A Fast Bipolar-IGFET Buffer-Driver

Due to the high output impedance normally associated with Insulated-Gate Field-Effect Transistors (IGFET) two problems often arise in digital I G F E T integrated circuits: (i) Charging and discharging times for capacitances external to the integrated circuit are long compared to the corresponding times for internal circuit nodes. («) Interfacing with bipolar logic requires I G F E T s to provide and/or sink currents which are larger than those normally available from I G F E T s with typical integrated circuit geometries. Attempts to solve these problems usually involve large I G F E T inverters or push-pull drivers as output stages. Since these types of output interface circuits employ large-geometry IGFETs and have higher input capacitances than those capacitances typically found at the nodes of the internal I G F E T circuitry, the overall result is that circuit speed is degraded at the output interface. This paper discusses the use of a self-isolating bipolar-IGFET (BIGFET) integrated structure in an output buffer-driver. Although this structure has been previously proposed, 1 - ' there have been no reported experimental studies of improved circuit performance when the B I G F E T is incorporated directly on a monolithic p-channel I G F E T 363