A 1.2 GHz frequency synthesizer using a custom-design divide-by-20/21/22/23/24 GaAs circuit

The authors describe the circuit design and the process utilized to fabricate a 1.2 GHz 380-mW divide-by-20/21/22/23/24 GaAs circuit aimed at frequency synthesizer applications. The circuit consists of a 5/6 prescaler, a divide-by-4 circuit, and a four-channel multiplexer. The circuit has been implemented with BFL gates fabricated with 0.7-/spl mu/m planar self-aligned normally-on MESFETs. Further improvement can be expected by utilizing DCFL gates instead. A maximum frequency of 2.5 GHz and an internal active power of 50 mW have been simulated. Consequently the normally-off (N-OFF) GaAs circuit would exhibit a speed by power product four times lower than that of equivalent Si ECL dividers based in bipolar processes being developed today.