amp.