each switched current source utilizing the pulses which contains its corresponding timing information since current sources are used for the purpose of curve fitting the desired output waveform they would each acquire relatively different current output amplitudes resulted from the application of the weighting based on the input signal if the filtered output waveform is to be shape fitted into a sine wave then selective summation of current sources of the filtering buffer apparatus would have to be coded in sine wave magnitudes in other words a set of differently scaled current sources will be needed the different weightings may be established utilizing the method of linear interpolation thus the switch means of each of the switched current sources in the array 250 of fig3 and 4 should be operated in a scheme based on the principle of 34 first on last off 34 so as to obtain a symmetric output waveform various arrangements of these circuits may be utilized to implement the necessary 34 first on last off 34 timing scheme the use of signal latches is one of the most straightforward implementations of the control logic 240 for the management of signal timing each of the switched current sources has a logic control unit associated therewith in other words each switch is correspondingly linked to the latched output of the logic control unit a latch may be considered as a storage element that can maintain its data content for arbitrary periods as is familiar by persons skilled in the art a typical signal latching circuit may have two control inputs say set and reset for example the application of strobing signals at these data latching status inputs.