illustrated as directing one of current generators 308 a b to each of the differential output line 304 dac 300 is in fig3 shown as providing a zero overall output a count of 1 is provided by changing a position of 1 of switches 310 a b to reduce the current in one of the differential output lines by u00bdi0 and to increase the current flowing in the differential output line by u00bdi0 giving a total change in the differential output of 1i0 most of the discussion so far has been focused on 4 bit dacs while this is convenient for explanatory purposes it is an impractically low resolution in many applications the technique can readily be extended to 5 or more bits but the larger current sources sinks if implemented using larger transistors require larger silicon area for moderate to high resolutions say 7 bits or more the matching requirements for the dac start to become expensive in silicon area the impact of mismatch on a dac can be reduced by thermometer encoding in this type of dac coding the currents are all equal rather than binary weighted as shown below for a three bit thermometer code unsigned compared to binary weighting this technique uses a larger number of smaller current sources this eases the matching requirement and reduces the silicon area of the current sources this is because the matching accuracy is governed by the ratio of the largest and the smallest current generator and with thermometer coding the biggest current generator is smaller than.