High-performance self-aligned gate AlGaAs/GaAs MODFET voltage comparator

A very high-performance voltage comparator circuit has been demonstrated using self-aligned gate AlGaAs/GaAs modulation-doped FET's (MODFET's)and laser-trimmable CrSi-based thin-film resistors. The MODFET master/slave comparator circuits demonstrated analog input resolutions of < 1 and 2.5 mV at sampling rates of 0.5 and 1 GHz, respectively, at Nyquist analog input rates at room temperature. The MODFET comparators operated to sampling rates greater than 2.5 GHz at Nyquist analog input rates. Static hysteresis of less than 1 mV was observed for some comparators at room temperature. The self-aligned gate MODFET's demonstrated average threshold-voltage offsets for closely spaced FET pairs of 2.53 ± 1.15 mV, and typical static hysteresis levels of < 1 to 3 mV. These MODFET comparators demonstrated the highest analog input resolution at gigahertz sampling frequencies ever reported, including comparators fabricated using AlGaAs/GaAs heterojunction bipolar transistors (HBT's).