Abstract: An "automatic power down" method is introduced to design a 4/5 prescaler,with the characteristic of making one of its D-flip-flops power down when it operates in divide-by-4 mode.Implemented with the TSMC 0.25μm mixed-signal CMOS process,the 4/5 MOS current mode logic prescaler is designed with this automatic power down technique.The simulation results show that the new 4/5 prescaler is immune to the "wake-up" issue and thereby retains the same maximum operating frequency as the conventional prescaler.An integer-N divider with this proposed prescaler and with the division ratio 66/67 is manufactured,and it is estimated to save more than 20% of the power compared with the conventional 4/5 prescaler.

Key words: MCML prescaler, automatic power down, frequency synthesizer