Charge transfer filter providing recursive transfer functions

Abstract

A filter utilizing charge transfer devices for providing recursive transfer functions is described. The filter includes a circular charge transfer shift register having an even number N of stages, greater than two, a first charge transfer shift register, and a second charge transfer shift register. A first input stage is unidirectionally coupled to the first stage of the first shift register and is also bidirectionally coupled to the N.sup.th stage of the circular shift register. A second input stage is unidirectionally coupled to the first stage of the second shift register and is also bidirectionally coupled to the (N/2).sup.th stage of the circular shift register. A first input sequence of packets of charge representing positive weight components of a signal is applied to the first input stage and a second input sequence of packets of charge representing negative weight components of the signal is applied to the second input stage. All three shift registers are clocked at the same frequency. At the end of each clocking cycle the charge stored in the N.sup.th stage of the circular shift register and in the first input stage are combined and divided into a first part contained in the first input stage, and a second part which is contained in the N.sup.th stage of the circular shift register. The first part of the combined charge is clocked into the first shift register and clocked from stage to stage thereof. The second part of the combined charge is clocked from stage to stage of the circular shift register. Similarly, at the end of each clocking cycle the charge stored in the (N/2).sup.th stage of the circular shift register and in the second input stage are combined and divided into a first part contained in the second input stage, and a second part which is contained in the (N/2).sup.th stage of the circular shift register. The first part of the combined charge is clocked into the second shift register and clocked from stage to stage thereof. The second part of the combined charge is clocked from stage to stage of the circular shift register. Charge division and collection means are provided at the various stages of the first shift register to divide and collect fractions of charge appearing in the various stages thereof. The charge collection means of the various stages are connected together and provide a first output sequence of packets of charge representing the positive components of an output signal. The aforementioned fractions represent the weighting coefficients of the various stages of the first shift register. The second charge transfer shift register is identical to the first shift register. The charge collection means of the various stages of the second shift register are also connected together and provide a second output sequence of packets representing the negative components of the output signal.