A 6GHz Integrated PhaseLocked Loop Using AlGaAs/GaAs Heterojunction Bipolar Transistors

A fully integrated 6-GHz phase-locked-loop (PLL) fabricated using AlGaAs/ GaAs heterojunction bipolar transistors (DDT's) is described. The PLL is intended for use in muttigigabit- per-second clock recovery circuits for fiber-optic communication systems. The PLL circuit consists of a frequency quadrupling ring voltage-controlled oscillator (VCO), a balanced phase detector, and a lag-lead loop filter. The closed-loop bandwidth is approximately 150 MHz. The tracking range was measured to be greater than 750 MHz at zero steady-state phase error. The nonaided acquisition range is approximately 300 MHz. This circuit is the first monolithic HBT PLL and is the fastest yet reported using a digital output VCO. The minimum emitter area was 3 µm x 10 µm with f t = 22 GHz and f max = 30 GHz for a bias current of 2 mA. The speed of the PLL can be doubled by using 1-µm x 10-µm emitters in next-generation circuits. The chip occupies a die area of 2 mm x 3 mm and dissipates 800 mW with a supply voltage of -8 v.