A circuit having versatility synthesizes one-bit digital signals to generate a ternary signal. Each the data unit occupies one time slot of the frame and the data units are encoded to differentiate between payload data and control codes. The system includes a second expansion valve and a refrigerant heat exchanger connected in parallel with the first expansion valve and the refrigerant evaporator. Halftone cells can be formed in a variety of patterns but generally their threshold values grow from a minimum value to a maximum value.