Complex processors like AMD Athlon and Intel Pentium 4, which were made in 180 nm a quarter of century ago, had clock frequencies between 1 GHz and 2 GHz. Pentium 4 used internally a double frequency clock for the simpler 32-bit arithmetic-logic units, i.e. up to around 4 GHz.

Today the manufacturing process could be better optimized than 25 years ago, so some logic circuits much simpler than a 64-bit CPU (the previous were 32-bit CPUs for integers, but they had 64-bit/80-bit FPUs working at full speed), i.e. with much less gate delays per pipeline stage, might be able to reach 12 GHz.

However, something like a 64-bit ALU will certainly not reach 12 GHz. Even a 32-bit ALU is very unlikely to reach 12 GHz. Simple things, like shift registers and Galois-field counters, might reach such speeds, or even higher.

The next CMOS process generation, i.e. 130 nm, already allows making complex processors with more than a half of the maximum clock frequency of the fastest processors of today. It also allows making analog amplifiers and mixers for the 5 GHz WiFi frequency bands.