A programmable bandpass filter and tone generator using bucket-brigade delay lines

Bucket-brigade devices have been used to build a new type of active filter that is equivalent to a second-order digital filter without the need for complex analog-to-digital conversion. The x It) filter response characteristics, i.e., center frequency and bandwidth, + I depend on the circuit parameters of gain and clock frequency, both e2(t- U of which may be electronically controlled. + By using a variable clock signal, 1023 frequencies can be ac- I e0%, curately selected by the proper setting of ten switches. The selected clock frequency uniquely determines the center frequency of the bucket-brigade filter. The programmable feature of the clock circuit, DELAND therefore, allows the convenient selection of the center frequency u It-T,) of the bandpass filter. A slight modification to the programmable bandpass filter converts it into a programmable oscillator. Thus, any one of 1023 tones can be generated by the proper setting of the switches. A device that ex- D hibits both filter and oscillator functions has been demonstrated in the laboratory.