Try this method
for a 3 bit flash adc use 8 resistors(the 1st and the last resistors should be half of the resistance of the rest resistors)
then connect 7 comparators with the reference input through the resistors
the 7comparators outputs should then be feed to thermometer output(xor gates)
the xor outputs should then be feed to encoder inputs
the encoder outputs are the ultimate result for the 3bit flash adc