Parameter-setting approach to obtain high performance CTD transversal filters from devices with significant CTI and FPN

An adjustment apparatus for adjusting tap weights in order to achieve a desired frequency response for a charge-transfer-device (CTD) transversal filter having a CTD filter input, a tapped-CTD delay line having a CTD-delay-line input responsive to said filter input and a CTD delay-line output at the opposite end of said delay line from said input, wherein said CTD-delay line has a pluraIity of charge-storage cells having CTD-tap outputs responsive to said cells, said CTD-transversal filter further having a plurality of adjustable tap-coefficient-weighting stages having inputs responsive to said CTD-tap outputs and having weighted outputs, said CTD-transversal filter further having an adder stage for adding together said weighted outputs to produce an adder output signal, said CTD-transversal filter having a CTD-filter output responsive to said adder-output signal, and wherein said adjustment apparatus comprises:

• means for determining the charge-transfer inefficiency for each of said charge-storage cells;
• means for providing an adjustment test signal to said CTD-filter input;
• a reference transversal filter having a reference filter input responsive to said CTD-delay-line output, a tapped reference delay line having a reference-delay-line input responsive to said reference filter input, wherein said reference-delay-line has a plurality of delay stages arranged in sequence along said delay line and having reference tap outputs responsive to said delay stages, said reference transversal filter further having a plurality of reference tap-coefficient-weighting stages set in accordance with said desired frequency response, said reference weighting stages having inputs responsive to said reference-tap outputs and having weighted reference outputs, said reference transversal filter further having a reference adder stage for adding together said weighted reference outputs to produce a reference adder output signal, said reference transversal filter having a reference-filter output responsive to said reference-adder-output signal;
• means for comparing and producing an indication of the difference between said reference-filter output and said CTD-filter output;
• a plurality of means for subtracting the products of each reference tap output and its corresponding CTD-cell charge-transfer inefficiency from the preceding reference-tap output, wherein said cell charge-transfer inefficiency is responsive to said means for determining;
• and
• a plurality of means for adjusting said CTD tap-coefficient-weighting stages responsive to said indication produced by said means for comparing and producing and to each corresponding means for subtracting.

For a charge-transfer-device (CTD) transversal filter including input terminal means for receiving test signals representative of a pseudo-random-noise sequence, output terminal means for providing a filtered output signal having a particular frequency response, a tapped delay line interconnected with said input terminal means and having a plurality of series connected, charge-storage cells having tapped outputs responsive to said cells, and a plurality of tap-weighting gain stages respectively connected to said charge-storage cells to set the tap-weight coefficients of said cells,

• the improvement of a tap-weight-coefficient adjustment circuit to selectively adjust the tap-weight coefficients of each of said gain stages for generating the filtered output signal having the particular frequency response, said adjustment circuit connected in feedback relationship between the last charge-storage cell of said tapped delay line and said gain stages and comprising a reference transversal filter for receiving an unfiltered signal from said tapped delay line and providing a reference output signal in response to the test signals at said CTD transversal filter input terminal means, and
• means for setting the tap-weight coefficients of said gain stages in response to the difference between the reference output signal provided by said reference transversal filter and said filtered output signal provided by said CTD transversal filter, the characteristic charge-transfer inefficiencies of the charge-storage cells of said tapped delay line, and the response of said charge-storage cells to the test signals applied to said CTD transversal filter input terminal means.