Gigahertz transresistance amplifiers in fine line NMOS

Two front-end amplifiers for fiber optics applications at gigabit data rates were fabricated in fine-line NMOS. One was designed for operation at 1 Gb/s and a simpler circuit was designed for 1.7 Gb/s, with the function of amplifying a photocurrent into an output voltage. An automatic gain control (AGC) optionally follows the first amplifier. The bandwidth of the first amplifier was measured to be 920 MHz, with optical operation at 800 Mb/s at an optical sensitivity of -28 dB using a pin detector for light at 1.3 μm wavelength. The bandwidth of the second amplifier 32 dB at a bandwidth of 870 MHz. Both circuits operated at less than their designed frequency because of discrepancies between expected and measured transconductances.