Circuit generates high-frequency sine/cosine waves from square-wave input

The 74HC74A provides a Q and /Q output at half the frequency of the divide-by-25 output of the 74HC390A. Dividing the 74HC74A output by 2 with the divide-by-2 blocks in the 74HC390A creates two square waves -90° apart. Figure 2 shows a 100-MHz square-wave input, a 12.5-MHz output for the filter clock, and 1-MHz sine and -cosine square-wave output before the dividers. Resistor-divider circuits reduce the amplitude from rail to rail to prevent generation of distortion in the filters.