The Tapped Analog Delay

The tapped analog delay (TAD) unit is a newly developed MOS integrated circuit designed specifically for the realization of nonrecursive filters. Such a device greatly simplifies the design of low-frequency filters. One such device has twelve delay taps, each tap separated from its neighbor by two sample periods. The analog input signal is sampled and each sample sequentially stored on one of a group of capacitive storage cells from which it is read out 2k sample periods later, where k is the tap number. Such a design avoids the problems of signal degradation and sampling-rate sensitivity which occur with charge-transfer devices. Outputs are buffered to provide flexibility and freedom from interaction. The basic function performed by a tapped line is that of convolution. As the incoming signal propagates down the line, it is convolved with the tap-weight function. The time-domain output is a measure of the correlation between the input and the function described by the tap weights. Device characteristics are reviewed and performance illustrated in a variety of fiiter designs including Iowpass and bandpass designs. Design procedures are reviewed and a comparison made between theoretical and realized performance.