A CCD frequency prescaler for broadband applications

A broadband, compact, and power-efficient frequency prescaler based on two-phase CCDs (CCD-FP) is described. It is similar in operation to flip-flop-based divide-by-N circuits. However, the maximum operating frequency is determined by the charge transit time between CCD electrodes, rather than the propagation delay of a logic gate in which circuit parasitics limit performance, so that relatively large gate length CCD electrodes (1 μm) can be used in a millimeter-wave device. A prototype CCD-FP has been implemented in a GaAs-AlGaAs modulation-doped CCD (MD-CCD) technology and demonstrated at frequencies up to 18 GHz. The CCD-FP has a constant input voltage sensitivity as a function of input frequency and the output signal is phase locked to the input. Expansion of the prescaler modulus incurs no penalty in speed of operation and very modest increases in power dissipation, circuit complexity, and chip area. In conjunction with PISCES two-dimensional transient simulations of the 1-μm MD-CCD, SPICE analysis predicts that an InGaAs-based CCD-FP is capable of operating frequencies approaching 100 GHz